Photogrammetry has incredible potential in archaeological research and education. However, despite Agisoft PhotoScan’s relatively simple initial workflow, things get complicated pretty quickly. Those of us using the program tend to learn by solving problems as they occur, but this is a very piecemeal, time-consuming, and often frustrating process. Currently, anyone getting started with the program must either go through the same thing, or find someone to offer guidance.
In this series I will assemble all the separate tips that I have learned or found into a step-by-step guide on the basic process (posted weekly). I do not consider myself an expert in PhotoScan. If you are familiar with the program and have any corrections or additions, please let me know.Each week, the previous step will be edited to include any comments and placed under the “Resources” menu to serve as a guide for beginners.
The previous steps can be found here.
Step 6: Building the Mesh
You have created your dense point cloud and it is time to turn all of those points into a “solid” object. Before proceeding though, check your dense cloud for any errors and remove them the same way you did with the sparse cloud. I always have some cleaning up to do, but not nearly as much since I started doing the “Gradual Selection” process in Step 4.
Jeremiah Stager points out that you can further clean up the dense cloud by going to Tools> Dense Cloud> Select Points by Color. He recommends starting with white or black and increasing the tolerance to remove points that are errors in the model.
Now, go to your “Workflow” drop-down menu again and select “Build Mesh…” and the relevant window will pop up with new options.
- “Surface Type” should be left at “Arbitrary” unless you are modeling from aerial photography.
- “Source Data” should be your dense cloud. If the menu says “Sparse cloud” switch it.
- “Face Count” puts a limit on how many triangles PhotoScan will apply. When we turn these points into a solid object, the resulting model is made up of lots of little triangles. Each triangle is a face. When making a model to share on Sketchfab 500,000 faces is a good upper limit. I have had good luck with up to 1 million faces, though this is close to what my computer can comfortably handle (once I apply a texture in Step 7). If you put “0” in this box you are placing no limit on the number of faces. Be careful with this, I have accidently created models with over 22 million faces this way. This made my computer cry.
Under the “Advanced” tab:
- “Interpolation” describes how much the program automatically fills in holes. “Enabled (default)” is the middle ground where small holes are filled in. If you need perfect accuracy and do not mind holes you can select “Disabled” otherwise “Extrapolated” makes sure there are no holes left.
- “Point Classes” I think are related to more aerial photographs. Here is a tutorial on creating them if you need it, otherwise ignore this option.
Click “OK” when you are satisfied. The progress window will pop up again. This may take up to an hour.