About the Spatial Meronymy and Spatial Operators requirements (help needed!)

All,

I am in need of assistance for formulating requirements in the UCR document.

This call for help is triggered by a remark from Bill Roberts in the UCR
spreadsheet
<https://docs.google.com/spreadsheets/d/1PSnpJYQDgsdgZgPJEfUU0EhVfgFFYGc1WL4xUX9Dunk/edit?usp=sharing>.
The remark added to the Spatial Meronymy requirement
<http://w3c.github.io/sdw/UseCases/SDWUseCasesAndRequirements.html#SpatialMeronymy>
reads:

*"This standard should include not only whether A contains B, but to
express that A can be broken down into B,C,D which exactly cover A and do
not overlap.*

*Also, that there can be several different collections of sub-areas that
make up a parent area. [..]**"*

My initial thought was that that this further specification could be
covered by the Spatial Operators requirement
<http://w3c.github.io/sdw/UseCases/SDWUseCasesAndRequirements.html#SpatialOperators>.
And then I started wondering why there are two different requirements at
all. Then I started to try to find some information on the web about
spatial meronymy and possible relationships with topological relationships.
Then I started to become overwhelmed. Well, at least I think I found out it
is probably better to speak of  'spatial mereology'  than 'spatial
meronymy'.

One aspect I wondered about is computability. I think that the topological
relationships that are in use in by the OGC as described by the DE-9IM
<http://en.wikipedia.org/wiki/DE-9IM> model are computable, i.e. one needs
quantitative geometries to determine a topological relationship. Can anyone
confirm or deny that? For example, let's say that there are two spatial
objects that have no clear boundaries, like the Sahara desert and the
Tanezrouft <http://en.wikipedia.org/wiki/Tanezrouft>. From a mereology
perspective, we could say 'The Tanezrouft is part of the Sahara'. Could we
also make a similar statement from the DE-9IM perspective, e.g. 'The Sahara
contains the Tanezrouft', if there is no way to compute whether the
statement is true or false?

Another thing to consider is the difference between spatial functions and
spatial properties. A spatial property can describe a relationship (e.g.
'object A  overlaps  object B'). A spatial function can determine a
relationship (e.g. 'return all objects that overlap  object A'). There is a
need for both and a standard like GeoSPARQL has separated the two, e.g. geo:
sfContains is a property and geof:sfContains is a function (note the
different name space prefix). With the requirements phrased as they are now
the need for standardised spatial properties does not seem covered.

I am now leaning towards suggesting changing the Spatial Meronymy
requirement
<http://w3c.github.io/sdw/UseCases/SDWUseCasesAndRequirements.html#SpatialMeronymy>
to
a more general Spatial Relationships requirement:

1) There should be a standardised way for expressing spatial relationships
between spatial entities. These relationships can be topological,
mereological, directional or distance related.

The Spatial Operators requirement
<http://w3c.github.io/sdw/UseCases/SDWUseCasesAndRequirements.html#SpatialOperators>
perhaps
needs no change, but we could consider specifying that we understand
functions or operators to work on numerical data (so that includes raster
data next to vector data)

2) There should be standards for functions or operators working with
numerical spatial data.

Rightly phrased requirements are what is needed most at the moment, I hope
we can agree on them.

Regards,
Frans


-- 
Frans Knibbe
Geodan
President Kennedylaan 1
1079 MB Amsterdam (NL)

T +31 (0)20 - 5711 347
E frans.knibbe@geodan.nl
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