Meeting: 6 May 2003

[Eliot Christian <echristi@usgs.gov>]

GIS SC Meeting Notes of 6 May 2003

The meeting was conducted via conference call. Participants were:

Donald Thomas (Blue292, Inc.)
Rex Brooks (individual)
Bill Schroder (ESRI)
Eliot Christian (U.S. Department of the Interior)

Eliot reported that David Denko (ESRI) was not able to participate.
David had sent an e-mail concerning the action he had taken from
the last meeting. "After looking into it we decided it would be
best not to use the subset of (GML) geometry classes from the Open
Location Service Specification. But we will develop a direct subset
of GML geometry and provide it to the group in an XML Schema."

David also asked for further clarification from the CAP community:
"What we really need to know first is what the CAP requirements are.
 From the example, it's a simple message with some pretty simple
geometries, we can add a third dimension by just adding an elevation
to the position information. I was thinking a polygon, of course,
but also multiple polygons, perhaps a line, an envelope (box), a
point and radius, and a point - what else? How accurate do these
positions have to be? We need to know all the uses for CAP.  For
explicit communication its usually best if everyone used decimal
degrees in a common reference system (WGS 84) but to we need to
be more flexible? Will it ever be used for high detail position
information?"

The participants on today's call agreed to take a close look at the
CAP format with respect to its GIS-related elements. The immediate
objective would be to make explicit in CAP documentation all of the
implicit assumptions and constraints associated with the geometric
elements (e.g., What projection is used as the base? How are
coordinate transforms achieved from/to other geometries? What
accuracy and precision are implied by the given geometry?, Are
there inherent ambiguities and how are these expected to be handled?)

It was also discussed that there may well be suggestions as to
enhancements or additional optional elements that might be advisable
for inclusion in CAP. For example, a pair of optional elements
could be included to delineate elevation, perhaps as a base and
ceiling given in feet displaced from mean sea level.

Those on the call agreed to send to all participants their notes
on review of the CAP format, in addition to the comments expected
from David's action.