Flight Planning for Aerial Photography.

[SwampDonkey]

Ever wonder how it's done?  I promise, it's not rocket science. ;)

Here is an example.

I have a study area over Doaktown, NB of 4 km wide in the east - west direction and 4 km long in the north - south direction (yellow lines on Map 1 below). Up is north. A camera having a 152.4 mm focal length lens and a 230 mm (9" x 9") format is to be used. The desired photo scale is 1:10,000 and the nominal endlap and sidelap are to be 60% and 30 %. Beginning and ending flight lines are to be positioned along the boundaries of the study area. The only map available to me for the area is at a scale of 1:50,000. This map indicates that the average terrain elevation is 90 m (300 feet) above sea level. Now, lets do the necessary computations to develop a flight plan and draw a flight map.



Map 1

[SwampDonkey]

Flight direction will be west - east.

Now we will find the flying height above the terrain and add the mean site elevation to find flying height above mean sea level:

Flying height = focal length + avg elevation
                     target scale 
                   = 0.1524 m + 90 m
                        _1   
                        10,000 
                   = 1614 m


Now determine ground coverage per image from film format size and photo scale:

coverage per photo = 0.23 m
                               _1   
                               10,000 
                             = 2300 m on a side.

Determine ground separation between photos on a line for 40 % advance per photo (60 % endlap):

0.40 x 2300m = 920 m between photo centres.

Let's assume we are flying the aircraft at 160 km/hr, the time between exposures is:

= 920 m/photo X 3600 sec/hr
   160 km/hr       1000 m/km
= 20.7 (use 20 secs) because the intervalometer can only be set in even seconds, the number is rounded down, so 60 % coverage is ensured.

Now we have to recalculate the distance between photo centres, using the reverse of the previous equation:

= 20 sec/photo X 160 km/hr X 1000 m/km
                                         3600 sec/hr
= 889 m/photo

[SwampDonkey]

Now we need to compute the number of photos per 4 km line by dividing this length by the photo advance. Add one photo to each end and round the number up to ensure coverage:

= 4000 m/line  + 1 + 1 = 6.5 photos/line (use 7)
   889 m/photo
If the flight lines are to have a sidelap of 30 % of the coverage, they must be separated by 70 % of the coverage.

0.70 x 2300 m coverage = 1610 m between flight lines

Now we need to find the number of flight lines required to cover the 4 km study area width by dividing the width by distance between flight lines. (this gives number of spaces between flight lines, add 1 to arrive at the number of lines):

= 4000 m width + 1
   1610 m/line 
= 3.48 (use 4)

The adjusted spacing between lines for 4 lines is

= 4000 m
   4-1 spaces
= 1333 m/space

Find the spacing of flight lines on the map (1:50,000 scale):

1333 m X _1 mm 
              50 m
= 26.7 mm

Find total number of photos needed:

7 photos/line X 4 lines = 28 photos



Map 2 Flight plan map

[SwampDonkey]

The resulting mosaic of aerial photos was used to produce this distortion free orthophoto. Photo centres are shown on the flight lines.





Note: the photo centres marked here are for demonstration purposes, not the actual locations, but can be obtained by NBDNR as a GIS layer or paper map.

[LeeB]

I'm really it's you that's doing this SD. It makes my head hurt.

[John Mc]

Swamp Donkey -

Are you a pilot? If so, what are you flying?

John Mc

[SwampDonkey]

John, no. But, I have been a passenger in a few small planes and commercial ones.  Don't count I guess. ;)

[jim king]

SwampDonkey:

Why are you taking the photos  ??

[SwampDonkey]

Jim, I'm not. It's just an information sharing exercise on the procedure. However, flight planning is done this way for forestry and agricultural mapping among other uses.

One of them slow moments, needed something to do. ;)

[jim king]

One of them slow moments, needed something to do.

I can relate to that.  Sitting here like a toad in front of the computor is getting old fast.

[tonich]

SwampDonkey,

The last time I did it, was when I was a student.  :
However, we use such photos and remote sensing now and then, when we do surveying for the decade management plans, which are mandatory in Bulgaria.

[SwampDonkey]

It's done here all the time for forestry and agriculture. But, the market is so limited that the chances of any forester being involved is like winning the lottery. And it's done by companies from out of province, so that cuts down on anyone from NB ever being involved substantially.

[tonich]

Same in Bulgaria. I do not know of  any forester involved in this matter. 
I don't think I will ever come to developing another flight plan, after the one I did in the University.

[Tom]

I've discovered that I am capable of doing absolutely nothing.

[Mooseherder]

I've been flight planning the last couple nights on Google Earth. ;)
Last night I did a tour of the Cape Verde Islands.  Very interesting from a Bird's Eye view.
I've been visiting Canada tonight.
There's no snow on the ground yet. ;D

[Samuel]

It's done here all the time for forestry and agriculture. But, the market is so limited that the chances of any forester being involved is like winning the lottery. And it's done by companies from out of province, so that cuts down on anyone from NB ever being involved substantially.

We fly our blocks every year and then convert them using soft copy where the blocks are analyzed and the retention is counted to determine if we are on track or not.  We will most likely be utilizing this technology within the next 12-18 months to conduct our regeneration surveys also.

[SwampDonkey]

I didn't know that was the software. They call them softcopy distortion free aerial photos when you down load them off Service NB. I'll have to Google it. I thought the term softcopy was the term used to produce the orthographic projection using computer software and digital map layers to make corrections to distortions with known (X,Y,Z), not the actual software name.

I see that is is case after Googling a couple USGS sites.

I guess I mis-understood your post.

[Samuel]

The way I understand it, the program "softcopy" digitizes the aerial photo and then the gurus do thier magic on it.