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University of Puerto Rico

Mayagez Campus

10

Forensic Surveying:

Essential in a Precise ReconstructionWritten by:

Randolph Ortega Gonzlez

Ingrid N. Agosto Rubio

Ronnie Ruiz Ruiz

Norma I. Torres Torres

Rubn C. Soto Maysonet

Josu A. Muiz Figueroa


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Abstract

Forensic Surveying makes use of applications of surveying principles, methodologies and

techniques, for purposes of the law. Currently, most of forensic surveying investigations are

carried out in a civil litigation context rather than a criminal one. Surveyors perform accurate

scene reconstruction, allowing experts on accident cases to have all the necessary information to

analyze the accident scene. Although the field of vehicular accident reconstruction is one of the

most noticeable forensic engineering specialties, it doesnt indicate that cant be applied to other

types of accidents like: electrical, industrial, chemical, structural collapses and a wide variety of

criminal cases.

There are many situations in where the work of a surveyor is an important asset for the

reconstruction of a scene. Traffic accidents are no exception, thats why we focus this research

paper to that matter, given that is the most common type of accidents nationwide, making them

useful to study and complete an accident reconstruction scene. The collection of evidence in

forensics is important because it guides the pace of the investigation, as it will determine how

accurate the recreation will be.

In order to obtain all the essential information we need to apply methods of land

surveying altogether with forensic science. An important tool has help experts go beyond

expected as new technological innovations of this era have allow the surveyor to gather results in

short time, making the investigation more accurate. And by using computer software, creating an

animated scene of the desired study analysis we can add a realistic focus of what really happen in

a three dimensional way.


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Introduction

Land surveying defines land boundaries and determines precise geodetic location of

points. Land Data collected by a land surveyor who serves as a forensic expert analyzes and

recreates accident scenes and mostly is included as evidence at a litigation, hearing or lawsuit.

To accomplish all these, surveyors use some basic principles that allow them to show that a

proper investigation has been performed accurately.

The aim of these investigations is to determine what, how and where actually happened

during the event, based on the physical evidence. Some evidence might include witness

statements or descriptions from people who were actually part of the event. Forensic Surveyors

and Engineers have to convey technical information to provide complete and accurate

information to people who were not knowledgeable in surveying, engineering or forensic

sciences. The responsibility of a forensic surveyor and an engineer is to lookout for the safety,

the environment, and wealth being of the community by providing a quality service without

getting involve with any of the two sides. Ultimately the Justice Department is responsible of

enforcing the law, although the forensic surveyor and engineer provide the facts throughout a

compilation of data based on the principle of field techniques.

This paper discusses the duties and responsibilities of a surveyor as a forensic expert with

specific reference to construction sites and traffic scenes. Also describes the recommended

procedures to collect information in forensic surveying, as well as the common instrumentation

used, and discusses the safety considerations requires to properly collect information in a

adequate way.


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Surveyors Duty and Responsibility

The American Congress on Surveying and Mapping (ACSM) defines surveying as the

science and art of making all essential measurements to determine the relative position of points

and/or physical and cultural details above, on, or beneath the surface of the earth, and to depict

the, in a usable form, or to establish the position of points and or details. This way surveying

determines the relative spatial location of points on or near the surface of the Earth. Several

surveying techniques exist to define the location of those points as well as boundaries lines.

Through history the definition of boundaries has been very important. Theyve been mentioned

in the Bible, Numbers 34:6 says As for the western border, ye shall even have the great sea for a

border; this shall be your west border, proving that the work of surveyors have existed through

centuries.

All sciences have been specialized over time, and surveying has expanded to developed

different branches of surveying. For instance: hydrographic surveying, geodetic surveying,

topographic surveying, construction surveying, cartographic, plane surveying, digital

photogrammetry, remote sensing, LIDAR and forensic surveying. Hydrographic surveying;

which works with bodies of water and coast lines, it is recorded on charts, and records such

features as bottom contours, channels, buoys, and shoals. Geodetic surveying is applied to large

areas of land, which takes care of the Earth surface curvature. Plane surveying, which is applied

in areas sufficiently small where the Earth's curvature is negligible and can be discarded.

Plane surveying dates from ancient times and was highly developed in Egypt, although

some event have required its uses in marking boundaries for settlements; as both George

Washington and Thomas Jefferson presidents of United States worked implemented as

surveyors. Topographic surveying, employ to determine relief, route surveying, mine surveying,


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construction surveying; or according to the method used, e.g., transit surveying, plane-table

surveying, and photogrammetric surveying (Anderson and Mikhail, 1989). And forensic

surveying that has evolved to be one of the most important branches because in all investigation

scenes surveyors need to find all evidence that could explain the case.

A forensic surveyor maps scene of automobile wrecks, industrial accidents, car collisions,

boundaries disputes and others. Among his responsibilities are to recreate, to map and analyze

accidents and crime scenes by compiling data in the field. But also a forensic surveyor serves as

an expert witness in court cases and provides testimony to reconstruct scenes during litigation.

To recreate the scenes, surveying equipment such as Global Positioning System (GPS), digital

photogrammetric cameras, laser scanners, spatial station and reflectors are used to determine

precise angles, distances and location. The processed measurements allow having a proper

reconstruction of the forensic scenes in court. Surveyors use technical skills to establish the

cause of loss or damage, review the degree of damage and provide a complete description of

scene in a report.

As many responsibilities the forensic surveyor have, they also have to perform

retracements, which in essence is the action of relocating original evidence in the original survey.

In surveying a tract of land according to a former plat or survey, the surveyors duty is to

relocate, upon the best evidence obtainable, the courses and lines at the same place where

originally located by the first surveyor on the ground. The original survey in all cases must,

whenever possible, be retraced, since it cannot be disregarded or needlessly altered after property

rights have been acquired in reliance upon it(Wilson, 2008). The main objective of the surveys

is to follow, as closely as possible, the footsteps of the original surveyor and reestablish property

corners in the same position in which they were originally placed.


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Accident Scenes

There are a variety of accident scenes where the work of a surveyor is an important asset

for the reconstruction of the scene. No matter the nature of the accident, the collection of

information provided by a surveyor is very important because it represents the fundamentals for

calculations that need to be analyzed for the scene and used for safety criteria. Basically, the

reconstruction of any accident begins with a survey of the scene, meaning that the reconstruction

of an accident has just started.

The reconstruction of an accident considers the aspects of physics, dynamics,

conservation of energy, mechanical analysis, and engineering principles, depending on the type

and/or place of the accident. The most difficult of them is to determine how an occupant moves

with respect to the crashing vehicle (the occupant kinematics). The injury that may have

sustained by the occupant determines quite often the occupants kinematics. To determine it, an

enormous amount of physical information is required in addition to the complexities of solving a

very difficult problem in dynamics. This information includes knowing the properties of the

vehicle interior structures that may be contacted by the occupants. The actual contact points in

the interior of the vehicle and the occupants body, since this will then change the direction of

motion of the occupant, the dynamic response of the human body to impact, and the details of

how the vehicle is moving as a function of time.

The scenes where the surveyors work is used could vary from personal injuries cases to

severely traffic accident. But, in almost every case, an accident reconstruction engineer needs a

survey of the scene to reconstruct it. Accident scenes mainly refer to construction sites and to

traffic accidents.


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Construction Sites

The surveyors work is essential in a construction project, because in every construction

project they establish what goes and where according to the plans approved by the authorities. In

other words, the construction project is completely dependent of a surveyors work. The

surveyors work establishes the location and alignment of highways, bridges, buildings, pipes,

and all other man-made objects requiring a great deal of precision. The Surveyor is the first one

to arrive to a construction site and the last one to leave. They are in charge of making sure that

the structure is in line with the original plans.

When at construction sites, they should make a as-built of the structure and make sure

this structure is as it was planned. However these two are almost never the same. In a

construction site, there are change orders from day to day, which alters the original plans. That is

the reason that at the end of a project, the surveyor performs an as built of the project. All the

modifications along the construction site are recovered and registered. For that reason, the as

built should be made with a high grade of responsibility, because eventually the work made by

the surveyor will become the official plan of the construction development.

Even though the construction is concluded, accidents are still bound to happen. In some

cases, these projects will have secondary effects on its environment and can cause damages to

the environment around it. The effects might include: landslides, flooding and soil failures,

among others. The use of a topographic map of the area affected, before and after the accident,

defines the determination of the responsibility in the accident. The information provided by the

surveyor quantifies the magnitude of the damages.


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Traffic Accidents

Traffic accidents are the most common type of accidents nationwide, which makes them

the most reconstructed accident scenes. There were approximately 6,420,000 car accidents in the

United States in 2005. Almost 2.9 million people were injured and 42,636 people were killed

(Car-Accidents.com). The financial cost of these crashes ascended to nearly $230 billion. In

Puerto Rico, the cost of damages due to transit accidents raises up to $750 million (Alameda and

Lara, 2008). Traffic accidents are a big part of the economy in the United States since millions of

dollars are spent in damages and legal expenses every year.

The field of traffic accident reconstruction attempts to provide insight into the essential

character of such mishaps. This field has been recognized by the legal system for a long time,

since 1920, in a Wisconsin case, which involved a truck that struck a pedestrian who was trying

to board a streetcar, the court admitted into evidence an opinion based on skid marks (Hicks,

2001). The reconstructions of these accidents are essential to determine the responsible parts of

these accidents, and who should be responsible for these costs.

These investigations and reconstructions are based on mathematical and physical analysis

performed by forensic surveyors and engineers trained in their respective fields. The principles

based on Newtons Laws of Physics (Equation 1), The Conservation of Momentum (Equation 2),

The Conservation of Energy and Work Principles

(Equation 3). Throughout the use of this principles the

cause of the accident is analyzed to determine, whether

if it due to high speeds or to a defective design or

construction of the road, or to any other factor.

F=M*A (Equation 1)

(Equation 2)

(Equation 3)


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Commonly the accident reconstruction implies to work

backward; from the final position of the vehicle(s), to the

initial of the event. Calculations, either by hand or by

computer, are performed using the available data in

conjunction with the physical and dynamics principles

mentioned before. These calculations done by the

reconstruction surveyor are based on distances and parameters

obtained in the scene. In car accident problems at the moment

of the impact, the impulse-momentum principle is particularly

useful since the resultant external force acting on the system of colliding bodies is zero. This

then leads to the principle of conservation of linear momentum, which states that the linear

momentum of a system of colliding bodies is conserved at impact. This principle, combined

with the information left at the accident scene and the vehicle data, is often sufficient to solve for

the velocities of the vehicles at impact. With these velocities we can determine if there is

negligence or irresponsibility by any of the drivers.

Collection of Evidence

The collection of evidence in a forensic scene is important because it sets the pace for the

investigation, as it will determine how accurate the recreation will be. Stains, liquids and

substances of any nature (blood, oil, medications, etc.) hair, fibers, glass, paint, firearms, tool

marks, documents, fingerprints, tire marks, missing components, and road signs are considered

intrinsic evidence of traffic accidents. The use of photographic evidence provides additional

information to study the accident as well to have instant recording of the circumstances.

Evidence such as the time of occurrence, atmospheric and road conditions, the mechanical

Figure 1 Recontruction of an Accident

Picture by Krenz Engineering, LLC

Copyright 2008


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systems of the vehicles (brakes, lights and the type of tire); the drivers age, physical and mental

status and any disability will allows us to study the way the vehicle reacted in the occurrence.

Also all of the geometric road design parameters such as road width, number of lanes, curbs, plus

the constitution of the road and shoulder which include the condition of the asphalt, concrete or

gravel; soft or hard edges of the shoulder or no shoulder at all. Another guide that is used in the

recollection of evidence in a vehicular collision is to begin with the location of the resting points

of the vehicles, point of impact, accident debris, and skid marks; and if anybody was ejected

from any of the cars involved.

The use of photographs and video files allows having a clear shot of everything that

surrounds the scene; making sure to get all details that you might consider important and any

other thing that you do not consider of significance as it may be of use later in the development

of the case. The forensic surveyor must frequently rely on the skills of a police officer to provide

information about the accident in a proper perspective as well to focus on the evidence that

should be collected and the methodology implemented. Their inclusion is often beneficial and to

never forget that people provide parole evidence and in the forensic compilation

Methodology

In forensic surveying there are several methods that can be executed in order to obtain the

details for the reconstruction of an accident. One of the first things that a forensic surveyor must

do is take pictures of the vehicles or any other object that might be removed for precaution. A

picture is worth a thousand words is a popular saying and most of the time is true. Often expert

are asked to analyze an accident months or years after it occurred. In such a complex case and

sophisticated techniques involving computer are used to measure and gather the necessary data.


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Various computer programs aid the field experts with photogrammetry and three-dimensional

analysis. Besides photographs, a video camera is ideal to have so you may film everything

including the path taken by the vehicles involved in the collision.

The most crucial step is the gathering of the evidence in a scene. Evidence will include

the stories of witnesses and drivers, street signs, etc. After photographs have been taken, it is

now time to begin taking measurements between object found in the crime scene and permanent

landmarks in the crash site so that an arbitrary coordinate system may be established. Making a

traverse for control may also prove helpful when beginning with the reconstruction of the

accident. It will help to make an accurate reference frame of the data and measurements

collected. Once the reconstruction of the crash scene has been finished it will be used in court or

any other place that it might be needed. The forensic surveyor can be called upon to give his/her

impartial statement based only on evidence.

When the site has been altered, an inspection and detailed measurements can reveal the

information that has been covered up or lost. The basic geometry of the site is rarely altered. The

road curvature, super elevation, width, curbs, drainage, and many other features are rarely

altered. In the case where police, adjuster of witness photographs are available, photogrammetric

techniques can be employed to uncover some of the lost information. A simple ruler, tape

measure, or roller tape is invaluable in measuring many characteristics of an accident site or

vehicle dimension. Depending on the investigation and the object to be measured, it will tell us

the precision that will be needed. In case of measuring a skid mark; you need a precision the

closest foot as the calculation it will not matter. Another case would be to measure the distance

from axis to axis in a car that has been deformed or compacted from the impact; a precision of


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going to the nearest inch is good enough for the purpose of significance of the speed of the crash

and any number of forces involved.

When it comes to the specification of building, there is long list of thing to check. First of

all is the boring, which has to be at least 40 feet deep or have an area of 2500 square feet for a

building having four or more floors. Physical and laboratory tests should be done to verify that

the soil is adequate for the foundation. The concrete and steel work is checked, as once that they

are in place; any corrections will be difficult and costly. After that comes all the concrete and

steel structure for the finishing of the building.

The two major methods of surveying are three dimensional surveys which take into

account the theoretical shape of the Earth and cover large areas of land; and two dimensional

plane surveying which assumes that the survey area is a flat plane, generally covers small areas,

and is the most common practice method. Other cases for forensic surveying besides accidents

scenes are in the boundary of public and private properties, and overseeing all the phases during

the construction of a building, confirming all the dimensions and the right direction of the walls

and floors. For boundary laws for properties there are many different cases. One of those would

be that of two adjoining properties in which one of the owners has entered into the property of

another. A different case can be the construction of a building, house or any other structure near

a body of water, without leaving a required distance. Some other job cases for the surveyor are

the retracement of the boundaries with additional detail, a survey showing the contours of land

and locating the natural and manmade features above and below ground, and in construction is to

locate the horizontal and vertical control and alignment which helps the construction of public,

private, and utility improvements to the property.


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Instruments and Technology in Forensic Surveying

Over the years one of the struggles faced by the survey profession has been that only a

few people in the general public really understand it. Surveying professionals are finding that

technology is finally making a favorable public recognition. Of all of the positive applications

for surveying, the one that seems to have influenced the most is forensics. This use has been

drawn into the public eye from incidents like the investigations of Princess Diana's car crash, the

London subway bombings of 2005, major train wrecks, and many more. These technological

innovations are of great importance for all kinds of accident reconstruction including fires and

explosions, homicide scenes, engineering, structural failures, aerospace accidents, automotive

accidents or any other happening that private investigators need to document. There are a variety

of technologies for digitally acquiring the information required to properly reconstruct an

accident scene.

Laser Scanning

Laser Scanning is the process of shining a structured laser line over the surface of an

object in order to collect 3-dimensional data. Structured-light 3D scanners project a pattern of

light on the subject and look at the deformation of the pattern on the subject. The surface data is

captured by a camera sensor mounted in the laser scanner, which records accurate dense 3D

points in space. (www.dirdim.com) Measurements are recorded from a laser light that reflects from

objects after being projected from a series of rotating mirrors.


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The light beam travels from the electronic unit

(Fig.2, A) and hits the mirror (Fig.2, D), which is rotating

with large velocity. On the surface of this mirror the beam is

reflected and exits the laser scanning device with a specific

angle (Fig.2, B). Once the laser beam has finished scanning

all the objects between this angle , the upper part of the

scanner (Fig.2, C) rotates with a very small angle ()

around the vertical axis in order to start capturing the next,

adjacent elements. (Laser Scanning: A New Method for Recording

and Documentation in Archaeology) The laser calculates the

distance of a surface by measuring the time it takes a pulse of light to travel from the instrument

to the surface of the object and back. The amount of time before a detector sees the reflected

light is timed. Since the speed of light c is known (299,792,458 m/s), the round-trip time

determines the travel distance of the light, which is twice the distance between the scanner and

the surface. Iftis the round-trip time, then distance is equal to: .

The laser is low powered, so that it will not damage the object being scanned, and a

number of beams are shot at the object and recorded. The data from a laser scanning session

takes the form of a point cloud, which is a collection of very small data points used together to

map the object. In order to get a complete image, the scanner is moved around to cover all sides

and angles. The coordinates of the scan positions can be measured by using differential GPS or

any other surveying technique. Every point in the cloud of points is given by polar coordinates

(,,d), which each corresponding coordinates in the global system can be derived. Computer

Figure 2: Principle of a Laser

Scanner

*Image courtesy of Karl Kraus; LaserScanning: A New Method for

Recordin and Documentation in


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software combines the data together so it can then be used to create digital, three-dimensional

models useful for a variety of applications.

The recreation process has three consecutive phases (Fig. 3). First, the point cloud is

restricted to the area of interest by manual editing, so the number of points can be reduced (Point

Phase, Fig. 3, b). Once the unnecessary data is eliminated, the remaining points are thinned out

using curvature-based sampling, and triangulation (Polygon Phase, Fig. 3, c). Sometimes

manual editing of the triangulation is necessary in order to eliminate errors. The result is a three

dimensional image that provides a delineation of the geometric elements obtained by the

difference between the triangulated image and the point clouds (Shape Phase). (Laser Scanning: A

New Method for Recording and Documentation in Archaeology)

Through laser scanning data, prototype models, as shown in Fig. 4, are created. These

models can be used into the jury room as evidence to help explain the analysis of what happened

(a) (b)

(c) (d)

Figure 3: Laser Scanning Phases

(Fig. 3, a) Marc Anton sculpture at

the Viennese Secession.

(Fig. 3, b) Point Phase. Individually

colored point clouds as a result of

laser scanning from different

positions.

(Fig. 3, c) Polygon Phase.

Triangulated image

(Fig. 3, d) Shape Phase. Resulting

image. Difference: Original minus

Final.

*Images courtesy of Karl Kraus; Laser

Scanning: A New Method for

Recording and Documentation in

Archaeology.


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at the scene. For example, a car crash can be analyzed by

measuring the vehicle deformation, which helps determine

speed at impact and other contributing factors. Some of the

simulation programs use road and terrain contours to

determine the motion of a vehicle or even predict the

movement of a body within a vehicle as that body strikes

the interior contact surfaces.

Before the advent of laser scanning technology, forensic surveyors and engineers were

restricted to obtain no more than a couple of measurements per minute. With laser scanning,

surveyors are able to record 100,000 measurements every minute with accuracies up to +- 3 mm.

This technology has the ability to rapidly advance the field of forensics, not just in the area of

accident reconstruction but in any discipline that requires precision measurements. Details such

as roadway widths, lane lines, traffic signals, signs, utility pole lines, dimension of walls, as well

as each individual brick and the mortar between the bricks will all be recorded. It can provide

dimensional variances about underwater environments and surfaces, such as cracks or pits, not

previously available with traditional sonar and video. The study of tectonic and volcanic

processes at mid-ocean ridges, plate kinematics, mid-ocean ridge magma chambers, continental

margins, oceanic islands and the flexural and mechanical properties of the lithosphere are a few

of the many other ocean studies possible with this technology. In accident investigation, laser

scanning has so many advantages. Speed, safety, accuracy, comprehensiveness, and the ability

to return to the same data set and make new observations, serve well to forensic surveyors,

without the necessity of returning to the site of the event.

Figure 4: Prototype model of a car

accident scene generated from laser

scan data.

*Image courtesy NorthwayPhotomap

Inc.


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Total Station

A total station is an optical instrument used in modern surveying and by crime scene

investigators, accident recreationists and insurance companies to take measurements of scenes.

Using a total station to document physical evidence at critical accidents is fundamental for

forensic mapping. The system is divided in four main parts; a theodolite, the EDM (Electronic

Distance Measuring) instrument, the optical prism and a data collector. The theodolite measures

angles from magnetic north to points to be surveyed. The EDM instrument in most cases is a

pulsed infrared diode to read distances from the total station to a particular point. An optical

prism is used to reflect the light emitted from the EDM while the Data Collector captures the

measurements made. This data is later converted to produce either two-dimensional outputs

(maps, plans, building elevations, topographic surveys) or three-dimensional outputs (site

models) from which further interpretations may be made. The data may be downloaded from the

theodolite to a computer and application software will generate a map of the surveyed area.

Forensic mapping is often required to recreate a crime or accident scene or to verify that

measurements taken at the time of an event are consistent (Fig. 5). Usually survey data may seem

hard to interpret from a CAD program, therefore it is better to convert it into a simplified

drawing (Fig. 6). Robotic Total Stations combine advanced imaging and high accurate

surveying, incorporating real-time field imagery with spatial data. It produces photography with

dimensions, which can be an alternative to laser scanning, and usually recognizes significant

features in the images.


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Photogrammetry

Photogrammetry is the art, science, and technology of obtaining reliable information

about physical objects and the environment through processes of recording, measuring, and

interpreting photographic images. (Elements of Photogrammetry) Photogrammetry has been used

successfully in traffic management and in traffic accident investigations. Its use in the later area

has the advantage that photographs overlook nothing that may be needed later to reconstruct the

accident, and it is possible to restore normal traffic flow quickly. Relevant applications of

forensic photogrammetry include forensic image analysis and authenticity, analysis of video

events, demultiplexing and clarification of security videos, identification of suspects and analysis

to determine if material has been deleted, added, altered or changed in the image.

This technology allows instantaneous recordings of dynamic occurrences on film.

Because a photograph takes three-dimensional elements and projects them on a flat plane, depth

information is lost. However by knowing some information about the camera that took the

photographs and by having more than one photo of the same object from different perspectives,

it is possible to gain some 3D information back. It is even possible to take measurements from a

Figure 5: Typical site survey.

*Image courtesy of Forensics

Figure 6: Simplified 2D drawing from Total

Station data.

* Forensics


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single photo as well, but there are some criteria that need to be met. Depending on the number

and the quality of the photos, different approaches to photogrammetric analysis can be made:

1) Several photos of the object to be measured need to be taken from different camera angles.

2) Some objects in the scene must have known reference dimensions or dimensions that can be

obtained after the photos are taken. 3) The object to be measured must be clearly visible in the

photos and has distinguishable features. It should not be blurred or out of focus. 4) The size of

the object to be measured needs to be sizeable relative to the entire photograph. 5) Photos must

be taken with the same camera and same focal length setting. (www.ai2-3d.com). Each approach has

its advantages in accuracy and simplicity. The accuracy of measurements is limited by the size of

the photo and by how well the objects appear in it.

Regardless of the situation,

photogrammetry can be used to determine:

blood spray patterns, skid mark measurements,

crush measurements from a damaged vehicle,

measuring distances or measuring the height of

a suspect in a security video (Fig. 7). 3D

scanning with photographs is a very common

option to taking measurements of very complex surfaces. It consists of making 3D images out of

several photos of a single object taken from different angles. Footprints, vehicles or terrain can

be scanned by taking photos with a digital camera and accurately marking the object or scene

with a reference measurement. Once the same points of interest are defined, they need to be

referenced between all the photos. These points are then built up in 3D space using computer

software, which determines measurements, dimensions and coordinates between points.

Figure 7:Suspect's height determined through

photogrammetric techniques.

* Forensics


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Another technique used in photogrammetry is called image rectification, which is the

process of making equivalent vertical photographs from tilted photo negatives. Rectified photos

are used for the preparation of controlled mosaics and photomaps. Such photos have practically

no relief displacements and their scale is nearly uniform throughout if the tilt displacement is

eliminated. Rectification may be used to correct aerial photographs, remotely sensed data or

analogue maps.

Multiple images are

necessary in order to get more

accurate results in forensic

investigations. When these

photographs are taken from

multiple angles, the camera axes

are not parallel; therefore their

associated epipolar lines are

unparallel to the scan lines, which

cause the element of perspective.

The process of rectification for a pair of images transforms the original pair to another pair such

that the resulting epipolar lines are parallel and equal along the new scan lines. For example, skid

marks on a road are hard to study in regular photographs. If the position of four points or more

are known on the flat surface the image can be transformed so as to obtain a perfect plan view of

the surface. The transformation embeds the geographic coordinates onto the satellite data and

converts the data so that it will overlay with a known planimetric grid. This allows precise

(a)

(b)

Figure 8: Rectification

example.

a) Original image. The

positions of the fourcorners of the road are

used as reference for the

transformation required.

b) Rectified Image. A

plan view is now

obtained. Objects out of

the four selected corners

will be distorted.

Measurements can only

be made inside the

selected plane.

*Images courtesy of

ww.csse.uwa.edu.au


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integration with other geographically registered data. This technique helps forensic surveyors

and private investigators to make direct measurements from the rectified image (Fig.8).

Remote Sensing

Although the application of unclassified remote sensing images to accident and criminal

investigations has been limited, they have proven to be useful for documenting international

atrocities in areas that are inaccessible to outside observers. Sufficiently detailed satellite

imagery has been used to document international crimes such as possible genocide in the Darfur

region of Sudan. Also gravesites in Iraq were identified with the help of satellite image and aerial

photograph interpretation and then investigated in more detail using ground-penetrating radar

and other methods. Publicly available Land Sat satellite images obtained in 2003 and 2004 was

also used to document the burning of 44 % of the villages in the Darfur region of Sudan during a

period of civil strife, which some observers believe amounted to genocide. (www.enotes.com). The

affected areas where identified by the amount of radiation reflected by the ground surface since it

changed significantly during the times at which the two images were obtained. This was

accomplished by using a computer algorithm to calculate albedo from the satellite data, then

subtracting one albedo map from the other to calculate the change. The most common

multispectral images consist of some combination of red, green, blue, and near infrared bands.

Image analysts use information about the spectral reflectance of different kinds of soils, rocks,

and plants, to identify specific targets.


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Forensic Photography

Documentation of evidence is important in many aspects of a case, from simply recording

the condition of evidence to enhancing details that may not be discernable to the human eye. In

most cases evidence is documented only to save a record. In such cases the items are placed on a

seamless background, evenly lit and the entire piece of evidence is photographed. Some items

require close up photographs to document aspects of that evidence that may be important to a

case, especially bloodstains or cuts in clothing. It is also important to photograph evidence when

it will undergo changes during analysis, where trace or biological evidence will be removed for

further analysis. Not all evidence can be seen with the human eye, so several tools are used to

aid the search for evidence. Photography of this kind involves choosing correct lighting, accurate

angling of lenses, and a collection of different viewpoints. Scales are often used in the picture so

that dimensions of items are recorded on the image. Special light sources are often used to see in

alternate spectrums. Some items of evidence, due to their small size, require special techniques

for documentation. Photomacrography, which is the use of a bellows or extension tubes between

the lens and camera to increase magnification, is useful for documenting bullets and headlamp

filaments. Photomicrography (photography through a microscope) is often used for

documentation of trace evidence such as paint chips, hairs and fibers. Like all evidence a chain

of custody must be maintained for crime scene photographs. Sometimes a crime scene

investigator will process his own film or there is a specific lab for it. Regardless of how it is done

any person who handles the evidence must be recorded. Accident scene pictures should also be

identified and sourced, police photographs taken at the scene often being used in civil cases.


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Safety considerations

The field of surveying presents many challenges regarding safety in our workplace at all

times, but especially when we are dealing with forensic surveying cases related to accident

scenes. In such cases the surveyor has to go further in the approach taken regarding safety at the

time of doing his fieldwork. First because we as forensic surveyors must protect every piece of

evidence found at the site that can be significant in our case analysis and also since our

workplace is always moving, we need to secure our wellbeing at every time.

When working on a roadway, the survey party needs that all

members should make themselves as conspicuous as possible by

always wearing fluorescent colored shirts, vests, or jackets. These can

be considered a requirement since the working crew needs to be easily

identified by the roadway users. Other essentials equipment needed

also are survey crew signs, barriers, hard hats and safety cones that have the purpose of alerting

the drivers.

Survey equipment in use should be made as noticeable as

possible by the attachment of brightly colored bunting. If you are

placed in a situation where a vehicle may strike the survey

equipment, you may have a strong impulse to attempt to rescue it,

but in that case dont go for it as it may be too dangerous for

yourself. If anything happens the instrument can be repaired or

replaced, but your safety is far more important than the instrument

itself.

Figure 9: Survey Crew Sign

Figure 10: Fluorescent Vest


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When a survey party is working along a roadway, there is the ever-present danger of being

struck by a vehicle. In the midst of such a variety of dangers, the only way to prevent injury is to

be continually aware of the hazards around you. Every person in a survey party must be alert of

all existing hazards, be able to recognize an unsafe situation approaching, and be trained to take

appropriate preventive measures.

As much as possible, work should be scheduled during times when traffic is the

lightest. Work during rush hour on a metropolitan highway, for instance, would be so dangerous

as to be not feasible, in case that an accident occur in that time,

we should use the Temporary Traffic Control specified on the

Manual on Uniform Traffic Control Devices for streets and

highways, 2009 edition (MUTCD) made by the US Department

of Transportation. The MUTCD explains the correct procedures

that need to be applied on how to modify the roadway in case of

accidents, constructions or special cases when is necessary to

alter the original roadway.

In order to take preventive measures and react before its to late it would

be appropriate to use adequate markers, cones, and traffic warning

signs, such as ''Survey Crew Ahead", "Work in Progress", "Reduction

of Lane Ahead", should be placed where they will be highly visible and

most effective in warning drivers approaching or entering the work

zone. Always look to deviate traffic away from the survey party. If

deviation requires two-way traffic on a single lane, a flag bearer must be posted at each end of

Figure 11: Manual on UniformTraffic Control Devices

2009 Edition

Figure 12: Construction

Surveying


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the lane.

In case of construction sites the surveyor as well as other workers must follow the safety

measures provided by The Occupational Health and Safety Act (OSHA) that in essence

guarantees the safety of employees of construction sites. This includes using all the correct

equipment for the construction area, being aware of the heavy equipment around, and watching

the step every time.

When the work turns out to be in a criminal scene, we should be extra cautious and wait for

the proper local or federal authorities to clear the area of any exposure to danger, thus then with

the approval of a police or prosecutor we can start doing our technical work of collecting the

proper data.

These recommendations can be used by not only forensic

surveyors, but can also be used by any professional involve in the

surveying field, since our work is highly involved with dangerous

situations that put our lives at risk, thats why we need to act at all times

in a defensive attitude, and with an alertness of every aspect of the

environment around you.

Figure 13: Safety Traffic

Cone


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Forensic Surveying: A Look Ahead in the Future

This branch of surveying has grown quickly, mainly because its many applications have

shown the high-quality results and advantages it can bring to professionals of other fields. As

people begin to discover the uses of forensic surveying, this can dramatically change the way

people think about handling accident scenes, knowing that they can obtain a professional

scientific explanation of all the details regarding their study case analysis.

Looking ahead on what to expect in the future is necessary to point out that all these

achievements have been possible thanks to the new era of technology. This powerful tool has

successfully help the surveyors take full advantage of the conditions and elements exposed at

different sites. Having the possibility of obtaining a huge amount of data in a significantly less

time saves an enormous amount of work and money, allowing you to focus on other important

details in the investigations. Robotic technologies have made facilitate the collection of data.

Professionals of the field can anticipate in the future many challenges and new

developments to come as technology amaze us and help us achieve things never thought of.

Certainly this is going to evolve as one great field of research in science, because it gives us the

chance to offer the end users all the information in a accurate way, in such short periods of time

if the adequate technology is at hand.


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References

AI2- 3D. Forensic Mapping with Total Stations Samples. Retrieved February 7, 2010.http://www.enotes.com/forensic-science/remote-sensing

AI2- 3D. Forensic Photogrammetry Introduction Samples. Retrieved February 7, 2010.http://www.ai2-3d.com/SiteSamples/PhotogrammetrySamples.htm

Alameda, Jose I. & Lara, Juan (2008). Costs of Traffic Accidents in Puerto Rico.(Essaysand Monographies: Number 138). Economy Investigation Unit, Economy Department ofUniversity of Puerto Rico. Retrieved March 1, 2010.http://economia.uprrp.edu/Ensayo%20138joseialamedayjuanlara.pdf

Batterman , Scott & Batterman, Steven (2006).Forensic Engineering. RetrievedFebruary 4, 2010.http://www.ablminc.org/Model_Curriculum_LMME_2010/BOOK_Legal%20Medicine-7th_2007/Ch65-Forensic%20Engineering.pdf

Brown, Curtis M., Robbillard, Walter G. & Wilson, Donald A. 4th ed.(2002) Evidenceand Procedures for Boundary Location. New York: John Wiley& Sons, Inc.

Car-Accidents.com. Car Accident Statistics. Retrieved March 3, 2010. http://www.car-accidents.com/pages/stats.html

Direct Dimensions, Inc. Terminology. Retrieved January 15, 2010.http://www.dirdinm.com/lm_terminology.html

Federal Highway Administration. Manual on Uniform Traffic Control Devices (MUTCD)(2009). Retrieved February 4, 2010. http://mutcd.fhwa.dot.gov/

Franck, Harold and Darren Franck. (2010) Mathematical Methods for accidentreconstruction: A Forensic Engineering Perspective. USA: CRC Press.

Glassey, R. William (2004). Survey Safety. Retrieved November 18, 2009.http://www.lsaw.org/media/pdf/surveyors_safety.pdf

Hicks, Joel T. (2001). Traffic Accident Reconstruction. In Carper, Kenneth L. (ed.),Forensic Engineering (pp 129-156). Florida: CRC Press LLC.

Myers, Todd R. (2005). Surveyors-What are the and why you may need them . Angle andLine.Retrieved February 10, 2010.http://www.cowanassociates.com/ps_image/pdf/jannewsletter.pdf


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National Society of Professional Surveyors. Professional Surveyors Have Many Options.Retrieved March 1, 2010. http://www.surveyingcareer.com/careers/construction.html

Occupational Health and Safety Administration (OSHA). Retrieved February 4, 2010.http://www.osha.gov/

Van Kirk, Donald J.(2001)Vehicular accident investigation and reconstruction. USA:CRC Press.

Vozikis, George, et. al (2004). Laser Scanning: A New Method for Recording andDocumentation in Archaeology. Workshops Archeological Surveys. Retrieved January15, 2010. http://www.fig.net/pub/athens/papers/wsa1/wsa1_4_vozikis_et_a.pdf

Wilson, Donald A. (2008) Forensic procedures for Boundary and Tidal Investigation.New Jersey: John Wiley& Sons, Inc.

Wolf, Paul R.Elements of Photogrammetry. McGraw-Hill, Inc. 1974

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