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attempt to better document Simplify traits epsilon parameter #1151

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Feb 23, 2024
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attempt to better document Simplify traits epsilon parameter #1151

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attempt to better document Simplify traits `epsilon` parameter
michaelkirk Feb 20, 2024
186e9a7
fixup! attempt to better document Simplify traits `epsilon` parameter
michaelkirk Feb 20, 2024
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16 changes: 14 additions & 2 deletions geo/src/algorithm/simplify.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -153,7 +153,13 @@ where
///
/// Multi* objects are simplified by simplifying all their constituent geometries individually.
///
/// An epsilon less than or equal to zero will return an unaltered version of the geometry.
/// A larger `epsilon` means being more aggressive about removing points with less concern for
/// maintaining the existing shape.
///
/// Specifically, points closer than `epsilon` distance from the simplified output may be
/// discarded.
///
/// An `epsilon` less than or equal to zero will return an unaltered version of the geometry.
pub trait Simplify<T, Epsilon = T> {
/// Returns the simplified representation of a geometry, using the [Ramer–Douglas–Peucker](https://en.wikipedia.org/wiki/Ramer–Douglas–Peucker_algorithm) algorithm
///
Expand Down Expand Up @@ -192,7 +198,13 @@ pub trait Simplify<T, Epsilon = T> {
/// This operation uses the [Ramer–Douglas–Peucker algorithm](https://en.wikipedia.org/wiki/Ramer–Douglas–Peucker_algorithm)
/// and does not guarantee that the returned geometry is valid.
///
/// An epsilon less than or equal to zero will return an unaltered version of the geometry.
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A related question is can we alter our algorithm such that epsilon == 0 will remove collinear points, but nothing else?

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@michaelkirk michaelkirk Feb 20, 2024 •
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Maybe with distance and area calculations it's not feasible to have epsilon == 0 from a robustness perspective...

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Hmm I don't know that either algorithm can be made to work precisely like that. I can have a look at "the literature".

/// A larger `epsilon` means being more aggressive about removing points with less concern for
/// maintaining the existing shape.
///
/// Specifically, points closer than `epsilon` distance from the simplified output may be
/// discarded.
///
/// An `epsilon` less than or equal to zero will return an unaltered version of the geometry.
pub trait SimplifyIdx<T, Epsilon = T> {
/// Returns the simplified indices of a geometry, using the [Ramer–Douglas–Peucker](https://en.wikipedia.org/wiki/Ramer–Douglas–Peucker_algorithm) algorithm
///
Expand Down
14 changes: 12 additions & 2 deletions geo/src/algorithm/simplify_vw.rs
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Expand Up @@ -479,7 +479,12 @@ pub trait SimplifyVw<T, Epsilon = T> {
/// This operation uses the Visvalingam-Whyatt algorithm,
/// and does **not** guarantee that the returned geometry is valid.
///
/// An epsilon less than or equal to zero will return an unaltered version of the geometry.
/// A larger `epsilon` means being more aggressive about removing points with less concern for
/// maintaining the existing shape. Specifically, when you consider whether to remove a point, you
/// can draw a triangle consisting of the candidate point and the points before and after it.
/// If the area of this triangle is less than `epsilon`, we will remove the point.
///
/// An `epsilon` less than or equal to zero will return an unaltered version of the geometry.
pub trait SimplifyVwIdx<T, Epsilon = T> {
/// Returns the simplified representation of a geometry, using the [Visvalingam-Whyatt](http://www.tandfonline.com/doi/abs/10.1179/000870493786962263) algorithm
///
Expand Down Expand Up @@ -516,7 +521,12 @@ pub trait SimplifyVwIdx<T, Epsilon = T> {

/// Simplifies a geometry, attempting to preserve its topology by removing self-intersections
///
/// An epsilon less than or equal to zero will return an unaltered version of the geometry
/// A larger `epsilon` means being more aggressive about removing points with less concern for
/// maintaining the existing shape. Specifically, when you consider whether to remove a point, you
/// can draw a triangle consisting of the candidate point and the points before and after it.
/// If the area of this triangle is less than `epsilon`, we will remove the point.
///
/// An `epsilon` less than or equal to zero will return an unaltered version of the geometry.
pub trait SimplifyVwPreserve<T, Epsilon = T> {
/// Returns the simplified representation of a geometry, using a topology-preserving variant of the
/// [Visvalingam-Whyatt](http://www.tandfonline.com/doi/abs/10.1179/000870493786962263) algorithm.
Expand Down
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