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Jack Hubler-Dayton

Problems with Flat Runs on Pottery

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Hi All!

Longtime lurker here, I AM having trouble getting Photoscan (regular licence) to recognize both sides of a pottery fragment. I am getting a lot of holes on the sides and the bottom isn't being built. Unfortunately I don't scale bars which I know would help. I attended the Sept 2016 photogrammetry training with CHI in San Francisco. Since graduating college in 2017 I have continued to model but mostly on objects in the round or completely flat and immovable like petroglyphs. I know I need different camera calibration sets and blank shots for building the masks. Any help would be appreciated. 

 

Jack 

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If I understand correctly, your objects are flatter (as in plates).  In this case the main problems are linking images between the top and bottom of the object. This usually requires more images with more overlap as the camera approaches the edge. Depth of field can also be a problem if similar views from top and bottom image sets don't have matching areas that are completely in focus.

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Ozbigben,

I am aware of the issue getting good tie points on the edges of more 2d subjects. Do you have any tips for getting more good look angles on the edges, or getting more of the whole sherd in focus?  I know that the recommended f stop should be no higher than f11 from CHI. I have exceeded that limit occasionally after talking with Charles Walbridge from the MIA who is active on this forum. I have been shooting on a clean background and then flipping the object and getting a few circuits  on either side, I'll post some screen caps in a bit. 

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Jack -

It would help to see some screen shots of what is happening.  Things with narrow edges are difficult to get alignment of the 2 sides.  I can't tell from your post, whether you are shooting circuits with the pieces upright, or shooting each side and turning over. That would affect the approach to solving this.  Also since you say that images of the "bottom" don't align - I'm wondering if they would align to themselves in a separate chunk - then you might be able to bring the chunks together. That is not the optimum way to do it, but it could be a interesting test.  I think you know that the biggest issue with relatively flat subjects, is having enough data across the thin edges to get the sides to be in the right relationship to each other.  Also, if you shoot each side, you can put each side on a different background, so that the software doesn't match the backgrounds - this can create errors in alignment.  That kind of problem could be solved by masking - but it's easier to just use different backgrounds.  

Carla

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