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Maximum Imagery Area Coverage

Discussion in 'Phantom 2 Vision + Discussion' started by MobileImageryDJI, Jan 14, 2015.

  1. MobileImageryDJI

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    Curious to know how far my conservative estimates are off if one were to fly to an altitude, snap a still and move onto an appropriate overlapping area to ensure proper orthomosaicing of stills (i.e. 2D map stitching). Came up with these off-the-cuff numbers but would be curious to know people's experience in one flight the area covered and the image ground sample distance equivalent of something like controlled image base (CIB) or MOBAC tiles - zoom level 19 and down.


    Thanks for any feedback.
     

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  2. IrishSights

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    DJIs PC Ground Station software does the basic calculations from entering lens and other parameters. However this does not take into consideration wind.

    Consider flying a grid, going one way against the wind, your speed is lower so using your pre determined interval will get a bigger overlap than on the return leg when you are traveling faster with the wind. On the return leg you could possibly get no overlap at all.

    What I do is set the camera to record in 4k at 15fps with moderate speed. Then in editing software write out single frames at what ever rate gives me desired overlaps. In my example above going slower against the wind I might save a frame every 1sec but on the bit of the clip on the return save a frame every 1/3 sec to get the same amount of overlap.

    With my GoPro 5.4mm lens I get the equivilent if around 8 mega pixel images per frame grab - which is OK. Hope that helps.
     
  3. herkam

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    If you use the ground station app you can get 16 waypoint which would give you 8 "legs" that you can shoot.
    It's a setback that you can't set the waypoint using coordinates in the app so you will have to make it as good as possible by hand.
    The upwind/downwind shouldn't be an issue since it uses groundspeed and not air speed for the set speed, so as long as it can keep up wind the set groundspeed against the wind it should be ok.
    If you use 8 m/s (is that the high speed setting speed?) and take a photo each 5 seconds at 100 m height would that give you enough coverage or do you need to use a slower speed or increase height?

    I have been looking at the software ImageJ (free ware) which has stiching capabilities and there you can also give the software the order of the pictures so it knows what pictures to try to stich together.

    /hakan
     
  4. IrishSights

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    I'm using the fully featured PC version not the app and each waypoint has lat and long that can be set. In practice it flys faster one way than the other...my experience. I use Agisoft Photoscan and the stitching is all automagic around 200 images at a time. As I'm using a GoPro they are not Geo tagged. I import the tiff into QGIS and use the Georeferencer Plugin to get matched ground points, then it becomes a georefed geotiff on a layer over Bing Imagery base map. Works for me.