Geogrid Map Projection / Input DEM Question

[Kayla Yamamoto]

Hi all,

Does anyone know if the input geographical datasets need to be in a specific CRS/projection to work with the WPS Geogrid program?  

I checked some of the index files for the default elevation datasets I used in the past, and it looks like they use a regular lat-lon projection ('regular_ll').

I read that WPS supports Lambert conformal conic, polar stereographic, Mercator, Cylindrical Equidistant projected coordinate systems, but am having trouble getting my input DEM to work with Geogrid.  Geogrid completes, but the 'HGT_M' variable is 0 throughout the domain.

My DEM is provided in UTM NAD83 (PA11) and I am using a 'lambert' map projection for my model domain.  

Do I need to reproject my DEM to a different CRS before converting to WPS binary?

Any information is greatly appreciated!

Thank you,

Kayla

[Kevin]

Kayla,

According to the WPS documentation, the supported projections for WPS tiles are:

• lambert
• polar
• mercator
• regular_ll
• albers_nad83
• polar_wgs84

It sounds like some of your input datasets (such as elevation for the 'HGT_M' variable) are not correctly specified, or the path is not found for the tiles. 

I typically use the QGIS plugin called "GIS4WRF" which can convert an raster dataset (selected as the active layer) into a set of WPS binary tiles. I am not sure if the utility can convert from UTM to one of the supported coordinate systems, so you may need to check the index file that comes out of that utility in order to confirm the coordinate system and units makes sense. 

Thanks,

Kevin

[Kayla Yama]

Hi Kevin,

It doesn't look like the UTM projection is compatible with the GIS4WRF plugin.  The utility allows me to convert to WPS binary tiles and produces an index file without error, but when run with Geogrid it gives values of zero throughout my domain.  From the index file created, I can see that it reads the DEM as a regular 'mercator' projection and also specifies 'stdlon = inf' which doesn't look correct.

I ended up just reprojecting my DEM to one of the supported crs from the documentation you linked and that appears to have solved the problem!

Thanks,

Kayla

[Kevin Sampson]

Kayla,

I suspected that the GIS4WRF utility may have issues with certain projected coordinate systems. Glad to hear you found a pathway to generate the WPS tiles and create a geogrid file with your data!

Kevin

Kevin Sampson, GISP
Associate Scientist
National Center for Atmospheric Research
P.O. Box 3000 Boulder, CO  80307-3000
Tel: 303.497.8121