Photoscan: Studying New Model Reconstruction Method
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Photoscan: Studying New Model Reconstruction Method
12 August, 2018
News
Tutorial

Agisoft has recently shared a tutorial that focuses on Photoscan’s new reconstruction method, which allows users to control thin structures like butterfly wings. It also shows how you can get better results with new strict volumetric masking feature.

New model reconstruction method

In previous versions of the software, polygonal model reconstruction required dense cloud data, and in some cases user faced the necessity to manually remove noise from the dense cloud, or to mask nearly all images before building dense cloud. New mesh reconstruction method uses depth maps directly without the need to generate dense point cloud first.

This article uses butterfly dataset as an example, the data having been kindly provided by Philadelphia Insectarium and Butterfly Pavilion in collaboration with MACROSCOPIC SOLUTIONS, LLC.:

To build model with the new method you should enable the functionality in PhotoScan 1.4 with Tools -> Preferences… -> Advanced -> Use visibility consistent mesh generation method. And then run Workflow -> Build Mesh… The only parameter that you need to choose is the quality of the depth maps used for mesh building. A mesh built from medium quality depth maps is illustrated below:

One can see that although the whole butterfly was reconstructed successfully, but too much of the textureless white background stuck to butterfly borders.

Strict volumetric masking

New model reconstruction method with strict volumetric masking makes it possible to remove this noise with a single mask. Please note that this masking is strict: each masked out pixel says to the algorithm that the ray coming from the respective camera through this pixel must pass only through the empty space. So please be careful and don’t mask something important.

Previously to prevent sticking textureless background to model it was required to create masks for all images (at least coarse masks with magic wand or by color). Now you don’t need to create so many masks: just reconstruct model without masks, and if there will be noisy volume, suppress it with strict volumetric mask on the image that observes the respective part of the space. Too many masks can lead to slow model reconstruction in case of strict volumetric masking.

White background can be masked out with magic wand:

The pillar below the butterfly wasn’t masked, because it is a little bit darker in color. You can complete the mask with scissors tool. Note that while you are holding Ctrl scissors path will automatically go along the texture border, and thus you will have to do just a few mouse clicks to perform the task

Note that to finish selection with scissors, you can just press Esc, and the current selection path will automatically be connected with the beginning (you can click Esc one more time to remove selection).

Be careful with all the meaningful parts: if you mask out a butterfly leg, it will not be reconstructed.

After masking out both left and right parts of the pillar with scissors, the mask will look like the following:

Now model can be built, with strict volumetric masking input being considered: Workflow -> Build Mesh… and tick Advanced -> Use strict volumetric masks.

Resulting model looks fine thanks to a single mask we applied:

Agisoft 

Make sure to study the full tutorial here

Source: agisoft.com

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