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Author Topic: small size of GCP printed markers - for small models 10 to 50cm  (Read 2240 times)

hilary

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small size of GCP printed markers - for small models 10 to 50cm
« on: December 02, 2016, 09:57:24 AM »
Hello,

I am working on an interesting project where I need to make 3D models of the carved fronts of individual stone blocks ... and blocks are stacked up in a big pile and can not be moved.

The blocks that are stacked in the pile do not line up perfectly; all of the decorated front faces are on a slightly different plane. The 3D models I make of the faces need to be co-planar, they need to be looked at straight-on.

I have been printing small auto-detected 12 bit gcp targets I stick three targets on the front face of each block, and then an orthomosaic is built on the projection plane created on the plane of the three markers. Some of the block faces are quite small and therefore I need SMALL targets. Sometimes I can get 2cm 12 bit targets recognized and auto-detected, which saves time, and sometimes they are not seen at all.

Due to the scope of the project, there isn't time to put in every marker manually. 

Does anyone have any information or tips on how to get gcp targets recognized that are very small? So much of the forum talks about targets that are large, for aerial surveys.

Are other people making models that are small.. on average 10 - 50cm wide? I have tested out crosses and 'x' shapes, and they do not get auto-recognized. Can the inner white circle be made larger on the gcp's... or there any tricks to boost recognition? (I have tried adjusting the relevance slider).

thanks!
 

Kiesel

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Re: small size of GCP printed markers - for small models 10 to 50cm
« Reply #1 on: December 02, 2016, 05:57:10 PM »
Hello Hilary,

Coded targets are for close range photogrammetry, so you are absolutly right to use them for your project. They are often to big than to small (for arial photogrammetry they are often to small and you can't use them). In the following tutorial by Agisoft it is stated that ".. the size of central black circle-point on the taken photo is not bigger than 30 pix." in diameter in your photo.

For the tutorial see here: http://www.agisoft.com/pdf/PS_1.1_Tutorial%20(IL)%20-%20Coded%20Targes%20and%20Scale%20Bars.pdf

God luck with your project,

Karsten