[x3d-public] [geospatial] Latitude/Longitude units
Holger Seelig
holger.seelig at yahoo.de
Thu Apr 14 04:00:06 PDT 2016
As I can see, most of all agree and as it is usual, that long/lat are in
degree. That's an important point and I will easily switch over to it,
for the over all compatibility and conformance.
Holger
Am 13.04.2016 um 19:04 schrieb Andreas Plesch:
> Holger, I tend to agree but I think it is an unfortunate, perhaps
> unintended consequence of introducing the UNIT statement which needs to
> be addressed.
>
> There is a little bit of wiggle room. The UNIT statement and Table 4.2
> talk about angle _standard_ units while section 25.2.4 talks about angle
> _base_ units. So angle _base_ units may be different from angle
> _standard_ units. I am not sure if such a distinction was intentional
> when the spec. language was authored but it may have been and then not
> fully followed through.
>
> v 3.2 of the spec. just prescribes units of degrees while Table 4.2 has
> radians as standard angle unit. We should just go back to that.
>
> Andreas
>
> http://www.web3d.org/documents/specifications/19775-1/V3.2/Part01/components/geodata.html#Specifyinggeospatialcoords
> http://www.web3d.org/documents/specifications/19775-1/V3.2/Part01/concepts.html#t-Standardunits
>
>
>
>
>
> On Wed, Apr 13, 2016 at 10:51 AM, Holger Seelig <holger.seelig at yahoo.de
> <mailto:holger.seelig at yahoo.de>> wrote:
>
> The specification in 3.3 is absolutely exact at this point. The
> assumption that the base unit is in degree refers to to the range
> values specified. If the assumption would be radians then the
> corresponding values would be given. That mean in 3.3 the default
> angle unit for long/lat are radians.
>
>
> 25.2.4 Specifying geospatial coordinates
>
> 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. Latitude is in the range −90..+90, and longitude can be
> in the range −180..+180 or 0..360 (0 deg longitude is the same point
> in both cases).
>
>
> Holger
>
>
>
>
>
>
>
> Am 13.04.2016 um 16:33 schrieb Roy Walmsley:
>
> Thanks for this great discussion. I can see that text
> modifications are
> likely to be required here.
>
> In addition, I would like to raise a related question. In 25.2.4
> Specifying geospatial coordinates, the ‘GD’ option allows either
> “latitude_first” or “longitude_first”, the order being
> controlled by the
> /geosystem/ field. There is no other specific mention of an option
> within the geosystem field to specify either of these. Should
> there be?
> Or is it automatically determined by the choice of ellipsoid
> from Table
> 25.3?
>
> Under the UTM option the option of “easting_first” or
> “northing_first”
> is an analogous case. What is the answer for this case?
>
> Roy
>
> *From:*geospatial [mailto:geospatial-bounces at web3d.org
> <mailto:geospatial-bounces at web3d.org>] *On Behalf Of
> *Andreas Plesch
> *Sent:* 13 April 2016 14:30
> *To:* Holger Seelig
> *Cc:* geospatial at web3d org; X3D Graphics public mailing list
> *Subject:* Re: [geospatial] Latitude/Longitude units
>
> 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 <mailto:holger.seelig at yahoo.de>
> <mailto:holger.seelig at yahoo.de <mailto: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 <tel:%2B49%201577%20147%2026%2011>
> <tel:%2B49%201577%20147%2026%2011>
> E-Mail: holger.seelig at create3000.de
> <mailto:holger.seelig at create3000.de>
> <mailto:holger.seelig at create3000.de
> <mailto:holger.seelig at create3000.de>>
> Web: http://titania.create3000.de
>
> Future to the fantasy ★ ★
>
>
>
>
> --
>
> Andreas Plesch
> 39 Barbara Rd.
> Waltham, MA 02453
>
>
>
> --
> Holger Seelig
> Mediengestalter Digital – Digital Media Designer
>
> Scheffelstraße 31a
> 04277 Leipzig
> Germany
>
> Cellular: +49 1577 147 26 11 <tel:%2B49%201577%20147%2026%2011>
> E-Mail: holger.seelig at create3000.de <mailto:holger.seelig at create3000.de>
> Web: http://titania.create3000.de
>
> Future to the fantasy ★ ★
>
>
>
>
> --
> Andreas Plesch
> 39 Barbara Rd.
> Waltham, MA 02453
--
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 ★ ★
More information about the x3d-public
mailing list