[Esip-documentation] Geospatial Bounds

[Aleksandar Jelenak via Esip-documentation]

Hello John,

On 10/1/14, 1:44 PM, “John Graybeal"
<esip-documentation at lists.esipfed.org> wrote:
>I did have a few simple questions.
>
>
>1) Do I correctly understand that the height of EPSG 4979 is GPS height,
>that is, above the ellipsoid that GPS uses?

Yes.

>2) If it's really true that the ranges of the geospatial limits are
>approximate values (first I've heard that), shouldn't we say that in
>their definitions?

I think “approximate values” was introduced to reflect the possibility
those values may not strictly reflect the geospatial extent of the data in
the file. I am fine if others support removing this term because it can be
confusing.

>3) DId you mean to say this attribute must always use this vertical
>datum?  Or just that this is the default?

Always. If it’s default then we would need a way to specify the actual
coordinate reference system and currently that is not possible in ACDD. We
would either need another attribute for that or adopt the non-standard
Extended WKT format.

>I'm OK with it if people want this attribute to always use ellipsoidal
>height, but I suspect many applications will only have the height
>above/below the actual surface (for example, Instantaneous Water Level,
>EPSG 5113).

The geospatial_bounds attribute’s role is to broadcast data’s geospatial
extent to metadata cataloging systems. If the data is in some other CRS
then it is up to the data producer (creator) or publisher to translate
that geospatial extent to the WGS-84 2D or 3D CRSs for this attribute. To
me that is a more reasonable requirement then to expect metadata discovery
systems to know all the possible CRSs.

	-Aleksandar