Ge 178 lecture 7 (flight planning)

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