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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

OGC®

Outline

• Background• Overview• CurveSegment Types currently considered by GML Profile• Issues• Summary

Copyright © 2012Open Geospatial Consortium 2

OGC®

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


OGC®

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.


OGC®

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.


OGC®

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


OGC®

CurveSegment Types currently considered by GML Profile


OGC®

CurveSegment Types currently considered by GML Profile (simplified)


OGC®

Issues – CurveInterpolationType Encoding


GM_CurveInterpolationType (property of GM_CurveSegment) is codelist, but in ISO 19136 it is not extensible.

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OGC®

Issues – Definition of XXByCenterPoint


• 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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OGC®

Issues – Semantics of GM_Arc / GM_Circle


• Interpolation fixed to circularArc3Points• Underspecified? Circle interpolated how – in

projection space or on surface of the earth?

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OGC®

Issues – Support for Loxodrome/Rhumbline


• 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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http://en.wikipedia.org/wiki/Rhumb_line

http://en.wikipedia.org/wiki/Rhumb_line

OGC®

Issues – OffsetCurve


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?):

http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Attributes-Stroke.html



OGC®

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?


Image source: http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Attributes-Stroke.html




OGC®

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.


OGC®

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


https://portal.opengeospatial.org/files/?artifact_id=31244




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