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Ben, Thanks for your kind remarks, and for your clarification. However, your clarifications seems to have one thing backwards. A DerivedCRS is specified by a coordinate conversion from a baseCRS to that DerivedCRS. I think of the DerivedCRS being in the evenly-spaced index CRS, with the baseCRS having data at unevenly-spaced pressure levels. Arliss _____ From: bendomenico@xxxxxxxxx [mailto:bendomenico@xxxxxxxxx] On Behalf Of Ben Domenico Sent: Wednesday, March 25, 2009 5:48 PM To: Whiteside, Arliss E (US SSA) Cc: wcs-1.2.swg@xxxxxxxxxxxxxxxxxxxxxxxx; Unidata GALEON Subject: Re: [WCS-1.2.swg] March 25 Teleconference Minutes Arliss, That's an excellent summary of what was a very informative and useful telecon for me. It touched on nearly all the major issues that arose as a result of GALEON 1 experiments. One clarification I would add is noted under item 4 in your summary below. I am going to take the liberty of forwarding a copy of this to the GALEON list because many of them will be interested and are not on the WCS SWG list. I look forward to even more fruitful discussions of these topics at the OGC TC meeting next week. Many thanks. -- Ben On Wed, Mar 25, 2009 at 5:59 PM, Whiteside, Arliss E (US SSA) <arliss.whiteside@xxxxxxxxxxxxxx> wrote: March 25 Teleconference Attendees: (not a quorum) Steven, Keens, PCI Geomatics Arliss Whiteside, BAE Systems Wenli Yang, George Mason University Max Martinez, ERDAS, Inc. Peter Baumann, Jacobs University Bremen Ben Domenico, National Center for Atmospheric Research (observer) John Herring, Oracle (observer) Summary: As chair, Steven moderated this teleconference. We discussed only one planned topic: Generalized Domain: allowing non spatio-temporal axes in domain. 1) Arliss noted that the email traffic indicated that the proposed generalized domain, although useful for other purposes, may not be needed for: a) Allowing use of a pressure domain dimension, if the WCS domain supported the ISO 19111-2 extension allowing (only one) parameterized axis. b) Allow a second time domain dimension, if the second time axis is represented in the coverage range. Ben said he needs to consider this possibility further. 2) Steven asked if the domain axes need to be independent. Arliss stated that the coverage domain is now defined by a BoundingBox in a referenced CRS, and that the axes of all CRSs must be independent per ISO 19111. 3) Ben stated that a pressure domain dimension would be independent of horizontal position (e.g., latitude and longitude). This pressure is an atmospheric pressure, where its relationship to elevation (above sea level) or height (above ellipsoid) may vary some with horizontal position. More significantly, sample points in a pressure domain dimension are not evenly spaced. Ben said they also frequently use non-even spacings of grid points in the horizontal axes (e.g., latitude and longitude). They also sometimes use point clouds, not grids. 4) Non-even spacing of grid points in any domain dimension is a WCS problem, for both a parameterized axis (per ISO 19111-2) and the proposed generalized domain. Arliss said that non-even spacing seems to require WCS to define how to specify a grid coverage domain in a CRS with one or more dimensions without evenly spaced points. One possible way would be to define a DerivedCRS that is used as the baseCRS of the coverage GridCRS. Such a DerivedCRS would use a coordinate Conversion from its baseCRS, and a coordinate Conversion can be based on a table of corresponding values. By definition, a coordinate Conversion is error-free. Ben's note: there was specific mention of a possible coordinate conversion being from a baseCRS that is in index space to a spatial or parametric coordinate where the baseCRS is the index into at table that gives the values of the coordinate points. The particular example we consered was the list of unevenly-spaced pressure levels that serve as the vertical coordinate points for many fields in the output of forecast models. This example is important for the met-ocean community in two ways. First ISO the 19111-2 extension apparently allows us to work with parametric coordinates (e.g., pressure); second the DerivedCRS described above provides a mechanism for handling uneven grid spacing. 5) Interpolation between non-even spaced grid points in a pressure domain dimension would require special interpolation methods. However, interpolation between grid points is often not desired by clients of such data, and that can be handled by specifying "none" WCS interpolation. 6) Max suggested that this SWG delay a decision on Generalized Domain until we find a clear need. Many persons present agreed that this decision could be delayed. Arliss Whiteside _______________________________________________ WCS-1.2.swg mailing list WCS-1.2.swg@xxxxxxxxxxxxxxxxxxxxxxxx https://lists.opengeospatial.org/mailman/listinfo/wcs-1.2.swg
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