<div dir="ltr"><div><div><div><div><div><div>Hi Stavros,<br><br></div>To the best of my knowledge, the masking functions are unaware of any cartographic projections in the data, and so both grid and shapefile need to be in the same coordinate system. I would guess your shapefile is in lat/lon? NCL has an unadvertised interface to the well-known projection library Proj4 -- if you know the projection parameters of your stereographic grid, you could use the proj4 interface to convert the grid to lat/lon. The function is:<br><br></div> transform_coordinate(srcProj:string, dstProj:string, x:double, y:double, z:double)<br><br></div>where the src/dstProj are proj4 descriptors of the source/destination projections. The coordinates are passed in and transformed out through the x,y,z arrays (I can get you started if you send me the grid's metadata describing the projection).<br><br></div>As for speeding up the process, one strategy I've used in the past is, for coastal nations that have many small islands (relative to the grid resolution), exclude those. Shapefiles have an "area" variable, and magnitude of that value will be vastly larger than those for islands. So by inspecting the data, you get a feel for which shapefile polygons are the ones "of interest", and you can select those out, and then use the gc_inout() function to perform the masking. Alternatively, if you have access to GIS software like ArcGIS, you could do the same culling operations (likely much easier!) to create such a paired-down shapefile, and then use shapefile_mask_data() as before.<br><br></div>Hope that helps...<br></div>Rick<br></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Oct 18, 2017 at 4:33 AM, Stavros Dafis <span dir="ltr"><<a href="mailto:sdafis@cc.uoi.gr" target="_blank">sdafis@cc.uoi.gr</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Dear NCL users,<br>
<br>
I have a set of netcdf files with snow, land and sea variables and the<br>
projection is Polar Stereographic ellipsoidal (WGS-84 ellipsoid). I have<br>
plotted an example remapped to a Mercator projection:<br>
<a href="https://ibb.co/mFZAd6" rel="noreferrer" target="_blank">https://ibb.co/mFZAd6</a><br>
<br>
I would like to mask the data only inside the shapefile of Greece, but I cannot<br>
figure out why the "shapefile_mask_data" keeps the wrong values. This is what I<br>
get:<br>
<a href="https://ibb.co/iyBZ5m" rel="noreferrer" target="_blank">https://ibb.co/iyBZ5m</a><br>
<br>
How is it possible to cut the values in another projection than the initial?<br>
<br>
This is part of the code for masking:<br>
<br>
shp_filename1 = "/data/dafis/Greek_shape/GRC_<wbr>adm1.shp" ; State outlines<br>
<br>
opt = True<br>
;opt@delta_kilometers = 2<br>
;opt@minlat = minlat<br>
;opt@maxlat = maxlat<br>
;opt@minlon = minlon<br>
;opt@maxlon = maxlon<br>
opt@debug = True<br>
opt@shape_var = "NAME_0"<br>
opt@shape_names = "Greece"<br>
;opt@return_mask = True<br>
opt@keep = True<br>
<br>
snow_mask = shapefile_mask_data(snow,shp_<wbr>filename1,opt)<br>
<br>
The whole procedure takes 5 minutes for one day and I have 6205 days to compute.<br>
I read in this thread that is normal to take so long to run, due to the complex<br>
coastline:<br>
<a href="https://www.ncl.ucar.edu/Support/talk_archives/2014/0728.html" rel="noreferrer" target="_blank">https://www.ncl.ucar.edu/<wbr>Support/talk_archives/2014/<wbr>0728.html</a><br>
<br>
Any suggestions? The opt@minlat/lon etc does not help to plot faster.<br>
<br>
Has anyone succeeded in speeding up the procedure or do you know where I can<br>
find coarse shapefiles for countries since I mostly care about excluding the<br>
neighbor countries and not the sea.<br>
<br>
<br>
--<br>
Stavros NTAFIS (DAFIS)<br>
------------------------------<wbr>-----------------<br>
Physicist - Meteorologist, M.Sc.<br>
Ph.D. Candidate, Polytechnic School of Paris, France<br>
Laboratory of Dynamic Meteorology (LMD)<br>
Research Associate, National Observatory of Athens<br>
Tel. : <a href="tel:%28%2B33%299%2081%2094%2022%2012" value="+33981942212">(+33)9 81 94 22 12</a><br>
Mobile: <a href="tel:%28%2B33%29%20066%20030%200147" value="+33660300147">(+33) 066 030 0147</a><br>
<a href="tel:%28%2B30%29%20697%2004%2020%20242" value="+306970420242">(+30) 697 04 20 242</a><br>
---------------<br>
Weather charts:<br>
<a href="http://www.meteo.gr" rel="noreferrer" target="_blank">http://www.meteo.gr</a><br>
<a href="http://www.meteo.gr/meteomaps/" rel="noreferrer" target="_blank">http://www.meteo.gr/meteomaps/</a><br>
<br>
<br>
<br>
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</blockquote></div><br></div>