Need help placing markers in Agisoft Photoscan

Hello,

I'm new to Agisoft Photoscan and am trying to use it for the first time.  I'm using Pixhawk on a hexacopter with a nex5 camera to get aerial images. I am able to georeference the pictures using mission planner. The camera is triggered by pixhawk every 15 meters. I fly a sloppy grid pattern over a friends house the other day for practice, and created my first aerial photo stitch in Agisoft Photoscan using 37 photos.

Here is the stitch I made.

3691104458?profile=original

 I am able to align camera positions and create a nice stitch, but I want to be able to produce more accurate results.

I'm following this guide here, and I get stuck when placing markers. 

I have markers placed, and aligned on all photos.

3691104338?profile=original

Where I get lost, is when the guide talks about inputting marker coordinates. I'm sure this is simple, but I can't seem to find anything on it, everything I read assumes you know how to do this. How do I get the real world coordinates of where my markers are on my photos?

3691104483?profile=original

I would appreciate anyone's help on using these markers to improve accuracy, sorry if this is a dumb question. 

Thanks,

Nick

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Replies

  • Another tip...

    These points are used to remove distortion resulting from algorithms and inaccuracies in GPS during the flight. Your orthophoto is a lot larger than the points you have mapped out. To get rid of these distortion effects, 5 control points are a minimum. You should place them in the 4 corners too on something you can easily identify and one in the middle.

    You can take additional control points that you do *not* feed into the algorithm on the edges for example, which you use to verify if the position that you eventually read out for that point in the software is about equal to what you measured there. These are verification points.

    • Thanks for your time to answer my question, Gerard. That explains it very well, very informative. 

  • Hi Nick,

    First of all, very nice results. congratulations!

    The coordinates are measured by a GPS as accurate as you can find. A smartphone is usable if you install an app that shows GPS coordinates (make sure you get an app that is precise enough, i.e. uses at least 6 decimals after the comma).

    In real life, you'd want a GPS more accurate than that, better than 10cm. There are GPS RTK handhelds that you can sometimes get for $3000 or so. Yes, that stuff is expensive. A piksi can also do this for you. Sometimes you need to leave the device there for some 30 minutes to allow the signals to settle, other devices use one static base station and one for running around so you can collect points faster.

    So the idea is just to use a device to get these coordinates from the real world and input them into long/lat/alt for the markers. With this method, you're closer or on the real points that are being reconstructed, so this allows any offsets that could have occurred due to camera misplacement and GPS errors there to be shifted back to reality.

    With a good GPS, you should expect <5cm horizontal accuracy that way. WIth iPhone, it's probably going to be around 1 meter.

    If you leave your iPhone at the same marker for a minute before doing the readout you'll probably get the best results.

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