Hi,
I bought this quadcopter : https://store.3drobotics.com/products/diy-quad-kit. Now, I'm looking for a camera to do 3d mapping like here : http://copter.ardupilot.com/wiki/common-3d-mapping/ . I seen canons, with CHDK are used. I seen this tutorial http://copter.ardupilot.com/wiki/common-chdk-camera-control-tutorial/ . I think a Canon S100 will be good to do what I want but I have some question.
Why do I need a controlled camera? A camera which take a picture every X seconds is not enougth?
Agisoft PhotoScan allow to add GPS points. Is it better and is it possible with the Pixhawk and the Canadon S100? Is there a tutorial to do that?
Is there better then the Canon S100?
If you have some tips on this subject, I am interested.
Replies
The external trigger serves one or two purposes, depending on the camera you have:
1. It can control the exact time you take a picture. So if you fly fast or slow, you take the right number of pictures as specified by your overlap settings.
2. If your camera doesn't have GPS, it can insert the CAM lines from the log into the GPS EXIF data of each photo, which is then extracted by the processing software. If you have GPS, then it doesn't matter that much.
If you use an intervalometer you thus get less control over where each photo is taken, so you may get a situation where you have too little overlap and you get holes in your orthophoto or model. You can of course give it a try anyway, because you can use the GPS control features to position and orient the model/orthophoto correctly. those softwares have tutorials out that explain how to do this.
Is it important to have exact position or interval of images? In this video : https://www.youtube.com/watch?v=wBKidr0e-XA it seems to recognized where the images are took. I tried it and it seems to work. What are advantages to add position?
If you don't have positions of the photos nor ground control points, the mesh or "photo" that it creates is not geo-referenced. So, it could be anywhere in the world. It's still a valid photo or a model though, just not related to any place in the world.
GeoTIFF files have this geo-referenced information inside them, so when you open them in GIS they fall into place where they are actually located in the world.
If you use the GPS positions in the photos, then you don't have a lot of precision, but it's a very quick way to get some idea about the area. You'll probably be anywhere between 0.5m to 10m accurate.
If you take GPS control points and you can recognize those points in the final photo, you can use that information to better "undistort" the model (meaning, it develops better estimates of the camera parameters like radial distortion and the focal length). The other issue is that it is a much more precise method for geo-referencing the result.
the precision of that method defines the absolute precision of the final model and it's possible to get this down to 5-10cm. But the equipment to achieve that is expensive.
Thanks for the complete anwser. For a budget between 200/300$, which camera is your favorite choice?
The best cameras are those that are lighter than the others and have the best optics for their price range. At the moment the Canon SX230HS, SX260HS, S100 are popular. If you go up in price a bit you get different options and slightly better optics.