Flight Planning (Photogrammetry)

7/25/2019 Flight Planning (Photogrammetry)

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Flight Planning

Presented by-

Praveen Meena

14520012

Geomatics engi

M.Tech 1styear


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What is flight planning ?

It is one of the three basic phases of planning for a photogrammetr

Three phases of planning a photogrammetric project are:-

1. development of a flight plan.

2. planning the ground control and executing necessary field surve

accuracy requirement of the project.3. estimation the cost involved in the project.

To produce a map of the desired accuracy.

Finding out the best fit flight lines and camera exposure stations to

project area with minimum number of models, flight lines and cam

exposure stations.


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Basic elements in flight planning:-

The flying height above a datum.

The ground distance between successive exposures.

The ground spacing between the flight lines.


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Why we need flight planning in

photogrammetry?

To ensure coverage of the area to be mapped at the required scale w

and provide stereo models by an efficient design.

A flight plan will determine the spacing between successive photog

location of flight lines and other details.

This entails the preparation of detailed instructions for the plane-c

regarding the location of the pictures, the flight strips, and the area

This is also important for a safety flight , reducing aerial survey ope

costs, and speeding up the preparation and execution of the photo m

flight.


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Flight planning or flight design depends

on the following factors:-

The intended use of the photography:-

Mosaic, land-use study etc.

Map compilation using stereo plotting equipment.

The exact boundaries of the project.

The nature, extent, and location of existing control.

The type of terrain.


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Factors for plannig the flight map:-

Purpose of the photography The ground distance between successive exposures

Ground spacing of between the flight lines

Flying height above a datum , usually sea level

Photographic scale

Allowable scale variation

Relief displacement

Photographic Tilt

Crab and drift

Direction or orientation of the topography or terrain


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Steps for flight planning:-

Determining of the project requirements. Considering the requirements of the project , project area, photo sc

side lap, direction of strips, coordinate system, camera type, and film

determined.

According to these data, base distance between two exposure st

flight line and the distance between two adjacent flight strips are The flight height is calculated for each strip by checking the terra

related strip.

After that, coordinates of exposure stations are obtained.


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Purpose of the photography:

Wide or normal camera types are selected according tocharacteristics of the project area.

Wide length cameras (f= 152mm) are preferred for the area that is

smooth.

In order to obtain a favorable base height ratio that enhances vertical

accuracy.

Super-wide angle (f=88mm) camera:- if the topography is very flat.

Normal lens (f=210mm) cameras are preferred for the area that is

hilly or urban area. eg. Forest area..

It will also determine the %age of overlap and sidelap.


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Photo scale:-Varies with the project.

Scale =

=

It affects the map accuracy and area

configuration.

Longer the f, the larger the scale,

assuming a constant flight height.


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The scale of a vertical aerial photograph is inversely proportional t

quantity (H-h), i.e. high altitude photographs are normally small sc

Scale not only differs from photograph to photograph and strip to s

the average scale can differ somewhat from what is intended.

Photo scale is selected depending on the project purposes, such as

accuracy of final product, purpose of use etc.

The smallest possible photo scale is selected because of reducing tmodels.


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End lap and side lap:- Overlap :- the overlap in the along the line of sight is called forward

or simply overlap.

In order to obtain stereo model, end lap is assumed to be 60 %.

To cover the project area completely with stereo models along the s

side lap is assumed to be 30 % of the width of the photograph.

if the terrain is fairly rugged, both overlap and sidelap should be in


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Allowable scale variation:-

Scale variation in a photograph or between photographs is

caused by variation in the ground elevation, by a variation in

flying height, or by both.

Variations caused by difference in ground elevation and

flying height.

Longer focal length reduces the scale variation.


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Flying height:-

Height above the datum.

Factors affecting the flying height:-

Desired scale, relief displacement, and relief.

Precision of scale used

Greater precision, greater possible flying height, and that w

also increase the ground coverage per photography four tim

More the flying height, greater the area covered, and thus less gro

control and fewer photos required.


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C-factor =

( precision factor)

from which,

Flying height = (contour interval) X (C- factor)

WHY CONTOUR INTERVAL ?

Because vertical accuracy in a topographic map is the liming factor in

photogrammetry.

The C factor is understood to be that value which will produce photography

satisfactory to obtain the desired vertical accuracy In the map.

C factor take ib values anywhere from 750 to 2500 ( mostly 2200)

For a given system, its value will depend on the conditions surrounding the

entire map-compilation operation.


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Relief displacement:-

It affects the construction of mosaics.

it is a characteristic of aerial images over varied terrain.

Objects that rises above the surface lean away from the principal po

Objects extending below the surface lean towards the principal poi

Relief displacement increases with the height of the object and/or d

from the principal point.

It will decrease as the flying height is increased.

Also, to maintain a certain scale as the flight height is increased, the

length must be increased.


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=

=

=

and =

=( )

and R =

Relief distortion = =

=

()

= =

=

RD is radial from nadir point regardless of

unintentional or accidental tilt of the camera. This

is a fundamental concept of photography.


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The effect of tilt:-

Two component:-

1. the amount in the direction of flight, called y-tilt, or angle

.2. the amount in the direction of the flight line, called x-tilt or ang

y tilt will cause increase or decrease in overlap between successiv

photographs.

X tilt will cause the sidelap to increase on one side of the flight lin

decrease on the opposite side. Causes of tilt-

The absence of stable horizontal reference plane during flight.

Human error in holding the camera in the only available reference p

Air turbulence.


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The effect of y tilt on overlap must be allowed for by decreasing

the computed exposure interval slightly to produce a slightincrease in the theoretically desired overlap

The effect of x tilt on sidelap must be allowed for by decreasing

the computed spacing between flight lines slightly to produce a

slight increase in the desired sidelap.


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Crab

crab is the angle formed between the flight line and the edges of the photograph

in the direction of flight. it will reduce the effective width of coverage of the photography .

it is caused by not having the focal plane of the camera squared with the

direction of flight at the instant of exposure.

It can be corrected by the rotation of camera about the vertical axis of the

camera mount.


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Drift

It is caused by the failure of the aircraft to stay on the predetermined flightline.

It will cause in loss of sidelap on the side

opposite the direction of drift.

It will cause gapping in between adjacent

flight lines.


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Computation of flight plan:-

Data required to compute different quantities for flight

planning of an area are:-

1. focal length of the camera lens

2. flying height above a stated datum.

3. Size of photograph.

4. Size of area to be photographed.

5. Position of the outer flight lines with respect to the boundary of the area.

6. Overlap.

7. Sidelap.

8. Scale of flight map.

9. Ground speed of aircraft.


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Problem:- An area that is 15 miles long in the north south d

and 8.5 miles wide in the east west direction is to be

photographed with a lens having a 12-in. focal length for

purpose of constructing a mosaic. The photograph size is

in. The average scale is to be 1:12,000 effective at an averelevation of 700 ft above sea level. Overlap is to be at leas

and sidelap is to be at least 35%. An intervalometer will b

to control the interval between exposures. The ground sp

the aircraft will be maintained at 150 mph. The flight line

be laid out in a north south direction on an existing map han scale of 1:62,500. The two outer flight lines are to coin

with the east and west boundaries of the area. Determine

for the fight plan.


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FIG. Calculation of flight plan


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Flying height:-

we know that scale = focal length / flying height

i.e.

(7) =

So, H= 12,700 ft above sea level.

Ground distance between flying lines:-

the ground spacing, W=. . ,

./ = 5850


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Number of flight lines:-

Width of the area = 8.5 miles X 5280 ft/mile = 44,880 ft.

Required number of flight lines = number of spacings + 1

=,

+ 1 = 9

Adjacent ground distance between flight lines:-

Wa =,

= 5610

the sidelap will be slightly greater than 35%

Spacing of flight lines on flight map:-

Wm = , 12 = 1.08

Ground distance between exposures:-

since 60% overlap is there, the net gain per photograph = 0.40 x 9 in. = 3

The corresponding ground distance is,

B =. ,

.

= 3600 .


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Exposure interval:-

Speed of aircraft = 150 mph =

= 220 ft/s

The required exposure interval is,

I =

/= 16.4 s or 16 seconds

Adjusted ground distance between exposures:-

for the adjacent exposure interval, the ground distance is,

Ba= 220 ft/s X 16 s = 3520 ft

Number of photographs per unit flight line:-

total length of a flight line = 15 miles X 5280 ft/mile = 79,200 ft.

lets make allowance for two extra exposures at each end of each strip,

the number of photographs per flight lines is,

7,

+ 4 = 26.5 or 27 photos/flight line

Hence entire photography will require, 9 X 27 = 243 photographs.


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Hence,

Number of photographs required = 243 photographs

Flight lines spacing on map = 1.08 inch

Exposure interval = 16 seconds

It will ensure the required overlap of 60 %.


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THANK YOU

Documents

Flight Planning (Photogrammetry)