### Calculating ground GPS coordinates of photo taken from UAV

When you take a picture from a UAV how do you go about figuring out the GPS coordinates of the area in the photo - I don't want/need the GPS of the UAV but want the coordinates in the photo itself?  I'm not quite sure where to find more information about this - any pointers?

#### Replies

• What you are trying to achieve is not possible without an accurate ground terrain surface model for the photo area. Have a look at software such as Photomodeller or iWitness to see how it can be done. Their method is to use 2(or more) overlapping pics and given 3(or more) known coordinates in the pics you can easily determine the cords of any photo location. There is a cost involved.
I am curious as to what we are really trying to achieve and why.

The issue is not about getting the GPS coordinates of the UAV at the time of the snap shot - thats easy - what I'm after is calculating the actual photo boundary when it may be at a distance from the UAV.  just for sake of argument lets say the UAV is flying at 60,000 feet and the camera angle from the plane is 45degrees of compass angle and 45 degrees down angle.  Assuming that the picture in the image is of the ground the image would be several miles away from the UAV itself - but if I know the GPS coordinate and dead reakon position of the UAV I should be able to also calculate the dead reakon alignment of the camera and from there it should be possible to calculate the geoboundary of the patch on the ground - but thats where the math gets more complicated as you have a 3d line in space that passes through the ground at some distance away from the UAV - that distance can be used to calculate the width of the picture at that distance as well as the skew angles at the corners, etc - I would just think that all of these calculations had already been worked out somewhere as its all really just basic 3d trig.  So far I haven't been able to find anything in google searches probably because I don't know how to describe this particular problem is something different than basic photo mapping - but even basic photo mapping has some of the same problem - i'd define basic photo mapping as those where the camera is pointing directly down so as long as the pitch, yaw and roll of the UAV are 0 the GPS of the UAV is the center coordinate of the picture - but you'd still need to know both the altitude of the plane and altitude of the ground to calculate the boundary coordinates unless you could get a reading that was your altitude above the ground which seems unlikely.

I don't plan on flying a UAV at 60,000 feet but even at 500 feet its easy for a UAV to take a picture of something that is several hundred meters away from the location of the UAV - again its that location that I want not the GPS location of the UAV.  Any ideas how to do that or is there any software that does this?

• If you're using a standalone camera, perhaps matching photo timestamps with your telemetry log?  This isn't a fun answer but it might be the quickest route.

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