[Geotiff] Vertical Coordinate Systems in .las, GeoTIFF and WKT

[Max Martinez]

Frank,

The description of your approach doesn't surprise me (sounds very
reasonable) but I wondered how you envisioned dealing with the
"ellipsoidal height" issue which is compounded (no pun intended) by the
use of GeoTIFF.

The issue is that I didn't think EPSG/ISO 19111/OGC support vertical
coordinate systems based on ellipsoidal height. Although the original
OGC specification may have allowed these vertical datum types, ISO
19111/OGC AT 2 does not and I don't believe it is possible to have a
standard vertical coordinate system of this type in the EPSG database.
This not only makes it impossible to describe a projected coordinate
system with ellipsoidal height, but also causes problems in the purely
geographic case (because you still can't do 2d geographic + vertical
based on ellipsoid). Are you envisioning people using the 3d geographic
crs codes and omitting the vertical information? 

This has been a topic before on the GeoAPI mailing lists (which
continues to support a geoidal vertical datum type even in their
proposed 3.0 version which is intended for OGC standardization) but
remains somewhat unresolved. Roel Nicolai was involved in that
discussion but I didn't quite get a satisfactory answer for why it has
been eliminated from the model. I've attached that conversation (in case
I'm being dense).

I don't know if it is an issue for las data, but in the general
promotion of the vcs information in GeoTIFF, it is likely to come up and
cause interoperability issues unless an explicit statement is made about
how to handle lat, lon, ellipsoidal height and whether to and how to
handle projected + ellipsoidal height in geotiff. (And, what happens
when translating from WKT [where it is expressible] to GeoTIFF in these
cases)?

Max

-----Original Message-----
From: geotiff-bounces at lists.maptools.org
[mailto:geotiff-bounces at lists.maptools.org] On Behalf Of Frank Warmerdam
Sent: Monday, January 11, 2010 1:51 PM
To: metacrs at lists.osgeo.org; GeoTIFF
Subject: [Geotiff] Vertical Coordinate Systems in .las, GeoTIFF and WKT

Folks,

I have recently done some work on vertical cs support in the .las
(lidar)
format.  LAS uses geotiff tags for georeferencing, and liblas also
returns
OGC WKT representations of coordinate system.

I have prepared a web page on my efforts, the first portion of which
(down
about as far as "Sample Data") may be of broader interest.

The support for vertical coordinate systems is already covered in the
OGC CT specification (01-009) and the GeoTIFF specification, but in my
opinion little use has been made of this in the past.  So I'm interested
in feedback on my approach, and I'm hoping it can help as we move to
support vertical coordinate systems more widely in GeoTIFF, and other
coordinate system projects.

   http://liblas.org/wiki/VerticalCS

Best regards,
-- 
---------------------------------------+--------------------------------
------
I set the clouds in motion - turn up   | Frank Warmerdam,
warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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Subject: Re: [GeoAPI.wg] Compound CRS Question: Does 2D Projected +Ellipsoidal Height not make sense?
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