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GML implements the semantics of ISO 19107. As such, the semantics for an angle encoded in GML is given by ISO 19107 clause:
"In this variant of Bearing usually used for 2D coordinate systems, the first angle (azimuth) is measured from the first coordinate axis (usually north) in a counterclockwise fashion parallel to the reference surface tangent plane."
General Direction of Increasing and Decreasing Angle Values
ISO 19107 thus 19107 thus defines in which direction angle values increase and in which direction they decrease - see the following diagram:
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| Code Block | ||||||
|---|---|---|---|---|---|---|
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<gml:ArcByCenterPoint numArc="1">
<gml:pointProperty>
<gml:Point gml:id="ID1">
<gml:pos>0 0</gml:pos>
</gml:Point>
</gml:pointProperty>
<gml:radius uom="m">1</gml:radius>
<gml:startAngle uom="deg">actual_start_value</gml:startAngle>
<gml:endAngle uom="deg">actual_end_value</gml:endAngle>
</gml:ArcByCenterPoint> |
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Therefore, it is recommended to interpolate ArcByCentrePoint through points situated at equal geodesic distance (the radius of the arc) from the arc centre. This makes the interpolation independent of the CRS used.
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