## Friday, May 6, 2016

### Multi View stereo - Gilbert pink granite stone

Let's see the effect of the max reprojection error (low-confidence image points) on the 3D reconstruction produced by Multi View Stereo 10 (MVS10). If the reprojection error of an image point is too large, it is assumed the image point is not reliable and if the number of image points goes below the minimum number of image points, then it is the 3D point itself that's considered unreliable.

Let's start with max reprojection error (low-confidence image points) = 2. Incidentally, we are using min separation angle (low-confidence 3D points) = 0.5 and min image point number (low-confidence 3D points) = 3. Those are fixed.

MVS10 outputs:
Number of 3D points = 1,300,510
Number of 3D points removed because behind ref camera = 23,295
Number of 3D points removed because separation angle too low = 270,093
Number of 3D points removed because too few image points = 635,181
Number of 3D points = 371,941

Let's continue with max reprojection error (low-confidence image points) = 4 and see what happens to the 3D reconstruction.

MVS10 outputs:
Number of 3D points = 1,220,135
Number of 3D points removed because behind ref camera = 22,258
Number of 3D points removed because separation angle too low = 206,778
Number of 3D points removed because too few image points = 412,677
Number of 3D points = 578,422

As expected, when the max reprojection error (low-confidence image points) is raised, the final number of 3D points in the 3D reconstruction increases. Are those extra 3D points erroneous? They don't appear to be, at least when the 3D reconstructions are viewed in animated gif form.