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Specifics About Map Projection

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catalinaporaicu

New member
Hello,

I am trying to figure out the exact projection of my geogrid output. I have attached my namelist.wps file below. However, this information is not sufficient, and I would like to know the exact ellipsoid shape that WRF uses.

Perhaps if I explain what I am trying to do with WRF/WRF-Chem, my question will be more clear. Essentially, I am trying to complete some WRF runs in the exact same projection as some input data, which will later be used in the WRF-Chem anthropogenic emissions preprocessor. I do not wish to manipulate this data, as I would like it to contain as much of the original information as possible, so I am trying to alter the WRF grid so that it is identical to the data projection. The projection of my data is (taken from the shapefile of my data, in QGIS):

+proj=lcc +lat_1=50.85 +lat_2=50.85 +lat_0=50.85 +lon_0=3.67 +x_0=0 +y_0=0 +ellps=intl +towgs84=-106.869,52.2978,-103.724,0.3366,-0.457,1.8422,-1.2747 +units=m +no_defs

As you can see, the ellipse used by my data projection is international, and there is a datum transformation to WGS84.

I was wondering if there is a solution within the WRF or WPS namelists to give more information to the projection? Or perhaps the code can be altered in some way to input my options? Any help is very appreciated!

Thanks in advance.
 

Attachments

  • namelist.wps
    1.3 KB · Views: 87
Hi,
Based on your namelist.wps file, the projection is 'lambert,' which is a basic Lambert Conformal projection. There should be plenty of available resources online regarding this projection type. You can also find a bit of information in this slide presentation, given at our WRF Users' Tutorial:
https://www2.mmm.ucar.edu/wrf/users/tutorial/202001/duda_wps_general.pdf
 
Hello,
Thanks for the response. I know the projection is Lambert, because I have set it myself in the namelist. I am looking for more information on the projection that WRF uses -- what ellipsoid does it use? Does it use a datum transformation? I understand the projection type but I don't see where to obtain this exact information for the model. The simple Lambert Conformal projection information is not sufficient for what I need the model to do.
Let me know if there is anywhere to obtain this detailed information. Maybe in the code somewhere? In order for ij/latlon grid to be created, there must be some calculation done with regards to the projection, with more information than that input in the namelist.wps
 
Does anyone know the WRF projection in the Proj.4 format? I am wondering about the exact projection, which takes into consideration things like the shape of the ellipsoid of the earth, radius of the earth, flattening of the earth, datum, units, scale factor, etc.

I need to manually project some input data in order to use it in WRF, so I need as much information regarding the WRF projection as possible. I would like to have the projection information in the following format (written for an example projection):
+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +datum=OSGB36 +units=m +no_defs
https://spatialreference.org/ref/epsg/27700/proj4/

I will do this in Python, so that is why I would like to have this format.
 
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