Eliminate the possibility of the perspective transform collapsing #1489
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Prior to this change, while the perspective transform could collapse at any selection of the scale parameter, it was especially more prevelant for higher values of scale. Specifically, the randomly generated transformation polygon had a non-zero chance of concave, which led to collapsed perspective transformations. A more refined (and easier to understand) solution requires the implementation of "Concave Polygon Recoverer" like in imgaug. However, restricting the randomly generated `points` values [0, 1/3] ensures geometrically that the generated polygon will be convex, hence resulting in a valid (uncollapsed) perspective transformation. The upper limit is set to 0.32 instead of 1/3, to avoid any potential numerical issues (due to near-concave polygons), with the same motivation behind the piece of code ensuring that `min_height` and `max_height` are over 2.0, shortly following the polygon generation.
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Prior to this change, while the perspective transform could collapse at any selection of the
scaleparameter, it was especially more prevelant for higher values ofscale. Specifically, the randomly generated transformation polygon had a non-zero chance of being concave, which led to collapsed perspective transformations.A more refined (and easier to understand) solution requires the implementation of "Concave Polygon Recoverer" like in imgaug. That being said, simply restricting the randomly generated
pointsvalues to the range [0, 1/3] ensures geometrically that the generated polygon will be convex, hence resulting in a valid (uncollapsed) perspective transformation.In the code, I set the upper limit at 0.32 instead of 1/3, to avoid any potential numerical issues (due to near-concave polygons), with the same motivation behind the piece of code ensuring that
min_heightandmin_widthare over 2.0, shortly following the polygon generation.Fixes #1001