Hi Christian There are three main reasons that you use a local coordinate system for most 3D application:
1. Z buffer performance in most 3D renderers. 2. Avoiding rounding error issues relating to navigation and camera control. 3. File bloat. Google Earths' KML/Collada files are typically 40% oversized, in my tests, due to the use of lat/long descriptions for each vertex. Typically, we work in UTM, WGS 84 with a local coordinate system for each city. It's important to do 3D city work in UTM so that square buildings remain square. Some systems use a per building local coordinate system. I find this art path to be very awkward. David Colleen Planet 9 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
