[DL-720] Polygon support

[farizrahman4u]

🚀 🚀 Pull Request

Checklist:

• [ ] My code follows the style guidelines of this project and the Contributing document
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have kept the coverage-rate up
• [ ] I have performed a self-review of my own code and resolved any problems
• [ ] I have checked to ensure there aren't any other open Pull Requests for the same change
• [ ] I have described and made corresponding changes to the relevant documentation
• [ ] New and existing unit tests pass locally with my changes

Changes

Adds support for polygon htype

Usage

ds.create_tensor("polygons", htype="polygon")

Default dtype is float32. Other dtypes can be specified:

ds.create_tensor("polygons", htype="polygon", dtype="int32")

• Each sample is a list of polygons. Each polygon is a list of points.
• All points in a sample should have same dimensions. (Can not mix 2D points with 3D points etc).
• Different samples can have different number of polygons.
• And different polygons can have different number of points.

poly1 = [(1, 2), (2, 3), (3, 4)]
poly2 = [(10, 12), (14, 19)]
poly3 = [(33, 32), (54, 67), (67, 43), (56, 98)]

sample = [poly1, poly2, poly3]

ds.polygons.append(sample)

Data Layout

• Each sample in the chunk has the following format: [Header][Data]

• The header looks like this: [num polygons (uint16)][list of lengths of each polygon (uint16)]

• The data is simply all the points as a flat buffer.

• The dtype and number of dimensions can be inferred from tensor meta (.dtype and .max_shape[-1] respectively). This information is NOT stored in chunks.

• Sample compression and chunk compression with lz4 are supported.

• NOTE: Whole buffer will be empty for empty samples. Even header will not be present.

[codecov[bot]]

Codecov Report

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[FayazRahman]

Also need to make hub.core.Polygons page visible on docs