Hi, Maybe this helps:
If you have 3 points and you specify them with x, y values and their values on some 2D spatial reference system relative to an origin are: 100, 200 101, 200 102, 200 If you set a new relative origin at 100, 200, then all you need store for the points is: 0, 0 1, 0 2, 0 In this example you do not win a lot, and it will depend on the nature of the numbers used (precision and range etc), but I hope it helps imagine instances when it helps greatly. Furthermore, again depending on the calculations done with the numbers, error caused by imprecise calculations will tend to be less with less extreme numbers. So, one reason is to reduce storage, another is to cope with imprecision. Best wishes, Andy http://www.geog.leeds.ac.uk/people/a.turner/ -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Christian Willmes Sent: 01 September 2009 19:21 To: Ron Lake Cc: geojson; [email protected]; GeoRSS Subject: Re: [Geowanking] [georss] [Geojson] simple 3D geocode for AR Hi all, Maybe I don't understand what you talking about the necessity to use local coordinate systems, so can one please clarify to me, why one can't (or should not) model - as precisely as you just want - every single (not moving) point on earth in a Geocentric Spatial Reference Frame [1]? I see that actually the process of 3D modelling and grouping of objects in systems with a own origin makes sense, but I can't see why a computer can't do the same mathematical operations on numbers with just some more digits? Maybe I'm just blocked on that issue in the moment... :-/ Thanks and regards Christian [1] http://www.euclideanspace.com/threed/solidmodel/geospatial/geocentric/index.htm Ron Lake schrieb: > You will need other local coordinate systems. > > R > > -----Original Message----- > From: Mike Liebhold [mailto:[email protected]] > Sent: August 31, 2009 5:13 PM > To: Chris Goad > Cc: Christian Willmes; Ron Lake; geojson; [email protected]; > GeoRSS > Subject: Re: [Geowanking] [georss] [Geojson] simple 3D geocode for AR > > H'mm. all great thoughts, mostly about camera focal planes grids, > pattern matching and spatial query formulations, > > I'm still thinking more about the geocoded media, created for AR. > > How will these sometimes sometimes huge, often, very small, data chunks > > describe their precise 3D postion, for -- maximum discovery-- > > by the maximum number of crawlers, for yet to be invented fossgeo ar > clients , .com ar clients like layar and mobilzy, and 1000 more to > follow shortly, 3D map clients like google earth and bing [cringe], VR > worlds, mmorpgs, the whole web, etc. > > Maybe it's just a URI including lat.lon.elev....crs... ? > > now wondering if the location semantics in the URI could be as plain > language simple as a delicious, facebook or twitter URL. > > > ? > > Chris Goad wrote: > >> There is a substantive issue here to do with local coordinate >> systems. When representing the features of a particular object it is >> sometimes useful to employ coordinates local to that object, and >> represent separately the position of the object in the world or >> relative to its parent in a heirarchy. Reasons: The coordinates of >> features relative to the object may be known more accurately than >> global position of the object, and an AR device's relative position to >> > > >> the object might also be known with greater precision than its global >> position. The object may not have a fixed position (eg AR on board a >> ship). The representation is more compact. >> >> 3d modeling formalisms support this (and full GML does too), but >> GeoRSS, GeoJSON, and KML do not. This is probably an argument for >> going to represententations built for 3d in the first place for AR >> applications where local coordinates play a necessary role, but >> concievably there is a niche for our lightweight geo standards >> extended by addition of a transformation node. >> >> >> -- Chris >> >> ----- Original Message ----- From: "Christian Willmes" >> <[email protected]> >> To: "Mike Liebhold" <[email protected]> >> Cc: "Ron Lake" <[email protected]>; "geojson" >> <[email protected]>; <[email protected]>; "GeoRSS" >> <[email protected]> >> Sent: Friday, August 28, 2009 6:00 PM >> Subject: Re: [Geowanking] [georss] [Geojson] simple 3D geocode for AR >> >> >> >>> Hi, >>> >>> whats the problem here? Its simple coordiante transformation stuff... >>> > > >>> or do I miss something?! >>> >>> The device gets the geocoordinates from the web, and computes those >>> using its own position and orientation to local camera >>> > coordinates.... > >>> its that simple... I think. ;-) >>> >>> regards, >>> Christian >>> >>> Mike Liebhold schrieb: >>> >>>> Ron Lake wrote: >>>> >>>>> The most logical coordinate >>>>> system for locating such items is a rectilinear coordinate system >>>>> (x-y-z >>>>> frame) centered (origin) at the focal point of the camera. >>>>> >>>> What's the use case? >>>> >>>> In most cases, we probably can assume that the geo-annotations exist >>>> > > >>>> independent of the viewpoint; e.g. a viewer should be able to see >>>> the note attached to a restaurant from any perspective as they pass >>>> on a sidewalk, or drive by. >>>> >>>> In that case, we need absolute coordinates, not relative to the >>>> camera perspective. >>>> >>>> imho >>>> >>>> Mike >>>> >>>>> Cheers >>>>> >>>>> Ron >>>>> >>>>> >>>>> -----Original Message----- >>>>> From: Mike Liebhold [mailto:[email protected]] Sent: August 28, 2009 >>>>> 2:05 PM >>>>> To: Ron Lake >>>>> Cc: Joshua Lieberman; [email protected]; geojson; GeoRSS >>>>> Subject: Re: [georss] [Geojson] simple 3D geocode for AR >>>>> >>>>> Ron Lake wrote: >>>>> >>>>>> The use of geographic coordinates for [location of things in the >>>>>> field >>>>>> >>>>> of view relative to the camera] likely does not. [ make sense] >>>>> >>>>> Ron, >>>>> >>>>> This is really counter intuitive, Can you explain what you mean? >>>>> >>>>> - Mike >>>>> >>>>>> -----Original Message----- >>>>>> From: [email protected] >>>>>> [mailto:[email protected]] On Behalf Of Joshua >>>>>> > Lieberman > >>>>>> Sent: August 28, 2009 11:03 AM >>>>>> To: [email protected] >>>>>> Cc: geojson; GeoRSS >>>>>> Subject: Re: [georss] [Geojson] simple 3D geocode for AR >>>>>> >>>>>> In both GeoRSS GML and GeoJSON, some explicit CRS needs to be >>>>>> specified to use 3-coordinate locations. The simplest one for >>>>>> GeoRSS seems to be epsg:4979 ( urn:ogc:def:crs:EPSG:4979 ). It >>>>>> would need a slight modification to support the GeoJSON long-lat >>>>>> encoding. Otherwise use GeoRSS Simple and the elev property. >>>>>> >>>>>> e.g. >>>>>> >>>>>> <georss:elev>346</georss:elev> >>>>>> <georss:point>42.3234 -173.234134</georss:point> >>>>>> >>>>>> Well-known text description of 4979 >>>>>> (http://spatialreference.org/ref/epsg/4979/ ) >>>>>> GEOGCS["WGS 84", DATUM["World Geodetic System 1984", SPHEROID["WGS >>>>>> >>>>> 84", >>>>> >>>>>> 6378137.0,298.257223563, AUTHORITY["EPSG","7030"]], >>>>>> AUTHORITY["EPSG","6326"]], PRIMEM["Greenwich",0.0, >>>>>> AUTHORITY["EPSG","8901"]], UNIT["degree",0.017453292519943295], >>>>>> AXIS["Geodetic latitude",NORTH], AXIS["Geodetic longitude",EAST], >>>>>> AXIS["Ellipsoidal height",UP], AUTHORITY["EPSG","4979"]] >>>>>> >>>>>> Josh >>>>>> >>>>>> On Aug 28, 2009, at 1:05 PM, Ron Lake wrote: >>>>>> >>>>>> >>>>>>> Sorry my example should have been >>>>>>> >>>>>>> <Point id = "P1" CRS = "http://www.blah.bla/standardCRS.xml";> >>>>>>> <coordinates>100 200 150</coordinates> >>>>>>> </Point> >>>>>>> >>>>>>> But the argument is the same. Similar encodings can be made in >>>>>>> > JSON > >>>>>>> etc. >>>>>>> >>>>>>> R >>>>>>> >>>>>>> -----Original Message----- >>>>>>> From: [email protected] >>>>>>> [mailto:[email protected]] On Behalf Of Andrew >>>>>>> > Turner > >>>>>>> Sent: August 28, 2009 9:57 AM >>>>>>> To: [email protected]; GeoRSS; geojson >>>>>>> Subject: Re: [georss] [Geojson] simple 3D geocode for AR >>>>>>> >>>>>>> Simplest? >>>>>>> >>>>>>> Just include a 3rd coordinate in GeoRSS-Simple point or GeoJSON >>>>>>> >>>>> point. >>>>> >>>>>>> No, this is not explicitly valid. But you see where that >>>>>>> > discussion > >>>>>>> gets us. Long windy roads of elusive semantic talk (arguably >>>>>>> >>>>> necessary >>>>> >>>>>>> in the lon term, but not simple or useable *now*, which is when >>>>>>> >>>>> people >>>>> >>>>>>> are building these tools). >>>>>>> >>>>>>> If we lose interest without achieving a near term concensus, >>>>>>> developers will just do arbitrary, different solutions. Give them >>>>>>> > a > >>>>>>> simple answer now, even if it makes your >>>>>>> > strict-validation-only-skin > >>>>>>> crawl just a little bit. :) >>>>>>> >>>>>>> So I say just do it, and we'll catch up with documenting it as >>>>>>> > uses > >>>>>>> emerge. >>>>>>> >>>>>>> Also, KML already supports 3D points. >>>>>>> >>>>>>> Andrew >>>>>>> >>>>>>> >>>>>>> >>>>>>> (via mobile) >>>>>>> >>>>>>> On Aug 27, 2009, at 4:35 PM, Mike Liebhold <[email protected]> wrote: >>>>>>> >>>>>>> >>>>>>>> A friend wrote me with a request for clarification on a topic >>>>>>>> > we've > >>>>>>>> discussed many times here, but every time we've approached a >>>>>>>> consensus the answer seems elusive. >>>>>>>> >>>>>>>> Many devleopers are starting to create applications for iPhones >>>>>>>> > and > >>>>>>>> Android phones to view location specific data through the >>>>>>>> viewfinder using the -imprecise- capabilities of the built in >>>>>>>> > gps > >>>>>>>> and compass and applications platforms like Layar. >>>>>>>> >>>>>>>> The question: >>>>>>>> >>>>>>>> What is the -simplest- way to geocode a geoannotation in 3D >>>>>>>> > using > >>>>>>>> geoRSS/Atom, geojson, KML ....? >>>>>>>> >>>>>>>> (Is there a practical reason why WGS '84 shouldn't be implicit, >>>>>>>> > and > >>>>>>>> a CRS lookup NOT be required?) >>>>>>>> >>>>>>>> >>>>>>>> _______________________________________________ >>>>>>>> Geojson mailing list >>>>>>>> [email protected] >>>>>>>> http://lists.geojson.org/listinfo.cgi/geojson-geojson.org >>>>>>>> >>>>>>> _______________________________________________ >>>>>>> georss mailing list >>>>>>> [email protected] >>>>>>> http://lists.eogeo.org/mailman/listinfo/georss >>>>>>> _______________________________________________ >>>>>>> georss mailing list >>>>>>> [email protected] >>>>>>> http://lists.eogeo.org/mailman/listinfo/georss >>>>>>> >>>>>> _______________________________________________ >>>>>> georss mailing list >>>>>> [email protected] >>>>>> http://lists.eogeo.org/mailman/listinfo/georss >>>>>> _______________________________________________ >>>>>> georss mailing list >>>>>> [email protected] >>>>>> http://lists.eogeo.org/mailman/listinfo/georss >>>>>> >>>>>> >>>>>> >>>>> >>>> _______________________________________________ >>>> Geowanking mailing list >>>> [email protected] >>>> http://geowanking.org/mailman/listinfo/geowanking_geowanking.org >>>> >>> _______________________________________________ >>> Geowanking mailing list >>> [email protected] >>> http://geowanking.org/mailman/listinfo/geowanking_geowanking.org >>> >> > > _______________________________________________ Geowanking mailing list [email protected] http://geowanking.org/mailman/listinfo/geowanking_geowanking.org _______________________________________________ Geowanking mailing list [email protected] http://geowanking.org/mailman/listinfo/geowanking_geowanking.org
