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Subject: RE: Various examples of GML documents for Point, Polygin, and Circle
As promised, some examples of light weight GML encodings for point,
polygon, and circle. I am sure there are others! FYI, the IETF is using
GML 3.1 to define a point geometry for use in PIDF-LO. Their use cases are being
driven by emergency services requirements for expressing locations of IP address
location in buildings (using a DHCP location payload).
Anyway -
Here is one for Circle:
<gml:CircleByCenterPoint
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:gml="http://www.opengis.net/gml" xmlns:xlink="http://www.w3.org/1999/xlink" xsi:schemaLocation=" http://www.opengis.net/gml http://schemas.opengis.net/gml/3.1.1/base/geometryPrimitives.xsd" numArc="1"> <gml:pos srsName="urn:ogc:def:crs:OGC:1.3:CRS84">115.832 -31.939</gml:pos> <gml:radius uom="km">0.5</gml:radius> </gml:CircleByCenterPoint> One could remove the srsName if we know the default is WGS 84. Also note
the flexibility of expressing the "uom" - units of measurement. the "uom" allows
the application to express the units of measure in just about any units.
Here is a "richer" GML document for Polygon. This is what is used by
the OGC OpenLS Core Specification as well as by OMA in the MLP API Spec.
<INWATERA_1M.GEOMETRY>
<gml:Polygon srsName="EPSG:4326">
<gml:exterior>
<gml:LinearRing
srsName="EPSG:4326">
<gml:coordinates
decimal="."
cs=","
ts="">119.593002319336,-31.6695003509522
119.595306396484,
31.6650276184082
119.600944519043,-31.6658897399902
119.603385925293,-31.669527053833
119.60050201416,-31.6739158630371
119.595664978027,-31.6728610992432 119.593002319336,
31.6695003509522</gml:coordinates>
</gml:LinearRing>
</gml:exterior>
</gml:Polygon>
</INWATERA_1M.GEOMETRY>
This is a bit "rich" in terms of semantic content. However,
this GML example would support the expression of islands (holes) in the
polygon geometry. If islands are not an issue, the GML could be reduced
to:
<gml:Polygon srsName="EPSG:4326">
<gml:LinearRing>
<gml:coordinates
decimal="."
cs=","
ts="">119.593002319336,-31.6695003509522
119.595306396484,
31.6650276184082
119.600944519043,-31.6658897399902
119.603385925293,-31.669527053833
119.60050201416,-31.6739158630371
119.595664978027,-31.6728610992432 119.593002319336,
31.6695003509522</gml:coordinates>
</gml:LinearRing>
</gml:Polygon> Again, the srsName could be ignored. Also, for expressing the
srsName, we could use an OGC URN liternal along the lines of srsName=”urn:ogc:def:crs:EPSG:6.6:4326”>
These example obviously do not have the external references,
such as xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance".
Now for a point. Can't get much simpler
than this! This example is from the new OGC GML Point Profile document - well on
its way to becoming an OGC standard.
<gml:Point
srsName=”urn:ogc:def:crs:EPSG:6.6:4326”> <gml:pos>45.256
-110.45</gml:pos> </gml:Point> Carl Reed, PhD
CTO and Executive Director Specification Program OGC The OGC: Helping the World to Communicate Geographically
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