Terrain Height and Overlap Setting Incorrect?

Correct me if I’m wrong but the field of view of the ground on a given camera is going to be 50% smaller if you fly at half the altitude. So the area of the ground captured at 100ft altitude is going to be 50% of the area captured at 200ft.

If you go into DroneDeploy, and create a mission (Mavic 2 Pro Drone), 39 acres for this example, 200ft AGL, default overlap of 65% sidelap, 75% frontlap, it gives you 491 total photos.

Now if you turn on terrain mode and tell it the tallest feature above your launch point is 100ft, essentially the software (assuming you have terrain follow turned OFF) has to then basially assume you are flying at 100ft AGL instead of 200ft since there are elevation rises as high as 100ft within the mission.

When you do this, it changes the overlap to 80% sidelap, 85% frontlap with a totla of 1443 images I don’t see how that could be correct.

Wouldn’t the equivalent overlap at a mission flown at 100ft be half the overlap if flown at 200ft and would result in the same number of photos? Why on DD does it go from 491 images to 1443 images on a 200ft mission when you turn terrain mode on with 100ft highest ground elevation?

I think this has something to do with the area is actually the factor of elevation change squared. So flying 50% lower, the width and height of the frame is going to be 1/4 the length bt the

I’m not understanding this part. With terrain awareness on it doesn’t matter where you take off because the flight plan is going to attached the drone to the surface model instead of where you takeoff from. You set the AGL as always and it follows the surface model. This adds waypoints at the grade breaks but I have never seen it change the photo count. There’s no need to change any other settings as you will be flying a true number to whatever you input as if it was a flat field making the GSD more consistent.

I don’t know of a setting where you tell it anything about the tallest feature? What you do have to watch out for is trees or buildings that are obviously not going to be in the surface.

Go to the web planner, and scroll down where you can select Terrain, Buildings, etc. Click the Terrain, it will then prompt you to enter the highest point of the terrain.

I believe I figured out the discrepancy. Although the ground field of view X/Y is halved if you fly half as high, the area is the square root. So if a flight at 100 ft requires 400 photos, a flight twice as high at 200ft requires 100 photos, not 200, given the same overlap.

Drone Deploy’s Terrain Setting is using what I call “fuzzy logic” in changing the overlap in terrain mode.

You’re thinking I’m talking about Terrain Follow. I’m talking about this:


Oh, now I see. That’s the old “terrain mode” in the sense that it is trying to calculate the best set for terrain values. I thought you were talking about the Terrain Awareness function just left of the main flight altitude… Personally I wouldn’t use that app for anything other than a hack of crosshatch. We like it because it allows you to set the gimbal pitch. IMHO there’s no reason to run more than 80/70 overlaps at any time. All it’s doing is adding unneeded data and processing time. We default to 80/65 and will sometimes drop to 75/65 if the situation allows. I have no idea of what theory the overlap calculations were according to back then.

Yeah, there is absolutely no reason to run more than 80 overlaps.

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