Since i recently learned those better refinement tricks for applying photogrammetry I've obtained a renewed interest in doing photogrammetry. I found myself digging through old datasets that I had attempted to use for photogrammetry that I was generally unsuccessful with. I always thought it was because i was taking bad photogrammetry photos, but given what i know now, it's likely because i didn't do enough post-processing work to help agisoft focus on the right features by using photomasks, and manually cleaning up the dense mesh.
After playing a few days with more data sets, i've learned that how and where you do a photomask is critical to getting all the cameras aligned. Take this example:
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| Before |
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| After |
You can see that before I had cropped out just the tank - this has pros and cons - by masking it everything outside the mask will not be computed for establishing tie points or the dense cloud because they are masked out of the region of interest. The problem with this is that i was unable to align all my photos (failed to compute where the cameras were) because there were not enough features in the image to align them all. The After image solves this because the newspaper which is feature rich (the faces, corners, blocks of text) makes a great element that can be clearly seen in multiple images from different perspectives. So in this case, i tried again by by recropping the images to include the newspaper i can get all the images aligned and build a dense mesh. You can see from just my 28 images I was able to get a 'OK' dense cloud of which i can now delete the newspaper off.
The next problem i have to face is that the tank treads were really dark and agisoft couldn't localize the voxels in these regions likely due to difficulty in matching these features between subsequent pictures. I guess I could've taken more pictures, or tried to get flatter lighting to combat this. Obviously, I have more practice and learning to do.
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