Offset trait testing improvements

geo/src/algorithm/offset/line_intersection.rs

@@ -8,6 +8,8 @@ pub(super) enum FalseIntersectionPointType {
     /// ray defined by the line segment, but before the start of the line segment.
     ///
     /// Abbreviated to `NFIP` in original paper (Negative)
+    /// (also referred to as `FFIP` in Figure 6, but i think this is an 
+    ///  error?)
     BeforeStart,
     /// The intersection point is 'false' or 'virtual': it lies on the infinite
     /// ray defined by the line segment, but after the end of the line segment.
@@ -172,6 +174,8 @@ where
     }
 }
 
+/// Return the intersection point as well as the relationship between the point
+/// and each of the input line segments. See [LineSegmentIntersectionType]
 pub(super) fn line_segment_intersection_with_relationships<T>(
     a: &Coord<T>,
     b: &Coord<T>,

geo/src/algorithm/offset/offset_trait.rs

@@ -1,4 +1,7 @@
-use super::line_intersection::FalseIntersectionPointType::AfterEnd;
+use super::line_intersection::FalseIntersectionPointType::{
+    BeforeStart,
+    AfterEnd,
+};
 use super::line_intersection::LineSegmentIntersectionType::{
     FalseIntersectionPoint, TrueIntersectionPoint,
 };
@@ -51,7 +54,9 @@ where
     /// negative.
     ///
     /// Negative `distance` values will offset the edges of the geometry to the
-    /// left, when facing the direction of increasing coordinate index.
+    /// left, when facing the direction of increasing coordinate index. For a
+    /// polygon with clockwise winding order, a positive 'offset' corresponds with
+    /// an 'inset'.
     ///
     /// ```
     /// #use crate::{line_string, Coord};
@@ -86,6 +91,13 @@ where
     }
 }
 
+
+/// # Offset for LineString
+/// ## Algorithm
+/// Loosely follows the algorithm described by
+/// [Xu-Zheng Liu, Jun-Hai Yong, Guo-Qin Zheng, Jia-Guang Sun. An offset algorithm for polyline curves. Computers in Industry, Elsevier, 2007, 15p. inria-00518005]
+/// (https://hal.inria.fr/inria-00518005/document)
+/// This was the first google result for 'line offset algorithm'
 impl<T> Offset<T> for LineString<T>
 where
     T: CoordFloat,
@@ -102,6 +114,7 @@ where
         if offset_segments.len() == 1 {
             return offset_segments[0].into();
         }
+        // First and last will always work:
         let first_point = offset_segments.first().unwrap().start;
         let last_point = offset_segments.last().unwrap().end;
 
@@ -127,13 +140,23 @@ where
                             //println!("CASE 1 - extend");
                             vec![intersection]
                         },
-                        (FalseIntersectionPoint(AfterEnd), FalseIntersectionPoint(_)) => {
+
+                        (TrueIntersectionPoint, FalseIntersectionPoint(_)) => {
+                            //println!("CASE 1 - extend");
+                            vec![intersection]
+                        },
+                        (FalseIntersectionPoint(_), TrueIntersectionPoint) => {
+                            //println!("CASE 1 - extend");
+                            vec![intersection]
+                        },
+                        (FalseIntersectionPoint(BeforeStart), FalseIntersectionPoint(_)) => {
                             // TODO: Mitre limit logic goes here
                             //println!("CASE 2 - extend");
                             vec![intersection]
-                        }
+                        },
                         _ => {
-                            println!("CASE 3 - bridge");
+                            //println!("CASE 3 - bridge");
+                            //vec![intersection]
                             vec![*b, *c]
                         },
 

rfcs/2022-11-11-offset.md

@@ -23,7 +23,7 @@ Priority for implementing the trait is as follows:
 - [ ] If some of the limitations discussed below can be addressed
   - [ ] `Polygon`
   - [ ] `MultiPolygon`
-  - [ ] `Geometry` & `GeometryCollection`
+  - [ ] `Geometry` & `GeometryCollection
 
 ## Limitations
 
@@ -44,11 +44,11 @@ and potentially a better algorithm is needed:
 
 ### References
 
-Loosely follows the algorithim described by
+Loosely follows the algorithm described by
 [Xu-Zheng Liu, Jun-Hai Yong, Guo-Qin Zheng, Jia-Guang Sun. An offset algorithm for polyline curves. Computers in Industry, Elsevier, 2007, 15p. inria-00518005](https://hal.inria.fr/inria-00518005/document)
 This was the first google result for 'line offset algorithm'
 
-### Definitions (For the psudocode in this readme only)
+### Definitions (For the psudo-code in this readme only)
 
 Type definitions
 ```python