like GeospatialGeometry but not partial, eg no empty geometries. Also can put an inveriant on dimensions if a function requires it. for example st_intersects PostgisGeometry PointXY can't work with PostgisGeometry PointXYZ. PointXY indicates a 2 dimension space, and PointXYZ a three dimension space.

Guarantees we don't accidently mix curved space with flat space. Postgis will catch this too, this just put's it in the type system.

unwrap postgis geometry so you can for example return it from an API

Returns TRUE if geometry A contains geometry B. https://postgis.net/docs/ST_Contains.html

Returns true if two geometries intersect. Geometries intersect if they have any point in common. https://postgis.net/docs/ST_Intersects.html

allows union of geometries, eg group a bunch together, https://postgis.net/docs/ST_Union.html for example:

 mCombined <- selectOne $ do
   grid <- from $ table Grid
   pure $ st_union $ grid ^. GridGeom


 select $  do
   unit <- from $ table Unit
   forM_ mCombined $ combined ->
     where_ $ (unit ^. UnitGeom) st_intersects (val $ unValue combined)
   pure unit

Returns true if the geometries are within a given distance https://postgis.net/docs/ST_DWithin.html

calculate the distance between two points https://postgis.net/docs/ST_Distance.html

Project a geography onto a geometry. allows using of functions such as st_union which only work in flat space (geometry). https://postgis.net/docs/ST_Transform.html

project a geometry as a geography, assumes wgs84. https://postgis.net/docs/ST_Transform.html

SRID you can find your local like this: https://blog.rustprooflabs.com/2020/11/postgis-find-local-srid geography appears to use wgs84. So I hardcoded the use going from geom to geography as that.

you can use the num instance to put in whatever. however, if you miss a srid please submit a PR.

default for geography type in postgis. Geodetic CRS: WGS 84 https://epsg.io/4326

most maps are in this, it has some large distortions further away from equator https://epsg.io/3857

if you're in england this is pretty good. https://epsg.io/27700

Diferent SRID come in different units, important for converting from geograhy to geometry.

checks if the first point is the last, and if not so makes it so. this is required for inserting into the database

backwards compatibility, initial version only dealt in geometry

technical typeclass to bind a spatial type to a string value. because we represent the constructors as a datakind, we need this to go back to a value.

(GeoPositionWithoutCRS is a catch all for indeterminate CRSs and for expression of positions before a CRS has been determined