Add contour line extraction via marching squares (#964)#974
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New xrspatial.contour module with contours() function that extracts isolines from 2D rasters. Supports numpy, cupy, dask+numpy, and dask+cupy backends. Includes segment stitching into polylines and optional GeoDataFrame output.
Corrected edge assignments in the marching squares lookup table. Previous table had wrong edges for most cases (e.g. case 1 used top edge instead of bottom edge). Added comprehensive test suite covering correctness, NaN handling, edge cases, backend equivalence, GeoDataFrame output, accessor integration, and closed-ring detection.
Matplotlib-based interactive app for exploring contour lines on procedural terrain. Supports click-to-add levels, scroll density control, filled contours, hillshade toggle, contour labels, index contours, and colour scheme cycling.
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Summary
contours()function for extracting isolines from 2D rasters using marching squares@ngjitkernel), Dask+NumPy (chunked viada.overlap), CuPy and Dask+CuPy (CPU fallback, same approach aspolygonize)polygonizeChanges
xrspatial/contour.py-- marching squares kernel, four backend functions, segment stitcher, publiccontours()APIxrspatial/tests/test_contour.py-- 22 tests: correctness, NaN handling, edge cases, backend equivalence, GeoDataFrame output, accessor integrationexamples/user_guide/22_Contour_Lines.ipynb-- user guide notebook with terrain generation, contour extraction, hillshade overlay__init__.py,accessor.py-- exports and.xrs.contours()accessordocs/source/reference/utilities.rst-- API docs entryREADME.md-- feature matrix rowTest plan
pytest xrspatial/tests/test_contour.py-- 21 passed, 1 skipped (skimage reference test, skimage not installed)Closes #964