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Lecture 4 - 1 - 10/23/2003 ____________________________________________________________________________________
Concept Hell/Pfeiffer February 2003 ___________________________________________________________________________________
4. Principles of Picture taking 4 hours Aim: principles of picture taking (normal case, convergent for point measurements, flight planning) flight planning (parameter, photo scale, cameras, instruments for outer orientation) ___________________________________________________________________________________ 4.1. Planning of terrestrial photogrammetry
Depending on the position of the camera we could divide photogrammetry to ground, aerial and
space. The ground photogrammetry is divided to terrestrial and close range photogrammetry.
The case of the close range photogrammetry is when the distance to the registered object is less
then 300m (in some sources no more then 100m). Close range photogrammetry includes three
main areas of application: architectural (and archeological), civil engineering photogrammetry,
industrial photogrammetry, medical photogrammetry (biomedical or bioengineering). Some
special parts of architectural photogrammetry could be separated as civil engineering
photogrammetry, when object of measurement are special engineering objects and constructions,
that are not buildings like bridges, roads, airports, tunnels, hydro technical objects, Other special
purposes of close rage photogrammetry are criminology, road accidents, micro photogrammetry.
Terrestrial photogrammetry is generally associated with objects distances in excess of 300m.
Another distinction between two categories is the fact that in terrestrial photogrammetry cameras
are focused to infinity while it is not the common case in close range photogrammetry. This type
of terrestrial photogrammetry is called also topographic terrestrial photogrametry (some times
phototopography). This is a science of surveying in which the detail is plotted entirely from
photographs taken at suitable ground stations. The photographs in terrestrial photogrammetry are
usually used for topographic purposes or for terrain modeling. They have large focal distances
and could be used for great distances to the objects. Cameras used for producing terrestrial
photographs are called terrestrial cameras or phototheodolites. Phototheodolites are combination
of theodolite and photogrammetric measuring camera in which the relationship between the
camera axes and the line of collimation of the theodolite can be measured. The single cameras
used in close range photogrammetry could also be used in terrestrial photogrammetry (when they
are usually focused to infinity).
For close range photogrammery is usually possible to determine more accurate the position and
orientation of photogrammetric cameras.
____________________________________________________________________________________ FH-KA - Master course Photogrammetry 2003 B. Marinov
Lecture 4 - 2 - 10/23/2003 ____________________________________________________________________________________
Depending on the relative orientation of main camera axes we have stereo couple with parallel
axes, with convergent axes (most often oriented to the center of the object) and with divergent
axes. This last case is usually applied when we have camera position inside of the object.
For stereo pairs, taken with parallel axes we have normal case, when axes are perpendicular to the
base, left or right tilted parallel photogrammetry.
Depending on the slope of camera axes we have cases of horizontal photos and sloped photos
(raised or dropped).
The most common use of close range photogrammetry is normal case. There are cameras
designed for taking only the normal stereo pairs (stereometric cameras).
b b
A
a ax
X
Y
O O
2
2
1
1
P
c
1
c
P2
B
Y0
x21 Figure 4.1. Normal case
The coordinate relations in normal case are very simple
____________________________________________________________________________________ FH-KA - Master course Photogrammetry 2003 B. Marinov
Lecture 4 - 3 - 10/23/2003 ____________________________________________________________________________________
1,
,
1,
.
AA a
Ax a
AA a
YX xc
B cYpYZ zc
=
=
=
(4.1)
where parallax , 1, 2,x A ap x x= − a
The derivation of error in distance direction Yσ as a function of base-length is shown in the
Appendix 1.
The length of base B is selected from the relation
max min
20 5Y B< <
Y (4.2)
For the tilted parallel case the camera axes are parallel each other but they are tilted at the angle
Φ. The geometry of this case can be related to the normal case with different value of base b.
Very often when it is necessary to produce a model of whole object the surrounding position of
capturing cameras is applied. In this case the adjacent cameras are with highly convergent axes
and stereo measurement is not possible. In this case the arrangement of cameras is made in such
way that it is a cameras in front of the main facades of the object. Similar situation is shown on
the figure below.
____________________________________________________________________________________ FH-KA - Master course Photogrammetry 2003 B. Marinov
Lecture 4 - 4 - 10/23/2003 ____________________________________________________________________________________
b
A
ax
X
Y
O
1
1
P
c
1
B
Y0
b
a
O
2
2
c
P2
F
F
F
x2
1
Figure 4.3. Geometry of parallel tilted case
The right station is displaced in Y direction on the value By
.cos .sinx yB B B B= Φ = Φ (4.3)
The geometry of tilted case is related to normal by substitution
2( .cos .sin )Bcb c x= Φ − Φ (4.4)
Substituting in co-ordinate equations we obtain
2
21
21
( .cos .sin )
( .cos .sin )
( .cos .sin )
Bc
A
Bc
A
Bc
A
c xbY cp p
c xX
pc x
c
x
Z zp
Φ − Φ=
Φ − Φ=
Φ − Φ=
(4.5)
For the convergent case of taken photos the camera axes are deflected in the opposite sides in the
way that they converge. This situation is shown on figure 4.3.
____________________________________________________________________________________ FH-KA - Master course Photogrammetry 2003 B. Marinov
Lecture 4 - 5 - 10/23/2003 ____________________________________________________________________________________
b b
A
a ax
X
Y
O O
2
2
1
1
P
c
1
cP2
B
Y0
x2
1
F1 F2 Yav
Figure 4.3. Convergent case
Some relations between average distance and convergent angle are given in the Appendix 2.
____________________________________________________________________________________ FH-KA - Master course Photogrammetry 2003 B. Marinov
Lecture 4 - 6 - 10/23/2003 ____________________________________________________________________________________
Figure 4.4. Cameras surrounding the object
In close range photogrammetry is not possible to define a scale that is equal for the whole object.
The scale is depending on the distance to the corresponding part of the object.
The expression for scale at fixed distance d is defined as follows
1'b
b
d Xmc x M
= = = (4.6)
____________________________________________________________________________________ FH-KA - Master course Photogrammetry 2003 B. Marinov
Lecture 4 - 7 - 10/23/2003 ____________________________________________________________________________________
d
c
PP 1
M = Mb1 b2
Figure 4.5. Cameras with different angle of view
Cameras with different frame format (different angle of view) but with equal camera constant
produce images whit the same scale from the equal distances.
For cameras with equal camera constants but different distances to the object the scales differ.
P
P2
1
M > Mb1 b2
c
c
d
d
2
1
Figure 4.6. Different distance to the object
In this case the scales for two distances are as follows
1 21 2 1 2 1 2 1 d dm m d d m m M
c c= = → < → < → 2M> (4.7)
____________________________________________________________________________________ FH-KA - Master course Photogrammetry 2003 B. Marinov
Lecture 4 - 8 - 10/23/2003 ____________________________________________________________________________________
Cameras with different camera constants produce images with different scale from the same
distance.
P
P2
1
M > Mb2 b1
cc
d d
2
1
Figure 4.7. Cameras with different camera constants
1 2 1 2 1 2 11 2
d dm m c c m m Mc c
= = → < → > → 2M< (4.8)
In case of usage the cameras with different camera constants it is possible to obtain the same
scale at the desired object plane if the appropriate distance to the object is set.
____________________________________________________________________________________ FH-KA - Master course Photogrammetry 2003 B. Marinov
Lecture 4 - 9 - 10/23/2003 ____________________________________________________________________________________
P
P2
1
M = Mb1 b2
c
c
d
d
2
1
2
1
Figure 4.8. Cameras with different constants may ensure equal scales
The condition for cameras with different camera constants to produce equal scales is the equality
of ratios d/c.
1 2 1 2 11 2 1 2
1 2 1 2 2 d d d d dm m m m
c c c c d= = → = → = → 2
1
cc
= (4.9)
The conditions for taking photos of the object could be select based on the above relations.
For every photogrammetric project the appropriate disposition of the cameras must be evaluated.
The disposition depends on the goals of the project and the required accuracy. For topographic
photogrammetry the full cover of the area under consideration is necessary. The camera axes are
Usually oriented through the structural lines of the terrain to ensure maximum visibility from
every station position. The vertical slope of the camera depends on the terrain height respectively
to the camera position. The camera positions are usually selected based on the planimettric
coverage of the area of mapping. The check for visibility is made after that.
For close range photogrammetry the camera positions are selected taking into account different
considerations. The main goal is to ensure coverage of the whole object with minimal number of
stations. From the other side it is necessary to ensure enough number of tie points between
photographs. They must be well visible in all the overlapping photos. Sometimes bad orientation
of some of the points gives as the final result pure estimation for point accuracy.
____________________________________________________________________________________ FH-KA - Master course Photogrammetry 2003 B. Marinov
Lecture 4 - 10 - 10/23/2003 ____________________________________________________________________________________
Figure 4.9. Close range photogrammetry project
Another problem is the selection of control points. Control points for close range
photogrammetry may be natural elements on objects – vertexes of the edges, small elements,
elements on the drawings or ornaments on the object. Some time it is possible to fixed signalized
control points at the suitable positions. Depending on the object this is always possible. After
signalizing the object the problem is exact positioning and orientation of cameras. For positioning
the cameras are used traditional survey methods. For orientation are usually used the supplied
____________________________________________________________________________________ FH-KA - Master course Photogrammetry 2003 B. Marinov
Lecture 4 - 11 - 10/23/2003 ____________________________________________________________________________________ instrument for angle measurements. For orientation of photogrammetric cameras is typical that
usually the angles of theodolite axes are known relatively to the camera axes. This angle is fixed
and after that camera is oriented by targeting to specified target on the object or on the tripod. For
vertical orientation are usually used bubble levels to ensure base vertical position of camera axis
of rotation during exposure. For near facades are supplied special adapters that allow to incline
camera vertically (upwards or downwards) at the fixed angles ( more often ±30 and ±70gon).
When for taking photos are used non-metric cameras without adapters for precise leveling and
orientation the more sophisticated procedures for processing are applied. In this case only the
observation of control point in the area of viewfinder is possible.
4.2. Planning and executing the Aerial Photogrammetric Project
4.2.1. Types of Aerial Photography Types of aerial photos are classified depending on the orientation of camera axes
Vertical case. The camera axes are vertical or near vertical. This is main often used case.
Advantages are:
- easy measurements;
- normal shape of images and easily recognition;
- less hidden ground objects.
Oblique case. The camera axes have greater angles relatively to horizon.
The oblique photography can be low-oblique or high-oblique.
Advantages are:
-coverage of large areas;
- increasing base-height ratio.
This photography is widely used for military purposes for reconnaissance.
Special case is horizontal photography. It is usually used for orientation of camera systems.
Non frame cameras usage. There are two main cases:
- panoramic cameras – slit is moving perpendicularly to the direction of light.
Special case of panoramic cameras is horizon-to-horizon camera.
- slit cameras – the slit movement is result of aircraft flight. The film is moving synchronous
with the projection of the ground at the focal distance.
____________________________________________________________________________________ FH-KA - Master course Photogrammetry 2003 B. Marinov
Lecture 4 - 12 - 10/23/2003 ____________________________________________________________________________________ 4.2.2. General requirements Aerial photogrammetry is widely used for purposes of mapping. The basic operations in
conducting a photogrammetric mapping are:
-Photography: obtaining suitable photography for mapping;
- Control: obtaining sufficient control through field surveys and/or extension by
photogrammetric methods;
- Map compilation: the plotting of planimetric and/or topographic features by
photogrammetric methods;
- Map Completion: the refinement of the map editing in the office and further, special
surveys in the field;
- Final Map Drafting: the completion of the map by drafting/scribing.
The first step, as given in the preceding outline is to prepare a complete plan that will make
possible to start the actual mapping operations and that will guide these operations as they are
carried out. The plan includes the following essential steps.
- Conversion of requirements: region to be mapped, the scale at which it is to be
mapped, the accuracy of he final map, the date by which the map should be
completed, the approximate cost of the project;
- Gathering of materials and people for the planning: photographs, maps, survey data,
instruments, and personnel;
- Determining Specifications and conditions for Operations: where to establish control,
how much photography is necessary, kind of equipment.
- Preparing Final Plans: scheduling, instructions for surveying, photography,
compilation, quality control;
- Costing and Replanning: redone the plan until costs are set within limits.
The information that is gathered at the second step of planning includes:
a) aerial photographs of the region to be mapped;
b) b) old maps of the region;
c) c) survey data showing the locations of horizontal and vertical control in region, the
accuracy of control and its accessibility.
4.2.3. Planning and execution of aerial photography project (flight planning) The aerial photography is base upon which the photogrammetric project is build. The success of
the project consequently depends greatly on the availability of suitable photographic coverage.
____________________________________________________________________________________ FH-KA - Master course Photogrammetry 2003 B. Marinov
Lecture 4 - 13 - 10/23/2003 ____________________________________________________________________________________ Suitable coverage of the project depends upon many factors of which several are of particular
importance:
a) scale of photographs;
b) overlap between exposures;
c) optical and mechanical characteristics of the taking camera;
d) film base and emulsion type used;
e) date of photography.
4.2.4. Flight planning Practical aerial photogrammetry is limited to the approximately normal case; but the exact normal
case cannot be achieved. The deviations of individual photographs from the strict normal case
are, in practice not more than Dw=±5 gon, DF=±3 gon and Dk=±15 gon. A tolerance of ±2% in
the flight height is usual. The track of the aircraft can, with visual navigation and good navigation
information, be held within ±1 cm in the photograph space.
The simple geometric relations required for flight planning are shown 4.9, where flat ground is
being assumed.
Figure 4.10. Flight plan
The relations between main parameters of flight project (according to Kraus) are formulated later
on. In formulas and figure 4.10 are used the following symbols.
A – Distance between flight lines B – Base c – Principal distance s – Image side (to edge) h – Flying height above the ground Z – Ground height
____________________________________________________________________________________ FH-KA - Master course Photogrammetry 2003 B. Marinov
Lecture 4 - 14 - 10/23/2003 ____________________________________________________________________________________
Z0 – Absolute flying height v – Flying speed over the ground L – Length of the strip or block Q – Side length of the block mm – Scale of mapping
The relations between parameters of flight project are defined.
Table 4.1
Photo scale number .pm k m= m k depends on apparatus
Flying height above the ground . ph c m=
Image side in the ground . pS s m=
Base in the photograph
p
Bbm
=
Absolute flying height 0Z Z h= +
Overlap between photos [%] .100 1 .100S B Bl
S S− = = −
Side lap (%) .100 1 .100S A Aq
S S− = = −
Ground area of one photograph 2 2.p p2F S s m= =
Base length for l% overlap . 1
100lB S = −
Distance between strips for q% side lap . 1
100qA S = −
Number of models in the strip .( /50 1) 1 for 50mL S ln l
B− − = + >
Number of photographs in the strip 1p mn n= +
Number of strips in a block 1 for 50s
Q Sn qA− = + <
Area of stereoscopic model ( )m .F S B S= −
New area for each model in a block .nF A B=
Time between photographs [ ][s] = 2/0 [ / ]B mt
v m s∆ ≥
____________________________________________________________________________________ FH-KA - Master course Photogrammetry 2003 B. Marinov
Lecture 4 - 15 - 10/23/2003 ____________________________________________________________________________________ [ ] – Largest integer number
The values of l and q are usually taken l=60% and q=30%. When GPS control is used for aircraft
tracking it is possible to decrease the values of overlap and lap but not too much due to the
requirements of triple overlapping in strip and overlapped tie points between the strips.
The value of side lap allows for:
• Errors in holding the track of the aircraft along the strip (~±5%)
• Variations in lateral tilt Dw (~±5%)
• Residual, uncorrected drift (~±3%)
• Variations in rotation of the photograph about its axis (~±3%)
• Smaller variations in terrain heights
Lightening of the image at the edges in electronic dodging, which make it impossible to observe
stereoscopically right to the edges.
By satisfying the above conditions it is possible to remain minimum 10% coverage of side lap
between strips, in which homologous points can be found to serve as tie points between strips,
and mapping is possible without gaps.
Flight planning is inseparably bound up with project planning. The particular points to be
observed are:
• The performance limits of the aircraft
• The ranges f the stereoplotter to be used
• The type of product – line map or photo map
• The ground relief
• The size of the map sheets of the finished product
• The accuracies required
Two methods are used to allow for the map sheet limits with Very good navigation data are
required for aimed photographs to ensure that the photographs really are aimed strip: aimed
single photography or a high overlap. A global positioning system is a very good help in this task.
If a high overlap is chosen, usual value of 90% and the best situated photographs and
stereoploters are then chosen.
A navigation plan is drawn up as part of the flight planning. This can consist either of enlarged
aerial photographs or better a good topographic map. The navigation plan must show:
The area of interest, which absolutely must be covered by stereopairs;
Any obstacles of flying;
____________________________________________________________________________________ FH-KA - Master course Photogrammetry 2003 B. Marinov
Lecture 4 - 16 - 10/23/2003 ____________________________________________________________________________________ Any prohibited areas, which are forbidden for flying or allowed under strict precautions (military
training areas, foreign countries).
The requirements to graphical presentation of navigation plan:
Area of presentation must be extended at least 5 km at each end of the strips, for turning of the
aircraft;
The flight line is shown with solid lines over the strips and with dashed lines for manoeuvres.
Each flight line is accomplished with notes on the flying height and course (azimuth in degrees)
at each end.
Additional information is given on separate sheet. It contains:
-Project name, purpose, dates,
-Photo scales, focal length, absolute flying height, overlap, side lap,
-Minimum length of film required and type of film;
Organization details:
-agreements on signalisation of points,
-closeness of international boundaries,
-flying only under full cloud cover.
The typical navigation and personnel equipment of survey aircraft includes:
• special glass of camera port or remotely operating camera;
• navigation instrument is inside with overlap regulator;
Central disposition of camera ports with possibilities to close the doors during take off and
landing
Good view downwards for the camera operator and possibilities for communication;
good navigation utility – GPS, Dopler or Inertial Navigation systems (INS)
Flight crew duties:
- pilot – coarse navigation;
- copilot – pilot support
- (navigator –navigation),
- camera operator – fine navigation and camera control.
4.2.5. Aerial camera equipment Modern aerial cameras are complex system. A schematic diagram of such camera is shown
below.
____________________________________________________________________________________ FH-KA - Master course Photogrammetry 2003 B. Marinov
Lecture 4 - 17 - 10/23/2003 ____________________________________________________________________________________
Figure 4.11. Camera equipment
Camera cycle (min 1.6-2.0 sec) includes:
exposure (with motion compensation), rising the pressure platen, releasing the vacuum
transport the film , advanced the photo number, apply the vacuum, press the platen.
Modes of exposure:
aimed single photograph – by operator control; serial photographs – with automatic overlap control
Content of the Viewfinder used for visual control:
-field of view with interchangeable frames, depending on objectives;
- level bubble;
- central cross of target point;
- set of moving eccentric spiral for overlap control;
- central line for angle orientation and drift control.
____________________________________________________________________________________ FH-KA - Master course Photogrammetry 2003 B. Marinov
Lecture 4 - 18 - 10/23/2003 ____________________________________________________________________________________
Figure 4.12. Navigation view-finder
If it exists wind during the flight, the aircraft trace on the ground does not coincide with the
direction of flight. By that reason the angle orientation of camera is due to be in the opposite
direction (but with the same size as) the angle aircraft flight according to the flight line.
The influence of the wind is shown on the next figure (according to Kraus K., 1983)
Figure 4.13. Drift compensation
____________________________________________________________________________________ FH-KA - Master course Photogrammetry 2003 B. Marinov
Lecture 4 - 19 - 10/23/2003 ____________________________________________________________________________________
v0 – vector of own velocity vw – vector of wind v – resultant vector of velocity over the ground
Some cameras have separated overlap regulator with viewfinder
Figure 4.14. Overlap regulator
Barometric differential height measuring device (statoscope)
The possibility to exposure the coordinates from navigation system (if persists)
Some cameras have unit for forward motion compensation.
Appendixes
Appendix 1
The derivation of error in distance direction Yσ as a function of base-length is shown below. It is
derived from the formula for Y coordinate in object space.
.x
BY cp
= (4.10)
The error in Y co-ordinate is function of the standard error of the parallax
____________________________________________________________________________________ FH-KA - Master course Photogrammetry 2003 B. Marinov
Lecture 4 - 20 - 10/23/2003 ____________________________________________________________________________________
2. .Yx
B cp pσ σ= (4.11)
The error is estimated for maximal distance because for it the error is maximal. From this error
the value of B can be computed.
2max( ) p
Y
YBc
σσ
=
(4.12)
The length of base B is selected from the relation
max min
20 5Y YB< < (4.13)
The stereo overlapping zone stats at the distance Y0 from the middle of the base and has wide-
angle 2.β. The distance of the vertex of stereo overlapping zone is defined by the equation
0 2 .cotBY gβ= (4.14)
As angle β could be expressed by photo size lx and camera constant c,
/ 2tan xlc
β = (4.15)
it is possible to obtain other presentation for Y0
02. .Y
x
c Bl
= (4.16)
Appendix 2
The length of base B and average distance Yav with overlapping of kov are connected with
relation
(1 ). .tan( ) (1 ). .tan( )ov av ov avB k Y k Yβ β= − + Φ + − − Φ (4.17)
The minimal distance at which the overlapping area begins is given by the equation
01 2tan( ) tan( )
BYβ β
=+ Φ + − Φ
(4.18)
____________________________________________________________________________________ FH-KA - Master course Photogrammetry 2003 B. Marinov
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