Can someone please tell me what the status is of http://www.ietf.org/internet-drafts/draft-ietf-geopriv-relative-location-01.txt? It seems that the last revised draft was submitted on March 28, but there has been no follow-on activity or discussion related to it.
I would be happy to pick-up this thread, if it is proper for me to do so, not having any previous involvement with this group. I will be attending the OGC CityGML SWG in Sept., so was hoping to learn more about how they are modeling relative location with the objective of using some of their thinking to inform the specification of relative location in PIDF-LO. Guess what I am struggling with a bit at the moment is how much information is proper for the PIDF-LO, and how much should be provided by services referenced in the object.
I guess what still seems most mysterious to me at this point is how (and when) a target location is placed in the context of a World Coordinate Reference System. I suppose the map document reference used for this could be put in the PIDF-LO by the localization application, assuming that all of this was planned in advance. But I wonder about the case where a team must respond to an address for an emergency, so must discover whether a map document or BIM exists for it, along with the method of localization used (if one exists). In other words, it seems like search of a catalog or registry might be required. In either case, I think that instantiation of a PIDF-LO requires localization and contextualization applications that retrieve information and perform computations with it, and while these applications are implicit in the current draft, I'm not sure that the PIDF-LO as specified facilitates this data flow. Is it others' understanding that the secondary map data/metadata would be provided by the localization service?
Then there's that huge "hairball" related to "shapes of uncertainty." My feeling on this is that, if you feel the need to include some measure of location uncertainty in the PIDF-LO, then you should either provide the shape and the location of its boundary for an agreed-on uncertainty value (e.g., 5% error), or provide a shape (and the location of its boundary) with its uncertainty value. However, if all you are trying to convey is that a target is located somewhere within a space bounded by well-known building features, e.g., an office, presumably the coordinates of the boundary would be derived from a map document, e.g., a floorplan or BIM, and these would convey location uncertainty, e.g., I am only certain that Joe is in the main conference room but I can't tell you exactly where he is in it.
At any rate, I have provided more detailed comments below to 22 excerpts, referenced by section in the current draft. I would gladly engage others in clarifying these points, and would be happy to talk to people at the OGC meetings in Sept. about any questions or outstanding issues related to this draft.
Regards,
Cliff Behrens
=============== Comments Follow Below ===============================================
Section 1
(1) The reference location can also have dynamic components such as velocity. The relative offset is specified in meters using a Cartesian coordinate system.
Does this belong in the object? If so, should it have orientation (and in Cartesian coordinates)? Does this make sense indoors?
(2) Applications could use this information to display the relative location. Additional fields allow the map to be oriented and scaled correctly.
Shouldn’t this be data or metadata either stored with the referenced document or in a catalog that references it?
Section 3
(3) ...and the reference location could specify a point within the building from which the offset is measured.
If one were to determine location in this manner, then wouldn’t it be desirable to also specify how localization was determined and its accuracy? (See localization generator or LG in GML 3.1.1 PIDF-LO Shape Application Schema for use by the Internet Engineering Task Force.)
(4) The baseline location SHOULD be general enough to describe both the reference location and the relative location (reference plus offset). In particular, ....., etc.
This is kind of murky...a figure would help.
(5) If the baseline location was expressed as a geodetic location, the reference MUST be geodetic. If the baseline location was expressed as a civic address, the reference MUST be a civic. Baseline and reference locations MAY also include dynamic location information [RFC5962].
Seems this constraint is unnecessary if a detailed BIM were obtained for a civic address, and then used to determine geodetic locations from BIM + localization. Why would the baseline location ever change?
(6) The relative location can be expressed using a point (2- or 3-dimensional), or a shape that includes uncertainty: circle, sphere, ellipse, ellipsoid, polygon, prism or arc-band. Descriptions of these shapes can be found in [RFC5491].
Seems a red-herring if you don’t quantify it. Again, this might be determined based on localization technique.
(7) Optionally, a reference to a 'map' document can be provided. The reference is a URI.
How/when is this association made?
(8) The document could be an image or dataset that represents a map, floorplan or other form. The type of document the URI points to is described as a MIME media type.
Including a CityGML BIM.gml.
(9) Metadata in the relative location can include the location of the reference point in the map as well as an orientation (angle from North) and scale to align the document CRS with the WGS-84 CRS.
Again, wouldn’t this alignment best be made with metadata stored with the referenced document? If all of this look-up and alignment is driven by an application, then can’t it also get the metadata for the document and use these to align it and locate the reference point in it?
(10) The document is assumed to be useable by the application receiving the PIDF with the relative location to locate the reference point in the map. This document does not describe any mechanisms for displaying or manipulating the document other than providing the reference location, orientation and scale.
It shouldn’t have to. It should only provide the URI to the application which uses the PIDF-LO.
(11) xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
This needed for localization or Location Geneator?
(12) xmlns:ca="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
Why is IETF using own specification for civic addresses rather than OASIS xNAL standard, as used by OGC?
(13) xmlns:gs="http://www.opengis.net/pidflo/1.0"
Is all of this still relevant given revisions to this draft?
(14) <rel:map>
<rel:url type="image/png">
http://example.com/location/map.png
</rel:url>
<rel:offset>20. 120.</rel:offset>
<rel:orientation>29.</rel:orientation>
<rel:scale>20. -20.</rel:scale>
</rel:map>
I can well imagine a use case where all of this is discovered through an application using civic or geodetic address and knowledge of LG.
Section 4
(15) Relative location is a shape (point, circle, ellipse...). The shape is defined with a CRS that has a datum defined as the reference (which appears as a civic address or geodetic location in the tuple), and the shape coordinates as meter offsets North/East of the datum measured in meters (with an optional Z offset relative to datum altitude). An optional angle allows the reference CRS be to rotated with respect to North.
Datum, baseline location, reference location, relative location...need to be more carefully defined and distinguished, along with the implications for each when applied to civic and geodetic addresses. Isn’t “elevation” a better term since it refers to height above geoid (or sea level) rather than height above ground?
4.2
(16) Dynamic location information [RFC5962] in the baseline or reference location alters relative coordinate system. The resulting Cartesian coordinate system axes are rotated so that the 'y' axis is oriented along the direction described by the <orientation> element. The coordinate system also moves as described by the <speed> and <heading> elements.
Not sure this makes sense. Shouldn’t the baseline location, at least, remain fixed since it may be the only datum stored for a building through which one can associate WRS and LCS?
4.9
(17) Shape data is used to represent regions of uncertainty for the reference and relative locations. Shape data in the reference location uses a WGS84 [WGS84] CRS. Shape data in the relative location uses a relative CRS.
This makes little sense unless either (a) an uncertainty value is used to compute a shape, or (b) an uncertainty measure is provided for a shape. Otherwise, if a shape is used to provide an approximate location for a target, e.g., somewhere in an office room, then presumably a floorplan or BIM (with the proper shape and coordinate values) would be used to provide the geospatial context for target location.
4.9.2
(18) A circle or sphere describes a single point with a single uncertainty value in meters.
Don’t see where uncertainty value is provided in the example below (i.e., 4.9.2.1).
4.9.3
(19) A ellipse or ellipsoid describes a point with an elliptical or ellipsoidal uncertainty region.
Why doesn’t this shape also have associated with it an uncertainty value (like the circle), especially if this is the reason for providing a shape?
4.9.4
(20) A polygon or prism include a number of points that describe the outer boundary of an uncertainty region.
...and what is its value?
4.9.5
(21) A arc-band describes a region constrained by a range of angles and distances from a predetermined point. This shape can only be provided for a two-dimensional CRS.
Why is uncertainty not a property of this shape?
4.10
(22) Maps can be simple images, vector files, 2-D or 3-D geospatial databases, or any other form of representation understood by both the sender and recipient.
I would include a BIM, e.g., a CityGML model, in this list of representations. But how is this reference added to the PIDF-LO? I would also like to provide a link to a catalog service that provides a map or model for a civic or geodetic location. The catalog service would supply appropriate metadata, e.g., CRS, publication data, datum or “baseline location”, etc. for the document.
-- Clifford Behrens, PhD Senior Scientist & Director Information Analysis Applied Research Telcordia Technologies, Inc. Phone: 732-699-2619 FAX: 732-336-7015 Email: cliff@research.telcordia.com
