Straight Line

Owned by Wolfgang Scheucher
Last updated: 2021 Mar 25

The gml:GeodesicString shall be used as default encoding for straight lines. The reasons are:

  • A geodesic interpolation is the mathematical generalization of the notion of “straight line” on the surface of the Earth;
  • The result of the interpolation on the surface of the Earth does not depend on the CRS used; by contrast, a linear interpolation would result on different curves on the surface of the Earth, depending on the CRS used (in fact, this will be exploited in order to encode lines along a parallel, see further down).

The pairs of lat/long coordinates can be encoded as either a sequence of gml:pos or, more compact, using a gml:posList element:

<aixm:Surface gml:id="S01" srsName="urn:ogc:def:crs:EPSG::4326">
	<gml:patches>
		<gml:PolygonPatch>
			<gml:exterior>
				<gml:Ring>
					<gml:curveMember>
						<gml:Curve gml:id="C001">
							<gml:segments>
								<gml:GeodesicString>
									<gml:posList>52.18556 5.20833 52.20611 5.2875 52.18917
									5.29889 52.16917 5.29889 52.18556 5.20833</gml:posList>
								</gml:GeodesicString>
							</gml:segments>
						</gml:Curve>
					</gml:curveMember>
				</gml:Ring>
			</gml:exterior>
		</gml:PolygonPatch>
	</gml:patches>
</aixm:Surface>