Uneven Terrain

[nwairphotos]

I'm going to be mapping a property that has some rolling hills. It's not laid out like my hypothetical below, but it's easier to explain this way.

Presume there is a square 9 acre property that is level except in the middle there is one acre that is a hill and the top is 60' higher than than the surrounding acres. Also there are 50' trees at the top and 50' trees on the lower flat acreage.

If I set up Map Pilot to fly at 100' AGL, will it clear the trees in the middle on the top of the hill? Will it follow the contours? Does is matter whether I begin the mission at the top of the hill or on the lower level?

 

[MapMaker53]

Unfortunately, the Phantom does not know the terrain like a cruise missile. It will generally consider your take-off point to be 0' AGL. But check to make sure your software resets the altitude at startup. Using your hypothetical, if taking off from the lowest terrain you would want to fly at greater than 110' AGL (60' + 50') in order to clear the hill it's trees. If you begin the mission on top of the hill, you would only have to set your flight to be greater than 50' AGL to clear the trees on the top of the hill.

 

[DefiantChild]

Map Pilot has a feature called terrain aware. I used it while mapping a 10 acre parcel about 3 weeks ago. Terrain aware will import and interpolate ground elevations (probably based on USGS or Google mapping API data) and adjust AGL accordingly. It does not, however compensate for trees, towers, or other structures.

So if you use terrain awareness, 100' AGL ought to work. If not, set RTH to 150' or 200' which should provide plenty of clearance if your bird has collision avoidance capabilities. Without terrain following you'll either need a flight AGL > 110' and/or you'll need to map your mission in such a way that your middle square is well in excess 110' AGL.

My personal opinion is that every photometric mapping drone app should provide terrain elevation tracking and compensation. But they don't. DroneDeploy does not provide terrain elevation tracking/compensation whereas Map Pilot does.

I personally experienced numerous in-mission Map Pilot app crashes compelling me to switch to DroneDeploy to map an unevenly graded 1,275 acre parcel with adjacent rolling hills. But DroneDeploy's failure to compensate for ground elevation changes was equally frustrating.

So I ended up sub dividing my missions into smaller grids and moved my home points as needed to maintain a relatively consistent AGL (so my image resolutions would be relatively consistent). But I had rolling hills to the west of the property and had to both fly higher and tighten my image overlap to avoid collision and ensure no photometric gaps in my map.

It was a challenge.

 

[doktorinjh]

every photometric mapping drone app should provide terrain elevation tracking and compensation

This is frustrating to see that app developers have worked backwards when it comes to waypoint control. The first DJI Ground Station app allowed you to set your AGL, speed, turn characteristics, and other control for each waypoint. For a sloping site, I had to add additional elevation for each waypoint, but it was fairly painless. It seems like the developers are trying to keep their liability down by taking control away from the end user, or maybe they're more focused on the photography side of things.

 

[DefiantChild]

Google's mapping API provides ground elevation relative to average sea level given a pair of correctly formatted geocoordinates. I presume their database is a derivation of the USGS repository.

If I recall correctly Google offers both a commercial and noncommercial license for access to the data. If companies like DroneDeploy do not want or cannot afford to license an enterprise API key, they could compell each individual subscriber to obtain their own individual key and allow altitude data for a mission to be pulled through their app.

What I'm saying is that there are solutions if developers want to avail themselves.