update CHANGELOG

CHANGELOG.md

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 ## 0.41.0
 
+Improve polygon algorithms.
+
 #### Features
 
-- Rewrite the `polygon` module to depend on `opencv` instead of `scikit-image` for finding contours. This change improves the algorithm runtime and fixes some previous unstable behavior in finding nested contours. For an introduction to the methodlogy, see the [OpenCV contour tutorial](https://docs.opencv.org/master/d4/d73/tutorial_py_contours_begin.html).
+- Rewrite the `polygon` module to run computation with [opencv](https://docs.opencv.org/4.x/index.html) in place of [scikit-image](https://scikit-image.org/) for finding contours. This change improves the algorithm runtime and fixes some previous unstable behavior in finding nested contours. For an introduction to the methodology, see the [OpenCV contour tutorial](https://docs.opencv.org/master/d4/d73/tutorial_py_contours_begin.html).
 
 #### Breaking changes
 
-- Completely rewrite the `polygon` module. Replace the "main" public function `polygon.find_contours_to_depth` with `polygon.find_multipolygon`. Return `shapely` objects when convenient to do so. Replace the `polygon.contour_to_lat_lon` function with `polygon.multipolygon_to_geojson`.
-- Remove parameters `min_area_to_iterate` and `depth` in the `MetDataArray.to_polygon_feature` method. The `depth` parameter has been replaced by the boolean `interiors` parameter. Add a `properties` parameter for adding properties to the `Polygon` and `MultiPolygon` features.
+- Completely rewrite the `polygon` module. Replace the "main" public function `polygon.find_contours_to_depth` with `polygon.find_multipolygon`. Replace the `polygon.contour_to_lat_lon` function with `polygon.multipolygon_to_geojson`. Return `shapely` objects when convenient to do so.
+- Convert continuous data to binary for polygon computation.
+- Remove parameters `min_area_to_iterate` and `depth` in the `MetDataArray.to_polygon_feature` method. The `depth` parameter has been replaced by the boolean `interiors` parameter. Add a `properties` parameter for adding properties to the `Polygon` and `MultiPolygon` features. The `max_area` and `epsilon` parameters are now expressed in terms of latitude-longitude degrees.
+
+#### Internals
+
+- Add `opencv-python-headless>=4.5` as an optional "vis" dependency. Some flavor of `opencv` is required for the updated polygon algorithms.
 
 ## v0.40.1