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Copyright © 2012Open Geospatial Consortium
Geometry Ad Hoc – Introduction to Aviation Use Cases and Requirements
80th OGC Technical Committee
Austin, Texas (USA)
Johannes Echterhoff (iGSI)
March 20, 2012
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Outline
• Background• Overview• CurveSegment Types currently considered by GML Profile• Issues• Summary
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Background
• Certain AI features have polygonal shape, e.g. Airspace• Published in AIP (Aeronautical Information Publications), e.g.:
EAP 25 (The Castle) 52°11'08.00"N 005°12'30.00"E;52°12'22.00"N 005°17'15.00"E; 52°11'21.00"N 005°17'56.00"E; 52°10'09.00"N 005°17'56.00"E;(then along the parallel to) 52°10'09.00"N 005°13'11.00"E;to point of origin.
• Curve interpolation not specified explicitly, but usual assumption is that:– Line connecting two consecutive points with same lat is a parallel on
surface of the earth (can also be explicitly stated)– Otherwise line considered to be „shortest line“ – map projection used
for design typically unknown
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Background
• Arcs of circle also used, e.g. in airspace border definition:EHR 4A (VLIEHORS) TSA 53°10'12.59"N 004°46'21.14"E; along clockwise arc (radius 8 NM, centre 53°15'00.00"N 004°57'00.00"E) to 53°07'01.98"N 004°56'02.41"E; 53°11'00.00"N 004°51'24.00"E; to point of origin
– Arc center is sometimes a distance measuring equipment that enables to keep a “constant radius”, best approximated as a geodesic distance
• Airspace corridors – like a buffer around a curve – are also used.
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Background - Needs
• Define/design lines, arcs, circles using GUI (usually 2D)• Retain semantics:
– Line interpolation: • geodesic, rhumbline/loxodrome – independent of projection• linear – depends on projection
– Arc / circle interpolated on earth surface, not in 2D• For arc/circle defined by center point: radius defines geodesic distance from
center point to control points
• Support encoding of corridors.
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Overview
• AIXM 5 based on ISO 19107 and ISO 19136 (GML 3.2.1)
• Profile of full GML functionality to support Aviation needs described in „Use of GML for aviation data“ document– available on pending docs– to become DP Aviation DWG, March 22
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CurveSegment Types currently considered by GML Profile
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CurveSegment Types currently considered by GML Profile (simplified)
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Issues – CurveInterpolationType Encoding
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GM_CurveInterpolationType (property of GM_CurveSegment) is codelist, but in ISO 19136 it is not extensible.
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Issues – Definition of XXByCenterPoint
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• Added by ISO 19136, not defined by ISO 19107 • Semantics insufficiently defined• Interpolation fixed to
circularArcCenterPointWithRadius• Per GML: only usable in 2D!
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Issues – Semantics of GM_Arc / GM_Circle
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• Interpolation fixed to circularArc3Points• Underspecified? Circle interpolated how – in
projection space or on surface of the earth?
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Issues – Support for Loxodrome/Rhumbline
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• Rhumbline/loxodrome only straight line in World Mercator• Rhumbline interpolation not well supported by ISO 19107 /
19136– No specific code in CurveInterpolationType– No specific type that could use that code (all have fixed interpolation)
• Current workaround is to use LineString with World Mercator projection (still problematic near poles)
Image source: http://en.wikipedia.org/wiki/Rhumb_line
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Issues – OffsetCurve
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Image source: http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Attributes-Stroke.html
• Currently not usable for airspace corridor encoding• Offset distance: geodesic or not?• Clarify semantics: correct interpretation of offset distance
for curve segments that are not straight lines:
• Clarify case of sudden direction change(different join styles?):
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Issues – Corridor/Buffer
• Airspace corridor actually a buffer around base curve? Define new „CurveBuffer“, „Corridor“ or general „(Geodesic)Buffer“ type?– Buffer available as GM_Object operation but not as actual type for
encoding.– Buffer operation underspecified? Distance – geodesic or not?– Different end styles?
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Image source: http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Attributes-Stroke.html
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Summary - Needs
• Define/design lines, arcs, circles using GUI (usually 2D)• Retain semantics:
• Line interpolation: – geodesic, rhumbline/loxodrome – independent of projection– linear – depends on projection
– Arc / circle interpolated on earth surface, not in 2D• For arc/circle defined by center point: radius defines geodesic distance
from center point to control points
• Support encoding of corridors.
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Summary - TODOs
• Revise CurveInterpolationType in ISO 19136 to make it code list – CR submitted for GML – OGC doc 08-194
• Support in both ISO 19107 / ISO 19136 for:– ArcByCenterPoint, CircleByCenterPoint,
„GeodesicArcByCenterPoint“, „GeodesicCircleByCenterPoint“– Clarify semantics for GM_Arc, GM_Circle interpolation
(circularArc3Points)– Support rhumblines/loxodromes new XX_Loxodrome type +
interpolation– Corridor/Buffer encoding
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