Re: WCS - server and client presentation

• To: Norman Barker <nbarker@xxxxxxxxx>
• Subject: Re: WCS - server and client presentation
• From: John Caron <caron@xxxxxxxxxxxxxxxx>
• Date: Tue, 21 Jun 2005 15:28:45 -0600

Hi Norman:

Norman Barker wrote:

Hi John,

thanks for the mail, I hope you are well. I have answered your questions inline below, please ask more if you want. We are treating this very much as learning, knowledge sharing exercise.

Q. netcdf files - are you assuming CF conventions for georeferencing?

A. We are, and we aren't. The only place where are input files aren't CF compliant is the timestamp, and we have placed the format of this in an external properties file so we can change it. Our input files are CF compliant apart from this

Q. multiband geotiff - what did you map into the multiple bands?

A. We have mapped the vertical dimension (geoZ) of the netCDF file into the bands. Using the describeCoverage RangeSet elements we were able to put a lookup between the bands, 0,1,...27 to the actual z-levels values from the netCDF file, and our client shows meaningful values rather than band numbers. I can send you parts of the

describeCoverage XML if you like when I am in back in the office.

is there any information in the geotiff as to the meaning of the bands?

Q. do you pregenerate the geotiff or generate on the fly?

A. We pregenerate the netCDF file because we have used Java and MapServer is in C. However you make an interesting point, I wonder by using python whether I could hook an 'on the fly' conversion using your libraries?

Q. do you use "data sample" geotiff format, or greyscale or ??

A. We use 16bit floating point geotiff format, so the values of the netCDF file are preserved. This is the same format as USGS use for DEM geotiffs.

Q. Can you handle a request that has multiple times and/or vertical levels?

A. We can handle a request that has multiple levels no problem, since it is possible to request different bands of a geotiff using MapServer WCS, so our client converts from the metadata description in describeCoverage of the z-levels to the band numbers before making the request, so it can ask for &bands=1,4,5,6 say. We can only request a single time, since it is one geotiff file per time. However the describe coverage lists the temporal dimension correctly (as per the WCS spec) and the Key Value pair added to the request is &time=YYYY... It would be good to be able to request multiple times, and perhaps zip them up before downloading to the client. However for the display, downloading per single timestep gives a more interactive feel.

ok, thanks for the info!

Norman Barker