clarify geof:length vs geof:perimeter

[VladimirAlexiev]

I find the descriptions of length and perimeter, and the difference between them, unclear:

https://opengeospatial.github.io/ogc-geosparql/geosparql13/document.html#13-9-33-%C2%A0-function-geof-perimeter

geof:perimeter returns the perimeter of geom in the unit specified by the unit parameter for areal geometries. For non-areal geometries the result is equivalent to geof:hasLength.

• geof:hasLength should be geof:length
• since geof:length is also applicable to areal features ("length of the boundary of a polygon"), what is the difference?
• if the polygon has holes, are they added to the perimeter?

https://opengeospatial.github.io/ogc-geosparql/geosparql13/document.html#13-9-24-%C2%A0-function-geof-metriclength

The function geof:metricLength returns the length of geom in meters. The longest length from any one dimension is returned. This is for example the length of a line from its beginning point to its endpoint or the length of the boundary of a polygon. This function is similar to geof:length but does not need a specification of measurement unit.

• "longest length from any one dimension" sounds like the diameter of a feature. What's the purpose of this sentence? I think delete it
• "length of the boundary of a polygon": this is the textbook definition of "perimeter", isn't it?

https://opengeospatial.github.io/ogc-geosparql/geosparql13/document.html#13-9-25-%C2%A0-function-geof-length

The function geof:length returns the length of geom. The longest length from any one dimension is returned. This function is similar to geof:metricLength, which does not need a specification of measurement unit.

• Following the example of metricPerimeter, move the substantive part of the definition from metricLength to length. This way you avoid any discrepancies between the definitions of length and metricLength