geo structs about geo

[sunng87]

Perhaps we can follow some open standard like OGC Simple Feature Access

To answer some questions above (Just my opinion)

1. Base types: Point, LineString, Polygon; there are also some other types as defined in SFA 6.1 Geometry Object Model
2. Hole in polygon is represented as InteriorRing (A LineString). A polygon has only one exterorRing and 0 or multiple interiorRing. So wind order doesn't matter.
3. Self intersecting polygons are not supported (? you may check the definition in that document to confirm)
4. We don't need to deal with topology in this lib
5. (x,y) is required and z, m is optional
6. GeometryCollection is in this spec
7. Projections are out of this library's scope, only numeric coordinates are involved

[calvinmetcalf]

not a bad idea, the way point xy is distinct from point xyz fits well with rust fyi ogc has the same types as geojson (Point,LineString,Polygon,MultiPoint,MultiLineString,MultiPolygon,GeometryCollection) plus a few more (MultiCurve, MultiSurface,Curve, Surface, PolyhedralSurface, TIN).

The GeoJSON and some databases like postgres have a somewhat laxer view on self intersections and what not, then tends to be a bit more practical in the real world.

The OGC spec is awful, the page number are romen numerals for gods sack.

Hemisphere spanning polygons are still a problem

[sunng87]

SFA GOM is based on a classic object-oriented model, but in rust we prefer composition over inheritance, so we don't need to implement types like Curve, Surface...

I think the shared types of SFA and GeoJSON are in highest priority.

Another reference is JTS geom types. JTS is widely used in Java GIS libraries as foundation. You can find its type system is very practical.

[frewsxcv]

Maybe we should open separate GitHub issues to discuss each of these points individually to facilitate better, more organized discussion.

In terms of XYZM, does the M coordinate value ever get used for geospatial calculations like distance and area? After reading this I would think that it wouldn't.

[calvinmetcalf]

yeah m is rarely used, wkb specifically is pretty down to earth and is something we could translate into rust pretty easily

[frewsxcv]

Unless I'm looking at this incorrectly, it looks like JTS's distance operation only works on XY even though they offer XYZ (and M).

[sunng87]

True, seems the whole library doesn't use z for distance: https://github.com/simplegeo/jts/blob/master/src/com/vividsolutions/jts/algorithm/CGAlgorithms.java