Hi Kerry,

That sounds like a bizarre problem.

MGET actually has two sampling tools. The traditional one, called Sample Rasters, internally uses Sample tool from the ArcGIS Spatial Analyst toolbox. Thus it would not be surprising for MGET’s Sample Rasters and Spatial Analyst’s Sample to behave in the same way. Is that what you are seeing?

The newer MGET sampling tool is called Interpolate Raster Values At Points. We developed this one because we found Sample Rasters was just too slow. Interpolate Raster Values reads raster values directly with GDAL and does not rely on any ArcGIS tools, the main bottleneck. Could you try that one and see if you get the same results? If it gives the expected values (not what Sample is giving), it might suggest that ArcGIS is having trouble reading the rasters, while GDAL is not. That would be strange, but might be possible.

If that doesn’t work—if Interpolate Raster Values agrees with Sample—then something else is going on. I would check:

·         Did you assign a spatial reference system to the rasters (via Define Projection) and is it correct?

·         Do the points also have a spatial reference system?

·         When you overlay the points on the raster in ArcMap, do they appear in the correct place? Presumably this is what you did when you queried the rasters using the information button, but if not, it is always good to check this.

If that still won’t work, I can take a deeper look. Send me the instructions on getting the netCDF file and send me some of your points and I’ll try to reproduce the problem.

Best,

Jason

Hi,

I am having a problem getting the sample raster tool in MGET to sample my rasters. To be honest I think it is a problem with the raster not the tool but perhaps you can advice.

Basically I have downloaded the NetCDF file for global ocean temperature from the NOAA website, I have used Arc tool box to convert the NetCDF file to a raster and made separate rasters for each depth band in the NetCDF file. Now I am trying to sample each depth band temp raster using a point file and MGET. However, when I do this it returns data for some points and no data (-999999) for others. When I query the rasters using the information button in GIS the correct values are there but for some reason the tool wont sample them?

Any ideas? It does this if I use the Arc tool box sample single raster tool too.

Many thanks

Kerry

Dr Kerry Howell

Davy 622,

Marine Biology and Ecology Research Centre,

The Marine Institute at Plymouth University,

School of Marine Science and Engineering,

Drakes Circus,

Plymouth.

PL4 8AA

+44(0)1752 584544

Please note I am not at work on Wednesday or Thursday after 1:30.