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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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- as angle values have an unlimited range, the flattened circle is a theoretically unlimited line.
Wiki Markup each angle (from \[0°,360°\]) on the circle has an unlimited number of representations: _angle + X * 360°, X being an integer_- to define arcs on a circle, it is important that the difference between end and start angle is smaller than 360°: |end-angle - start-angle| < 360° (else the result would be an arc that is greater than or equal to 360° and looks like a circle)
- computing the length of an arc can be performed as follows: |startAngle – endAngle|/180° * radius * pi - the definition conforms to this formula
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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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