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?
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?
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
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
https://opengeospatial.github.io/ogc-geosparql/geosparql13/document.html#13-9-24-%C2%A0-function-geof-metriclength
https://opengeospatial.github.io/ogc-geosparql/geosparql13/document.html#13-9-25-%C2%A0-function-geof-length
metricPerimeter, move the substantive part of the definition frommetricLengthtolength. This way you avoid any discrepancies between the definitions oflengthandmetricLength