1. ® Hosted and Sponsored by 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

2. OGC ® Outline Background Overview CurveSegment Types currently considered by GML Profile Issues Summary Copyright © 2012Open Geospatial Consortium2

3. 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 Copyright © 2012Open Geospatial Consortium3

4. 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. Copyright © 2012Open Geospatial Consortium4

5. 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. Copyright © 2012Open Geospatial Consortium5

6. 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 Copyright © 2012Open Geospatial Consortium6

7. OGC ® CurveSegment Types currently considered by GML Profile Copyright © 2012Open Geospatial Consortium7

8. OGC ® CurveSegment Types currently considered by GML Profile (simplified) Copyright © 2012Open Geospatial Consortium8

9. OGC ® Issues – CurveInterpolationType Encoding Copyright © 2012Open Geospatial Consortium GM_CurveInterpolationType (property of GM_CurveSegment) is codelist, but in ISO 19136 it is not extensible. 9

10. OGC ® Issues – Definition of XXByCenterPoint Copyright © 2012Open Geospatial Consortium Added by ISO 19136, not defined by ISO 19107 Semantics insufficiently defined Interpolation fixed to circularArcCenterPointWithRadius Per GML: only usable in 2D! 10

11. OGC ® Issues – Semantics of GM_Arc / GM_Circle Copyright © 2012Open Geospatial Consortium Interpolation fixed to circularArc3Points Underspecified?  Circle interpolated how – in projection space or on surface of the earth? 11

12. OGC ® Issues – Support for Loxodrome/Rhumbline Copyright © 2012Open Geospatial Consortium 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_linehttp://en.wikipedia.org/wiki/Rhumb_line 12

13. OGC ® Issues – OffsetCurve Copyright © 2012Open Geospatial Consortium13 Image source: http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Attributes-Stroke.htmlhttp://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?):

14. 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? Copyright © 2012Open Geospatial Consortium14 Image source: http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Attributes-Stroke.htmlhttp://tavmjong.free.fr/INKSCAPE/MANUAL/html/Attributes-Stroke.html

15. 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. Copyright © 2012Open Geospatial Consortium15

16. OGC ® Summary - TODOs Revise CurveInterpolationType in ISO 19136 to make it code list –CR submitted for GML – OGC doc 08-194OGC 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 Copyright © 2012Open Geospatial Consortium16