[georss] elevation question

[Joshua Lieberman]

Sean,

I think the situation is pretty similar. Most features are coded into  
KML as 2D, with an option to plot at a certain level or just "stick"  
to the ground. There is an increasing but still limited use of   
features with 3D tuples, mostly in the form of models for buildings  
and other infrastructure. There are some 3D tracks being published in  
KML, but things like storm tracks I think are often published at some  
single plausible level above the terrain and may also use the  
"relativetoGround" option.

Come to think of it, we might want to have a georss option which lets  
whatever elevatiion data is provided be better interpreted by GE and  
other 3D programs (e.g. absolute, relative, or clamped / zero  
relative). In principle the CRS could take care of this as well, but  
I'm not sure there is any easy way of specifying the vertical datum to  
be whatever terrain model is being used.

--Josh



On Apr 8, 2008, at 10:03 AM, Sean Gillies wrote:

> Why does GeoRSS recommend using 'georss:elev' over 3D tuples? 3D is
> working out pretty well for KML.
>
> Joshua Lieberman wrote:
>> No, that is not the case.
>>
>> If you have a single elevation generally associated with the item,  
>> you
>> can put that in the georss:elev or georss:floor property. As a
>> property, it doesn't belong inside georss:where alongside an object
>> such as gml:Point. Only one georss:where is supported per entry and
>> one geometry (for now) per georss:where element, so there is no
>> ambiguity.
>>
>> If you have a need for a more complicated representation, as you
>> describe, then you are free to reference or specify a 3D / 4D / 5D
>> coordinate reference system (CRS) and supply multidimensional tuples
>> for every node, in accordance with ISO and OGC specifications for GML
>> geometries as supported in the gmlgeorss profile. Then you can  
>> specify
>> elevations for separate nodes on a linestring as you describe.
>>
>> Cheers,
>>
>> Josh
>>
>> On Apr 8, 2008, at 1:05 AM, Makc wrote:
>>
>>> so, what you're saying is that elevation can no longerbe associated
>>> neither with individual shapes (since it does not go inside
>>> <georss:where>), not to mention individual vertices, and instead is
>>> only available for whatever the parent item is in the XML, i.e.  
>>> only 1
>>> elevation per item?
>>>
>>> so, for example, a line with two vertices one at 1m and other at 10m
>>> elevation is not representable in georss/gml format?
>>>
>>> On Tue, Apr 8, 2008 at 3:51 AM, Joshua Lieberman <josh at oklieb.net>
>>> wrote:
>>>> The schema updated for w3c geo 2007 makes georss:elev an  
>>>> independent
>>>> attribute at the same level as georss:where, e.g.
>>>>
>>>>> <georss:where>
>>>>> <gml:point>
>>>>>  <gml:pos>blah blah</gml:pos>
>>>>> </gml:point>
>>>>> </georss:where>
>>>>>
>>>>> <georss:elev>313</georss:elev>
>>>>>
>>>> Same in Georss Simple:
>>>>
>>>> <georss:point>42.213 -133.123</georss:point>
>>>>
>>>> <georss:elev>313</georss:elev>
>>>>
>>>> The schema for both of these is described at
>>>> http://www.georss.org/xml/1.1/overview . The site needs some more
>>>> updates,
>>>> etc.
>>>>
>>>> Cheers,
>>>>
>>>> Josh
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> On Apr 7, 2008, at 8:33 PM, Raj Singh wrote:
>>>>
>>>>>
>>>>>
>>>>> On Apr 7, 2008, at 4:34 PM, Makc wrote:
>>>>>
>>>>>> I have also found xsd file at
>>>>>> http://www.georss.org/xml/1.0/georss.xsd, where elevation lands
>>>>>> under
>>>>>> whereAttrGroup. I am not too good with these xsd things, but my
>>>>>> interpretation is that, whenever someone wants to use  
>>>>>> elevation, it
>>>>>> has to go inside <georss:where> together with <gml:something>,  
>>>>>> like
>>>>>>
>>>>>> <georss:where>
>>>>>> <gml:point>blah blah</gml:point>
>>>>>> <georss:elev>313</georss:elev>
>>>>>> </georss:where>
>>>>>>
>>>>>> and not, for example, like
>>>>>>
>>>>>> <georss:where>
>>>>>> <georss:point>blah blah</georss:point>
>>>>>> <georss:elev>313</georss:elev>
>>>>>> </georss:where>
>>>>>>
>>>>>> which does not really make sense to me, but it's like what it  
>>>>>> looks
>>>>>> like ...
>>>>>>
>>>>> The XSD you reference only applies to GeoRSS GML
>>>> (http://www.georss.org/gml
>>>>> ).
>>>>> There's no schema for GeoRSS Simple. In GeoRSS GML you would  
>>>>> write:
>>>>> <georss:where>
>>>>> <gml:point>
>>>>>  <gml:pos>blah blah</gml:pos>
>>>>> </gml:point>
>>>>> <georss:elev>313</georss:elev>
>>>>> </georss:where>
>>>>>
>>>>> I can't help with figuring out which one is right for Simple...
>>>>>
>>>>> ---
>>>>> Raj
>>>>> _______________________________________________
>>>>> georss mailing list
>>>>> georss at lists.eogeo.org
>>>>> http://lists.eogeo.org/mailman/listinfo/georss
>>>>>
>>>>
>>
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