[x3d-public] Latitude/Longitude units

Andreas Plesch andreasplesch at gmail.com
Wed Apr 13 06:30:11 PDT 2016


Good point. Section 25.2.4 could be read that way as it does point out that
the angle unit is a choice.

The problem with using angle standard units is that authors would want to
use radians for orientations and rotations but at the same time degrees for
latitude/longitude. In my experience radians is very rarely used as a unit
for geodetic coordinates. The only example example I can think of is in
equations.

Some options:

1) no changes to the spec., modify examples
2) prescribe degrees as unit for geodetic coordinates in section 25.2.4
3) add a standard unit for angular distance in Table 4.2 (
http://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/concepts.html#t-Standardunits)
with a default of degrees and refer to that in 25.2.4

My preference would be option 2), followed by 3).

Therefore I propose that in section 25.2.4, second paragraph:

" Latitude and longitude are given in units of angle base units. The
following assumes an angle base unit of degrees. If a UNIT statement for
angle base units has been provided, the following values for latitude
and/or longitude should be suitable converted to that angle base units."

shall be replaced by:

" Latitude and longitude are given in units of degrees."

for simplicity.

Andreas


On Wed, Apr 13, 2016 at 6:21 AM, Holger Seelig <holger.seelig at yahoo.de>
wrote:

> My interpretation was that with version 3.3 the UNIT statement defines
> what unit a angle value has. And therefore on default the angles of
> geodetic coordinates should be in radians. The author has then with the
> UNIT statement the choice to define its preferred angle unit.
>
> Holger
>
> Am 13.04.2016 um 06:16 schrieb Andreas Plesch:
>
>>
>> http://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/components/geodata.html#Specifyinggeospatialcoords
>>
>> defines that coordinates in the GD geoSystem are given in angular base
>> units.
>>
>>
>> http://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/concepts.html#t-Standardunits
>>
>> defines the standard angle unit to be radians.
>>
>> Cobweb interpretes this to mean latitude/longitude in geoCoords are
>> given in radians which I think should not be the intention of the spec.
>> All geospatial example scenes use degrees. So I hope this is a
>> misinterpretation.
>>
>> Although section 25.2.4 as linked goes on to assume that the base
>> angular unit is degrees, it is a bit unclear what unit is really expected.
>>
>> If more precise language is needed, I suggest simply to add "angular
>> base units of degrees" to section 25.2.4 .
>>
>> Andreas
>>
>>
>
> --
> Holger Seelig
> Mediengestalter Digital – Digital Media Designer
>
> Scheffelstraße 31a
> 04277 Leipzig
> Germany
>
> Cellular: +49 1577 147 26 11
> E-Mail:   holger.seelig at create3000.de
> Web:      http://titania.create3000.de
>
> Future to the fantasy ★ ★
>



-- 
Andreas Plesch
39 Barbara Rd.
Waltham, MA 02453
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