Survey GCP (Ground Control Point) Android tool

On the first release of Droidplanner I introduced a tool to help with the placement of Ground Control Points (visual markers placed on the field for aerial photogrammetry purposes). But on DroidPlanner 2 this tool has been removed, because it didn't really matched the idea of the rest of the application.

So for those how missed the tool (I'm sure not many), I forked the old DroidPlanner code into this new app leaving only the GCP related code. The same license applies (GPLv3) as in the old code, any any patches are welcome (but I don't think there will be much activity). 

The operation is simple:

  1. Load a KMZ or KML file from Google Earth with Placemarks where the control points should be.
  2. Lockup your location at the blue dot.
  3. Go to a GCP location at a Red dot
  4. Drop a GCP marker on the ground
  5. Click on the red dot of the GCP to turn it blue, to show that that place has been marked.
  6. If there are more red GCP then go back to step 2.

To use your own KML or KMZ file you must save them into your Android device storage, under the folder "/DroidPlanner/GCP/". The files can be created with Google earth, using just standard markers. As an alternative you can try to open a kml/kmz inside android (for example in a email attachment) and chose to use Survey GCP to open that file. (Note: there is a bug in the Nexus 7 where it doesn't load the file correctly from email attachments).

You can download it here.

And get the source here.

If you feel like donating to support the development go here.

Views: 4581


Developer
Comment by Jason Short on March 27, 2014 at 10:13am

Arthur, How or why would someone use Ground Control Points?

Thanks!


Developer
Comment by Arthur Benemann on March 27, 2014 at 10:39am

@Jason Short:

GCP are the reason I started developing droidplanner ( during the first week it was only the GCP tool), so I though they would deserve not to be forgotten ( the code would get lost since we are moving to DPv2). It was Chris suggestion that I forked that feature in a separate app.  Now to your questions:

Why?

When doing aerial photogrammetry, the use of visual markers on the ground with know coordinates can increase the accuracy of a generated orthorectified image or DEM. From experimental results with a APM system (old oilpan board) I built the accuracy was increased from ~2m RMS to ~0.2 RMS. And for some industries that accuracy is very important (e.g. mining).

How?

The GCP can be natural features of the landscape, but normally those don't offer enough contrast to be correctly identified, also you can't count on having the landscape at your favor. So the solution is to use artificial markers ( I have used white pizza boxes as a very cheap and light-weight marker).

The problem structs when you are on a big area and have to properly place those markers more or less in a grid, it's hard to know where to place them. Knowing what markers you have placed is also though, and the best route to make ( I'm assuming you are on foot).

Note however that this app isn't designed to capture the GPS location of the markers, just to aid in their placement. To collect the coordinates you need a proper GPS (I haven't tested the increase of precision using a phone GPS, but it will be a lot worse than what you get with an expensive GPS system).

Comment by OuBen on March 27, 2014 at 5:44pm

cool

Comment by benbojangles on May 11, 2014 at 9:03pm

Interesting. I just learned what photogrammetry is and what it is used for. Just wondering if multispectral sensors are possible?


Developer
Comment by Arthur Benemann on May 11, 2014 at 9:10pm

@benbojangles: Multispectral sensons are possible. But that's not what this app is used for, this one is for aiding in the placement of GCP. Which in turn could be used to georeference a multispectral image.

Comment by Darius Jack on January 4, 2016 at 9:03pm
@Arthur,

just installed your great Survey GCP app on Android tablet 10 inch, 4.2.2.
Installed, app stopped when started every time.
This is no-GPS tablet.
Does it matter from the start ?

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