civil and environmental engineering and geodetic science part v gps-supported mobile mapping...

Civil and Environmental Engineering and Geodetic Science

Part V

GPS-supported Mobile Mapping Land-based and Airborne

GPS/INS Integration for Direct Orientation (direct geo-referencing) of the Imaging Component of the

Mobile Mapping System

GS608


• A Mobile Mapping System (MMS) can be defined as kinematic platform, upon which multiple sensors have been integrated and synchronized to a common time base, to provide three-dimensional near-continuous and automatic positioning of both the platform and simultaneously collected geo-spatial data.

• MMSs are most commonly designed as modular systems that can be installed on various land or airborne platforms, and their components can be easily replaced by more advanced counterparts as technology progresses.

• The primary components of MMS are • the control module, • the positioning module and • the imaging module,

creating together a multi-tasking operating system, which provides automatic acquisition of directly oriented digital imagery for GIS and mapping data collection.


• The direct georeferencing or direct orientation (also referred to as direct platform orientation, DPO) is usually facilitated by the integration of Global Positioning System (GPS) in a differential mode and an Inertial Navigation System (INS), providing high-accuracy positioning and attitude (spatial orientation) information of the imaging sensor(s).

• While land-base MMS, usually driven at normal speeds, travels on a highway, city or a state road, the GPS/INS module collects positioning and attitude information of the image acquisition events.

• Real-time or post-processing of these data provides a directly georeferenced stereo-pairs (or multiple stereo-pairs per epoch if more than two cameras are used) in a selected mapping coordinate system.

• Oriented images are then used in a photogrammetric processing to extract the feature data together with their positional information. Features and additional attributes acquired this way can be directly transported to a GIS database, and stored there for an easy access.


• Significant Savings in Field Data Collection

Mobile Mapping ParadigmMobile Mapping ParadigmMobile Mapping ParadigmMobile Mapping Paradigm


Why GPS/INS Integration?Why GPS/INS Integration?

GPS and INS have complementary operational characteristics

• GPS contributes its white error spectrum, high accuracy and stability over time, enabling a continuous monitoring of inertial sensor errors

• Calibrated INS offers high short-term accuracy and high sampling rate

• INS is self-contained; no outages

GPS/INS offers a number of advantages over a stand-alone GPS

• immunity to GPS outages and reduced ambiguity search volume/time for the closed-loop systems

• and more importantly, continuous attitude solution

Implementation of a closed-loop error calibration allows continuous, on-the-fly (OTF) error update bounding INS errors, leading to increased estimation accuracy


Principles of Inertial NavigationPrinciples of Inertial Navigation Principles defined in the inertial, non-rotating frame

Real time indication of position and velocity of a moving vehicle using sensors that react on the basis of Newton’s laws of motion

these sensors are called Inertial Measurement Units (IMU)

• accelerometers

sense linear acceleration in inertial frame

does not sense the presence of a gravitational field (rather the reaction to gravity field)

• gyroscopes (sense rotational motion)

facilitate the rotation between navigation and INS body frames (in fact rotation with respect to the inertial frame is measured)

Integration with respect to time of the sensed acceleration to obtain velocity, and subsequent integration to obtain position


Inertial Navigation System (INS)Inertial Navigation System (INS) Provides self-contained independent means for 3-D positioning

Three gyros and three accelerometers (or less)

Accuracy degrades exponentially with time due to unbounded positioning errors caused by

• uncompensated gyro errors

• uncompensated accelerometer errors

• fast degradation for low cost INS

High update rate (up to 256 Hz)

Mechanical (stabilized platform) systems

• sense acceleration in inertial frame coordinatized in navigation frame

Strapdown systems (digital)

• sense acceleration in inertial frame coordinatized in body frame


-Y

-XZ

INS LN-100 Body AxesINS LN-100 Body Axes


Direct Orientation Land-based Direct Orientation Land-based SystemSystem

• For precise spatial positioning


Direct Orientation Land-based Direct Orientation Land-based SystemSystem

Digital camera

GPS antenna

INS


Imaging PC

GPS Base Station

BigShot™ Hasselblad Camera

Trimble 4000SSI

LN-100

INS/GPS PC

GPS Antenna The Center for Mapping is focused primarily on spatial data technologies, including precise navigation and georeferencing by means of GPS and INS, and has received international acclaim for pioneering work on the land-based mobile mapping system, GPSVan, followed by the Airborne Integrated Mapping system (AIMS) – a high accuracy GSP/INS positioning system, supporting primarily digital image data collection. The system currently comprises two dual-frequency Trimble 4000SSI GPS receivers, a medium-accuracy strapdown Litton LN-100 inertial navigation system, and a digital camera based on a 4,096 by 4,096 CCD with 60 by 60 mm imaging area (15-micron pixel size), manufactured by Lockheed Martin Fairchild.

AIMS™ Hardware ConfigurationAIMS™ Hardware Configuration


Georeferencing: the ConceptGeoreferencing: the Concept

Sensor orientation, also called image georeferencing, is defined by a transformation between the image coordinates specified in the camera frame and the geodetic (mapping) reference frame.

• requires knowledge of the camera interior and exterior orientation parameters (EOP)

• interior orientation: principal point coordinates, focal length, and lens geometric distortion are provided by the camera calibration procedure (describes the camera geometry)

• exterior orientation: spatial coordinates of the perspective center, and three rotation angles known as , , and


Direct GeoreferencingDirect Georeferencing

ZBIN

S

XBIN

SXC

YC

YBIN

S

ZM

XM

YM

rM,k

rm,i,j

rM,INS– 3D INS coordinates in mapping frame

– 3D object coordinates in model frame (derived

from i,j stereo pair) attached to C-frame

– 3D coordinates of point k in M-frame

– boresight matrix between INS body frame and

camera frame C

– rotation matrix between INS body frame and

mapping frame M, measured by INS

– boresight offset components

– scaling factor

BINSjimBINSC

MBINSINSMkM brRsRrr ,,,,

MBINSR

BINSCR

BINSb

rM,INS

rm,i,j

rM,k

s



Traditional aerial surveying

• EOP determined from the aerotriangulation, defining correlation between ground control points and their corresponding image representations

• requires scene pre-targeting

• high cost

• labor intensive



Modern aerial surveying

• EOP determined directly from integrated sensors such as GPS/INS or GPS antenna array

• no scene pre-targeting (no ground control, except for GPS base station)

• no aerotriangulation

• low cost

• allows automation of the data image processing


Planning

¦ Date¦ Time¦ Scale etc.

Compilation and Editing

DistributionAerial Photography

Cost

CartographicFinishing

Aerotriangulation Compilation Reproduction

Aerial PhotographyGround Control Film ProcessingPlanning

¦ Date¦ Time¦ Scale etc.

A Comparison of Mapping Scenarios

Conventional

Direct OrientationCost

Cost


Land-based Mobile Mapping: An Land-based Mobile Mapping: An Example Example


Street & Asset InventoryStreet & Asset InventoryStreet & Asset InventoryStreet & Asset Inventory

Lane Width/CountLane Width/Count

Heights/OffsetsHeights/Offsets

SidewalksSidewalks

PavementTypes & Conditions

PavementTypes & Conditions

Signs & Signals

Signs & Signals

ClearancesClearances


Field ProceduresField Procedures Field ProceduresField Procedures

• Two GPS base stations– Quality control– Datum, map projections, heights

• Quality Control points– Independent check of system accuracy

• Feature Input– Voice recording


Utility Pole InventoryUtility Pole InventoryUtility Pole InventoryUtility Pole Inventory

type of poletype of pole

height of conductorsheight of conductors

offset between cablesoffset between cables

coordinate locationscoordinate locations

image of featureimage of feature


• Street Map• Facility Records• Digital Images

Visual Management of AssetsVisual Management of AssetsVisual Management of AssetsVisual Management of Assets

utility poleutility pole

cable location


Asset Location & InventoryAsset Location & InventoryAsset Location & InventoryAsset Location & Inventory


Stereo-MeasurementStereo-Measurement

STESTEreo reo PPositioning ositioning SSystemystemTMTM


Workflow ApplicationsWorkflow Applications


Traffic Sign InventoriesTraffic Sign Inventoriessign typesign type

height above pavementheight above pavement

offset from road edgeoffset from road edge

coordinate locationscoordinate locations

size of signsize of sign


System AccuracySystem AccuracySystem AccuracySystem Accuracy

• Accuracy better than 1 ft (horizontal)

• Influences on accuracy

– GPS blockage - foliage, bridges

– Base stations

– Distance from cameras

• Typical fit to ground truth • on average 2-20 cm for flight altitude ~ 300m

• 0.2-3 cm for land-based applications (10-20 m object distance)

GPSVanGPSVan

AIMSAIMS


Product QualityProduct Quality Product QualityProduct Quality

• Turn Key System– Asset Inventory

– Database Management & GIS Software

– Linking Legacy Databases

• High Position Accuracy

• Color Stereo Image Database

• Multiple Attributes for each Record


Your Opportunity for the FutureYour Opportunity for the Future Your Opportunity for the FutureYour Opportunity for the Future

• Geographic Information System– Road Centerlines

– Digital Image Logs

– Asset Inventory

• Infrastructure Management– Managing Assets & Work Flow

– Linking Legacy Databases

• Total Solution


Customer Benefits: GPSVanCustomer Benefits: GPSVanCustomer Benefits: GPSVanCustomer Benefits: GPSVan

• 10:1 Savings in Data Collection

• 10:1 Reduction of Field Trips

• Pro-active Maintenance of Assets

• Improved Customer Service

• Increased Productivity


How Does it Work? Airborne System AIMSHow Does it Work? Airborne System AIMS

• Independent imaging sensor calibration (indoor test Independent imaging sensor calibration (indoor test range)range)

• GPS/INS/imaging sensor are mounted on the airborne GPS/INS/imaging sensor are mounted on the airborne platformplatform

• System calibration must be performed on a specialized System calibration must be performed on a specialized test rangestest ranges

• boresight calibration (outdoor test range)boresight calibration (outdoor test range)

• lever arm (INS GPS antenna separation)lever arm (INS GPS antenna separation)

• Airborne mapping missionAirborne mapping mission

• GPS base and rover receivers are turned on first GPS base and rover receivers are turned on first

• INS is initialized with GPS-provided coordinates of the INS is initialized with GPS-provided coordinates of the starting positionstarting position

• GPS/INS are turned on and work continuously; imaging GPS/INS are turned on and work continuously; imaging sensor collects data in automatic or user triggered mode; sensor collects data in automatic or user triggered mode; exposure times are registered exposure times are registered


How Does it Work?How Does it Work?

• Data are post-processedData are post-processed

• GPS and INS data are time-synchronizedGPS and INS data are time-synchronized

• These data are processed by the Positioning ModuleThese data are processed by the Positioning Module

• Positioning Module output: X, Y, Z and three attitude Positioning Module output: X, Y, Z and three attitude angles for the epochs of image collection (continuous angles for the epochs of image collection (continuous trajectory at 1-256 Hz is also provided)trajectory at 1-256 Hz is also provided)

• Positioning Module output can be directly used on a Positioning Module output can be directly used on a softcopy system to process the image data to produce softcopy system to process the image data to produce asset maps, topographic maps, etcasset maps, topographic maps, etc

civil and environmental engineering and geodetic science part v gps-supported mobile mapping...

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