[x3d-public] [X3D-Public] camera, random path on a sphere

[Andreas Plesch]

Don,

I had the same expectation but it turns out that all implementations I have seen just linearly interpolate. For small distances it does not matter much. For larger distances it does mean travelling underground in case of a GC geosystem but not in the case of the default GD geosystem where just latitude and longitude and elevation are interpolated independently.
We had an exchange on the geospatial list at the time which I can dig up.
So I believe the original intention was just linear interpolation, and 'in the spatial reference frame' means output of coordinates consistent with the key values. However, I would support a change to great circle interpolation as it is probably expected by authors.

Andreas

On November 29, 2015, at 10:53 PM, Don Brutzman <brutzman at nps.edu> wrote:

>On 11/29/2015 5:08 PM, Andreas Plesch wrote:
>> On November 29, 2015, at 2:01 PM, x3d-public-request at web3d.org wrote:
>>[...]
>> John,
>>
>> I added an SFBool option onGreatCircle for GeoPositionInterpolator in x3dom when I implemented the node. This is non-standard. The standard says somewhere that interpolators interpolate linearly.
>>
>> Not sure how this can be used in a non-geospatial scene, however, especially without a script node. I guess you could use the geocentric geoSystemand wrap the viewpoint in a transform to scale it down to how you need it. For example, to get positions on a sphere of 10  m radius you would need to divide coordinates by ca. 637000.
>>
>> It might also work to  just provide non-geospatial coordinates to GeoPositionInterpolatorwith the GCgeoSystemas long as they are located on a sphere centered at the origin. The interpolated coordinates should still be on the same sphere.
>>
>> Cobweb does not support geospatial last time I checked.
>onGreatCircle sounds like an interesting addition... though wondering what would be the alternative?
>==============================
>25.3.7 GeoPositionInterpolator
>http://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/components/geodata.html#GeoPositionInterpolator
>[...]
>The geovalue_changed field outputs the the interpolated coordinate in the spatial reference frame specified by geoSystem. This can be passed to other GeoX3D nodes that support a field of this form (e.g., GeoViewpoint and GeoLocation).
>==============================
>I would interpret "in the spatial reference frame" to imply great-circle travel, since dipping underground is usually suboptimal...
>Sounds like a good topic for geospatial working group to consider.  Please submit a spec comment if there are plausible alternatives that such a field might indicate.  Thanks for your efforts.
>all the best, Don
>-- 
>Don Brutzman  Naval Postgraduate School, Code USW/Br       brutzman at nps.edu
>Watkins 270,  MOVES Institute, Monterey CA 93943-5000 USA   +1.831.656.2149
>X3D graphics, virtual worlds, navy robotics http://faculty.nps.edu/brutzman