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Sep 21 2010

You've got to let the little guy's leash out!

This afternoon I worked with Nisarg to better understand how to setup a path for collecting aerial photos with the Hexakopter.  We quickly found that doing so would not be difficult and that adding our own custom waypoint list to the Mikrotool was straightforward.  However, during the fligh test we learned about an important setting to be aware of in the Navi-Ctl that really limited our test today.  By changing the settings as described below, we should be out flying over the entire Knoll in no time!  I think Nisarg is going to post later about the Mikrotool Map software that he was working with that provides an easy system for getting a Google Earth image into the Mikrotool OSD.


In testing our waypoint options, Nisarg was able to create an output text file (a .wpl file) of the Mikrotool OSD waypoints.  The file looks like this:


I looked at that and thought, “Well I can make that!” and set about generating a waypoint file over a route we wanted to fly for the Knoll site on campus in ArcGIS.  We had been discussing flight strategies and how to achieve image overlap and I showed Nisarg and Garrett a little bit of the kind of map making and simple spatial functions that can be done in ArcGIS: Garrett seemed more impressed than Nisarg.  I have been consulting Elements of Photogrammetry a lot recently for flight planning and also some simple calculations I made of the amount of overlap and area observed by a camera at a given height above the ground surface. I will be posting more about that later.

Anyway.  We came up with the a simple parallel grid track for the Hexakopter to navigate over the Knoll with 50m spacing between tracks.  I estimated that at about 70m altitude from the ground (@ Home) I would achieve the desired overlap even over the Knoll and trees. We went outside with the gear, climbed up to the top of the parking garage and went for it.  We also had a Garmin Edge GPS attached to the top of the dome to provide a track of where the little guy was going: not sure if the MKGPS can record tracks.  From the beginning it seemed like something was wrong.  It was kind of flying in the correct pattern, but it did not seem like it was going far enough across the forest.  We brought it back down and took a look at the GPS track.

As you can see in this somewhat messy image, the little guy did not go exactly where we wanted him to. 

A brief legend:

  • - Blue lines are the intended route
  • - Green dots are the intended waypoints given to the Mikrokopter
  • - House symbol is flight home
  • - Large yellow arc is a 250m buffer around the quad, more on this below
  • - Small yellow circle is a 100m buffer around fight home

So what happened?  The Hexakopter tried its best to fly those waypoints, but kept hitting an invisible wall and was forced to come back.  The units come preset with a GPS maximum range of 100m.  So our guy was flying his path, hit that 100m mark and was deflected along his route without hitting all the points.  Through a bit of research we came across the issue on the forums, http://forum.mikrokopter.de/topic-13563.html, and the solution on the Wiki (linked from the forums): http://www.mikrokopter.de/ucwiki/MK-Parameter/Navi-Ctrl_2 .

The units still will not fly beyond 250m with GPS with the current setup.  We thought that this was the default setting and hence set up our route to fly at max 250m across the Knoll from an intended Home in the quad, that is why the larger yellow arc is not centered. 

From here we are going to update the Navi-Ctl setting to allow us to fly to the max 250m from home and I am going to put together a small script in Python to turn an ArcGIS point file table into the waypoint format needed for the Mikrotool…but maybe not by Friday!

refs: Wolf, P., DeWitt, B., 2000. Elements of Photogrammetry with Applications in GIS 3rd Edition, McGraw Hill.