Aeronautical Information Exchange Model (AIXM) – GML Encoding Guidelines

Copyright EUROCONTROL 2011 Objective Guidelines for aviation specific aspects E.g. srsName (WGS 84 is imposed in aviation) E.g. Surface and lines - specials Parallels Arcs E.g. Embedded curves/points Geographical borders re-used in Surface definitions In relation with the use of AIXM for aeronautical data encoding GML Profile

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Copyright EUROCONTROL 2011 Positions - encoding … … First latitude, then longitude ICAO Annex 15, all “published aeronautical geographical coordinates (indicating latitude and longitude) shall be expressed in terms of the WGS-84 geodetic reference datum”

Copyright EUROCONTROL 2011 Lines and surfaces No explicit indication of the type of interpolation between two points Assumed “Straight lines” Unless same latitude -> assumed “parallel” 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.

Copyright EUROCONTROL 2011 Straight lines gml:Geodesic gml:GeodesicString … …

Copyright EUROCONTROL 2011 Parallels Linear interpolation -> parallel Longitude axis Latitude axis (NORTH) Lat 1 Long1 Lat 1 Long2 Linear interpolation in a geodetic CRS

Copyright EUROCONTROL 2011 Arc by centre point lat_P3 long_P3 radius calculated_start_angle calculated_end_angle gml:ArcByCenterPoint

Copyright EUROCONTROL 2011 Re-calculate centre If necessary for spatial calculations!

Copyright EUROCONTROL 2011 Arc by edge gml:Arc … … P2 P3 P4... Can we not change our practices? Use Arc by edge! -Less ambiguous -No problems with projections -Perfectly supported in GIS tools

Copyright EUROCONTROL 2011 Circle gml:CircleByCenterPoint

Copyright EUROCONTROL 2011 Other suggested subjects Wind Spiral

Copyright EUROCONTROL 2011 Airspace aggregation By reference - between synchronized databases By copying the geometry - geometrical data for direct consumption Combined if necessary

Copyright EUROCONTROL 2011 Point references * Edge point * Centre point * Etc. “E) AIR DISPLAY WILL TAKE PLACE WI LATERAL LIMITS: N E (NDB OBR) N E (VILLAGE JAKOVO) N E N E (NDB OBR). gml:pointProperty

Copyright EUROCONTROL 2011 With annotation VILLAGE JAKOVO information provided is “for human consumption”

Copyright EUROCONTROL 2011 With xlink:href Local Remote references as well to the feature! Looking into other xlink attributes… include xlink:title for display purpose

Copyright EUROCONTROL 2011 Progress Initial version November 2010 after ADWG meeting in Brussels Task for the Aviation Domain WG Current version (0.6) GMLGuidelinesForAIXMhttp://external.opengeospatial.org/twiki_public/AviationDWG/ GMLGuidelinesForAIXM 80% mature, still to do: GML profile details (exact list of GML elements) interpolation/densification issues (should this be in?) Other geometries (wind spiral, etc. ?) Target: finalise end 2011 Release during TC meeting in March 2012 as “Discussion paper” (March 2012)

Copyright EUROCONTROL 2011 & Q A & Q A

Copyright EUROCONTROL 2011 Other issues – accuracy, resolution, integrity

Copyright EUROCONTROL 2011 Other issues – data quality ICAO, European ADQ Regulation (73/2010) Data accuracy Data publication resolution Data integrity Problems Understanding of requirements Different interpretations by different people Pre-imposition of some technical solutions Such as use of CRC Lack of direct support in GML But maybe there was a good reason for that

Copyright EUROCONTROL 2011 Data accuracy AIXM extension of GM_Point, GM_Curve, GM_Surface also, use of Metadata for global values (data set, feature)

Copyright EUROCONTROL 2011 Data publication resolution

Copyright EUROCONTROL 2011 Data publication resolution AIXM business (data verification) rules, but: GML lat /long format is not DDMMSS.ssss! No place in AIXM/GML for specifying the precision of an individual x or y position in gml:pos or gml:posList Although explicitly required by ICAO We can use metadata for global values - data set level or feature level Need to treat lat/long position as character string, not as numbers! Preserve trailing zeros Pay attention to database conversions In: Out: 23: (not OK!)

Copyright EUROCONTROL 2011 Data integrity ICAO Annex 15, Point “Electronic aeronautical data sets while stored or in transit shall be protected by the inclusion in the data sets of a 32-bit cyclic redundancy check (CRC) implemented by the application dealing with the data sets. This shall apply to the protection of all integrity levels of data sets as specified in (critical, essential and routine data).” ADQ IR, Annex VI (1) “All data transferred in an electronic format shall be protected against loss or alteration of data by the application of the CRC32Q algorithm as referred to in point 21 of Annex III. The cyclic redundancy check (hereinafter CRC) value shall be applied before the final verification of the data prior to storage or transfer.”

Copyright EUROCONTROL 2011 CRC - guidelines operational principles AIXM 5.1 support extension

Copyright EUROCONTROL 2011 The VERY IMPORTANT question 1.Do we need to allocate a CRC value when the data is originated and preserve (store/transmit) that same CRC value along the whole data chain, up to the end user? Or 2.Is it OK if CRC are used just for data in transit, meaning that they are calculated 'on the fly' when the data is packed for transmission, checked at the other end and then dropped?

Copyright EUROCONTROL 2011 Option 1 - CRC “per data record” Data merging – re-calculate CRCV!

Copyright EUROCONTROL 2011 AIXM 5.1 – proposed encoding AIXM Extensions Each AIXM Feature CRC “subjects” - xPath expression Would also work if option 2 is chosen Just allow multiple elements! … //aixm:ARP//gml:pos | //aixm:ARP//aixm:elevation | 582C2727 …

Copyright EUROCONTROL 2011 AIXM 5.1 – proposed solution General principle Use xpath to indicate which elements are included If complex elements are indicated, all their content is included Several CRCV per feature supports both Option 1 and Option 2 CRC algorithm specification Metadata? Extension? Any known ‘list of values’?

Copyright EUROCONTROL 2011 & Q A & Q A