GE 178 Lecture 7: Planning Department of Geodetic Engineering University of the Philippines Diliman jldfabila ’09 japrincipe ‘10 Flight
Jan 14, 2015
GE 178 Lecture 7:
Planning
Department of Geodetic Engineering
University of the Philippines Diliman
jldfabila ’09
japrincipe ‘10
Flight
Project Planning
• Successful execution of any photogrammetric project requires thorough planning
• Must first determine the selection of products to be prepared, their scales and accuracies
aerial photo prints, photo indexes,
photomaps, mosaics, orthophotos,
planimetric maps, topographic maps,
cadastral maps, digital maps, digital elevation models
Project Planning
After the product selection process,
–Planning the aerial photography
–Planning the ground control
– Selecting instruments and procedures necessary to achieve the desired results
– Estimating costs and delivery schedules
Flight Planning
• Success of photogrammetric project depends on acquisition of good quality pictures
• Due to weather and ground conditions, time frame for photography is limited
• Reflights are expensive and causes long delays on project
• Mission must be carefully planned and executed according to flight plan
• Consists of flight map, (where photos should be taken) and specifications
Specifications
• Camera requirements
• Film requirements
• Scale
• Flying height
• End laps, side laps
• Tilt and crab tolerances
Stereopair
• Each photo covers partially the same area
overlap
photo 1
photo 2
Neatmodel
• Area of the overlap bounded by the principal points of the consecutive photographs
overlap
photo 1
photo 2
Neat model
Overlap
• Forward overlap or End lap – Common area covered by two successive photos of
the same flight line or strip
– Usually 60% ± 5%
• Lateral overlap or Side lap – Common area covered by two adjacent flight
lines/strips
– About 25-30% ± 10% (generally 30%)
Overlap Direction of
flight
Forward
overlap/Endlap
Lateral
overlap/Sidelap
Flight lines
Forward Overlap
• If stereoscopic coverage is required, 50% is absolute minimum
• To prevent gaps due to crab, tilt, flying height variations, terrain variations, >50% end lap is required
• For photogrammetric control extension, points must be seen on at least 3 photos
Side Lap
• Required to prevent gaps between flight strips
• Using side laps >30% eliminates the need t ouse extreme edges of photo
• Crab – disparity in the orientation of camera in the aircraft with respect to aircraft’s actual travel direction; causes the edges of the photo to be unparallel to direction of flight; reduces stereoscopic coverage
• Drift – failure of the pilot to fly along planned flight lines
Flight Plan
• What the aircrew has to do as indicated by flight lines
• The design of aerial photography flight in order to obtain desired photos at a certain scale, i.e., how the air crew will fly (where to put the flight lines, how high, etc.)
Rules in determining flight line direction
• Generally follows four cardinal directions – East-West (E-W) or North-South (N-S)
• Should be along the longer dimension of the area
• If over mountain ridges or valleys, go along the direction of the features – to maintain an almost constant scale; if a flight line crosses mountains, scale will be smaller in the valley than in the mountains
Direction of Flight Lines
Cordillera
Sierra Madre
Flight lines along the valley
Weather Conditions
Flight crew should be able to interpret weather conditions and make sound decisions on whether to fly or not
• Ideally cloud free; < 10% cloud cover acceptable • Clouds higher than the flying height might cast large shadows
on the ground • Overcast weather might be more favorable when large-scale
topo mapping is done over built-up areas, forests, canyons or other features which cast shadows on clear sunny days
• Photos for industrial areas susceptible to atmospheric haze, smog, dust and smoke are best taken after heavy rains
• Windy days might cause excessive image motion and difficulties in camera and aircraft orientation
Required Data for Flight Planning
• Project area boundary
• Camera focal length – 3.5”, 6”, or 12”
• Photoformat size – standard is 9” or 23 cm
• Photoscale
• Overlap requirements (in percentage) – percentage of endlap or sidelap
• Least number of flight lines
• Least number of exposures To be more
economical
Flight Planning Computations
• Flying height
• Distance between exposures or Airbase (B)
• Distance between flight lines
• Total number of exposures
• Flying height above mean sea level of each flight line
• Total time needed for photography
s
f
Hmge
S
o
s = photoformat/size
f = focal length
Hmge = flying height above
m.g.e.
o = overlap in %
S = equivalent ground
distance of photoformat
Flying Height
mge pH f s
Distance Between Exposures
1exp eD D S f .o.
Where:
S = equivalent ground length of the photoformat
size (s)
S = (sp)(s)
f.o. = forward overlap (in decimals)
s = photoformat size
sp = photoscale factor
Distance Between Exposures
Example:
Given:
scale = 1:15,000
f.o. = 60%
s.l. = 30%
s = 9” = 23 cm
Required: De
Distance Between Exposures
Solution:
kmD
mcmD
D
e
e
e
38.1
380,1000,138
)60.01)(23)(000,15(
Distance Between Flight Lines
1fl fD D S s.l.
Where:
S = equivalent ground length of the photoformat
size (s)
S = (sp)(s)
s.l. = sidelap (in decimals)
s = photoformat size
sp = photoscale factor
Distance Between Flight Lines
Example:
Given:
scale = 1:15,000
f.o. = 60%
s.l. = 30%
s = 9” = 23 cm
Required: Df
Distance Between Flight Lines
Solution:
kmD
mcmD
D
f
f
f
42.2
415,2500,241
)30.01)(23)(000,15(
Total Number of Exposures
total number of exposures
number of exposures per flight line
number of flight lines
Total Number of Exposures
Where:
longer dimensionnumber of exposures per f.l.
longer dimension
shorter dimensionnumber of flight lines
shorter di
e
f
D
B
D
mension
W
Flying Height of Each Flight Line (above Mean Sea Level)
msl mgeH H m.g.e
Total Time of Photography
number of exposures per f.l.
number of flight lines
eDt
v
Where:
time between exposureseDt
v
Total Time of Photography
Example:
Given:
scale = 1:15,000
f.o. = 60%
s = 9” = 23 cm
average velocity of aircraft = 300 kph
20 exposures per flight line
10 flight lines
Required: t
Total Time of Photography
Solution:
min2.55
92.01020300
38.1
38.1380,1000,138
)60.01)(23)(000,15(
t
hrst
kmmcmD
D
e
e
Example
A project area is 16 km long in the east-west direction and 10.5 km in the north-south direction. Aerial photography of scale 1:12,000 will be used with end lap and side lap of 60% and 30%, resp. A 6-in focal length camera and a 23-cm square photo format is to be used.
Prepare the:
– flight map on a 1:24,000 base map
– compute the total number of photographs needed
Solution
• Align the first and last flight lines with 0.3S (side lap dimension) coverage outside the north and south project boundary lines
• Equivalent ground distance of the photo format and distance between flight lines
mcmS 2760000,12*23
mlsSD f 1932.).1(
Solution • Distance of the first and last flight lines inside
North and South boundaries:
mmSSS 5522760*2.02.03.05.0
• Number of spaces between flight lines:
59.4
2.0*2toupround
D
Swidth
f
• Number of flight lines:
61spacesofnumber
Solution • Adjust the percent side lap (for integral # of
flight lines)
widthprojectSls
spacesofSls
100
..1#
100
..5.02
mmls
mls
105002760100
..152760
100
..5.02
%4.31.. ls
• Adjust spacing Df:
mSD f 4.1893100
4.311
Solution
• Distance between exposure De:
mSDe 1104100
601
• # of photos per strip (take 2 extra photos at both ends):
)20(5.192211104
16000use
m
m
Solution
• Total # of photos:
120)6)(20())(#( linesflightofstripperphotos
• Spacing of flight lines on map:
cm9.710024000
4.1893
END OF LECTURE