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What units
are allowed for geof:distance, geof:buffer
?
#468
Comments
I think we deliberately did not constrain the unit parameter to a specific vocabulary, and the uom:metre example was, at the time of definition of GeoSPARQL 1.0, probably the only vocabulary around or recommended by OGC. We did not define default values for the geof:buffer function per se, but you could consider the metric versions e.g. metricBuffer as default functions |
But shouldn't the spec at least say: these should be Length units, |
We do have section 8.3, which recommends vocabularies for Units of Measure for all GeoSPARQL functions. Yes, we could have written that we would recommend a length unit for clarity in the case of geof:buffer |
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Does that mean it's ok to use
|
Yes, you would be free to use these other units like degree. Whether it makes sense to use them in your context is one question. Whether the implementation is willing to support it and how is another one we did not aim to solve in the specification as to not restrict the standard unnecessarily. We do not even mandate that all or any of the uom units should be supported. If we were to restrict the unit to uom:metre only, then our function would be useless because there is still geof:metricBuffer which is restricted to meter already. But I think I know what you mean: We should probably provide some useful examples concerning different units and how people might typically want to use them in practice in order to make the choice for supporting units easier for implementers. |
when more and more geometry formats are supported with GeoSPARQL 1.2+, so will increase the number of "input" units for spatial functions. Units are defined in a CRS and/or in the geometry description itself. Sometimes, there are clear and standard IDs/URIs for units, but in some frequently used geometry formats such as STEP in IFC, these are "just" strings which have to be harmonized still by an interpreter before executing a spatial function. When many different kinds of input units becomes a reality, I think this increases the need for a clear and harmonized approach to units in the "output" of spatial functions. For what it's worth, the construction industry in Europe already agrees on using QUDT for quantitative properties (e.g. "volume" which is calculated from a 3D geometry description) by the EN 17632-1. It's already applied in several companies as we speak. |
@situx Please give your personal opinion: does this guess make sense:
@mathib I'm very interested in applications of GeoSPARQL to architectural geometry. I've seen some 3D functions in GeoSPARQL (eg
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#398 suggests that Therefore this guess
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What units are allowed for the functions
geof:distance, geof:buffer
?GeoSPARQL 1.0 defines them merely as
units: xsd:anyURI
, eg:Our own documentation https://graphdb.ontotext.com/documentation/10.5/geosparql-support.html#example-4
shows an example from the
uom: <http://www.opengis.net/def/uom/OGC/1.0/>
namespace.One can explore that namespace eg at
And the members of that collection are:
Of these, only
metre
seems a suitable value?uom:GridSpacing
begs the question: which grid?degree
andradian
could be interpreted as "angular measure at the equator (111139 m and 6367798 m respectively)?Is there are default value, i.e. is it ok to leave
units
unbound?Links:
units
is unboundThe text was updated successfully, but these errors were encountered: