Functions: Output Subtype

[VladimirAlexiev]

I have some doubts about B.1. Functions Summary Table column Output Subtype (eg https://opengeospatial.github.io/ogc-geosparql/geosparql13/document.html#_328b184f-25e6-4b64-a46e-1e84e1e75574):

• aggBoundingBox -> square Polygon: guess you mean "rectangular"?
• Is Polygon appropriate for functions that return circles/arcs? I'm not sure whether GeoSPARQL incorporates geometries that can express circles/arcs, but: https://en.wikipedia.org/wiki/Well-known_text_representation_of_geometry says that WKB includes geometries like Circle, CircularString. It refers to https://github.com/cleder/parsewkt/blob/master/parsewkt/Wkt.ebnf , which includes CIRCULARSTRING but not CIRCLE.
  • aggBoundingCircle -> Polygon
  • buffer -> (Multi)Polygon
• Is Polygon appropriate for functions that may take simpler geometries as arguments? Eg the union of several Points should be MultiPoint and the union of several LineStrings should be MultiLineString, right? Even if the subtype is correct, the use of Polygon/(Multi)Polygon should be precised. Surely aggUnion can be a MultiPolygon?
  • aggUnion -> Polygon
  • difference -> (Multi)Polygon
  • intersection -> Polygon
  • symDifference -> (Multi)Polygon
  • union -> Polygon
• envelope -> (Multi)Polygon : should be Polygon since the function returns a rectangle (bounding box)

[situx]

I will try to answer your questions here, others of the group, e.g. @nicholascar may weigh in:

• aggBoundingBox: Yes the result will be rectangular, but the type e.g. in WKT but also in GeoJSON and other formats will be a Polygon, with 4 points, i.e. a rectangle, but typed a Polygon
• Is Polygon appropriate for functions that return circles/arcs?: The type of the output, of course, varies with what the literal format supports. In the case of WKT/WKB you could use a circle/arc datatype, but for most other formats you would need to approximate the circle with a Polygon. Nonetheless we could add the circle/datatype to the table for the literals that support it
• Is Polygon appropriate for functions that may take simpler geometries as arguments?: This is a good point. We may consider adding more types like this to the table.
• envelope: We will correct that one

[VladimirAlexiev]

@situx first bullet:

• still says "square Polygon", should be "rectangular Polygon"