Implement Simplification traits for more things #135
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I was tempted to implement the simplification for But I didn't do it this time, I'm in two minds about whether it sensible. |
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We should note that in the case of Polygons and MultiPolygons, the simplification operation is not guaranteed to return a valid geometry (and we're back to validity!). A well-performing fix is dependent upon a usable R* implementation (I have a look occasionally, but results have been mixed). |
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(I've had a look at the JTS topology-preserving implementation – I don't do much Java, but it looks to be the naïve version described above. I'm not sure about GEOS, but I assume it's the same) |
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I have expanded the comments w.r.t. validity and topology |
src/algorithm/simplify.rs
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| @@ -52,7 +52,7 @@ fn rdp<T>(points: &[Point<T>], epsilon: &T) -> Vec<Point<T>> | |||
| /// The [Ramer–Douglas–Peucker | |||
| /// algorithm](https://en.wikipedia.org/wiki/Ramer–Douglas–Peucker_algorithm) simplifes a | |||
| /// linestring. Polygons are simplified by running the RDP algorithm on all their constituant | |||
| /// rings. | |||
| /// rings. This may result in invalid Polygons, and has no guarantee of perserving topology. | |||
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Should be "constituent" and "preserving".
src/algorithm/simplifyvw.rs
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| /// are simplified by simplifing all their constituant geometries individually. | ||
| /// Polygons are simplified by running the algorithm on all their constituant rings. This may | ||
| /// result in invalid Polygons, and has no guarantee of perserving topology. Multi* objects are | ||
| /// simplified by simplifing all their constituant geometries individually. |
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Should be "simplifying" and "constituent".
If you can simplify LineStrings, it makes sense that you can simplify a collection of linestrings (i.e. a multilinestring).
It simplifies their constituent linestrings.
Just simplify their constituent Polygons
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I have rebased & fixed up those typo fixes now. |
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Thanks for making the changes. PR looks good to me. 👍 |
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this is great, thanks! opened a new issue for reminding us about this potentially creating invalid geometries (#142) bors r+ |
135: Implement Simplification traits for more things r=frewsxcv If you can simplify a `LineString`, then you can simplify a `MultiLineString`. I also added implementations for the simplification traits for`Polygon` (and `MultiPolygon`), which just perform the simplification on the constituant linestrings that make up polygon. PostGIS's `ST_Simplfiy` does this AFAIK. The link for VM algorithm shows a polygon (the USA) being simplified, so the concept of "simplifying a polygon" is well understood.
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If you can simplify a
LineString, then you can simplify aMultiLineString.I also added implementations for the simplification traits for
Polygon(andMultiPolygon), which just perform the simplification on the constituant linestrings that make up polygon. PostGIS'sST_Simplfiydoes this AFAIK. The link for VM algorithm shows a polygon (the USA) being simplified, so the concept of "simplifying a polygon" is well understood.