<div dir="ltr"><div class="gmail_default" style="font-size:small"><div class="gmail_default">Dear NCL talk,</div><div class="gmail_default"><br></div><div class="gmail_default">Recently, I found an issue on the generation of grid meshes using a prescribed map projection information. The detail of the problem is as follows:</div><div class="gmail_default"><br></div><div class="gmail_default">When I read HRRR grib files to generate plots, I get lat,lon information form these two NCL-provided variables: </div><div class="gmail_default">mylat = t_file-><b>gridlat_0</b><br></div><div class="gmail_default" style="font-size:12.800000190734863px">mylon = t_file-><b>gridlon_0</b></div><div class="gmail_default"><br></div><div class="gmail_default">The variable summary is as follows:<br></div><div class="gmail_default"><div class="gmail_default"><i><br></i></div><div class="gmail_default"><i>Variable: mylat</i></div><div class="gmail_default"><i>Type: float</i></div><div class="gmail_default"><i>Total Size: 7620564 bytes</i></div><div class="gmail_default"><i> 1905141 values</i></div><div class="gmail_default"><i>Number of Dimensions: 2</i></div><div class="gmail_default"><i>Dimensions and sizes: [ygrid_0 | 1059] x [xgrid_0 | 1799]</i></div><div class="gmail_default"><i>Coordinates:</i></div><div class="gmail_default"><i>Number Of Attributes: 11</i></div><div class="gmail_default"><i> corners : ( 21.13812, 21.14055, 47.84219, 47.83862 )</i></div><div class="gmail_default"><i> long_name : latitude</i></div><div class="gmail_default"><i> grid_type : Lambert Conformal (secant, tangent, conical or bipolar)</i></div><div class="gmail_default"><i> units : degrees_north</i></div><div class="gmail_default"><i> Latin2 : 38.5</i></div><div class="gmail_default"><i> Latin1 : 38.5</i></div><div class="gmail_default"><i> Dy : 3</i></div><div class="gmail_default"><i> Dx : 3</i></div><div class="gmail_default"><i> Lov : 262.5</i></div><div class="gmail_default"><i> Lo1 : 237.2805</i></div><div class="gmail_default"><i> La1 : 21.13812</i></div></div><div class="gmail_default"><br></div><div class="gmail_default">As show above, the variable contains the prescribed HRRR model map projection information. I believe this information is used by NCL internally to generate lat,lon values. </div><div class="gmail_default"><br></div><div class="gmail_default">The problem is that these re-generated lat,lon values are not consistent with the original HRRR model lat,lon values. </div><div class="gmail_default">I printed out lat,lon values for the botten-left corner, center and its surrounding four points, and the upper-right corner as below:</div><div class="gmail_default"><br></div><div class="gmail_default"><b style="background-color:rgb(255,255,0)">For original HRRR lat,lon values:</b></div><div class="gmail_default"><div class="gmail_default">(1,1): 21.13812, -122.7195</div><div class="gmail_default">c_left: 38.49999,-97.53448</div><div class="gmail_default">center: 38.5, -97.5</div><div class="gmail_default">c_right: 38.49999,-97.46552</div><div class="gmail_default"><br></div><div class="gmail_default">c_down: 38.47303, -97.5</div><div class="gmail_default">center: 38.5, -97.5</div><div class="gmail_default">c_up: 38.52699, -97.5</div><div class="gmail_default"><br></div><div class="gmail_default">(nx,ny): 47.84364, -60.90137</div></div><div class="gmail_default"><br></div><div class="gmail_default"><b style="background-color:rgb(255,255,0)">For NCL re-genrated lat,lon values based on prescribed HRRR map projection info:</b></div><div class="gmail_default"><div class="gmail_default">(1,1) : 21.13812, -122.7195</div><div class="gmail_default"><br></div><div class="gmail_default">c_left: 38.49724, -97.54045</div><div class="gmail_default">center: 38.49725, -97.50597</div><div class="gmail_default">c_right: 38.49724, -97.4715</div><div class="gmail_default"><br></div><div class="gmail_default">c_down: 38.47027, -97.50597</div><div class="gmail_default">center: 38.49725, -97.50597</div><div class="gmail_default">c_up: 38.52422, -97.50598</div><div class="gmail_default"><br></div><div class="gmail_default">(nx,ny): 47.84219, -60.91719</div></div><div class="gmail_default"><br></div><div class="gmail_default">You can see that for the original HRRR lat,lon mesh, the center is exactly (38.5, -97.5) as defined by the map projection info, while the NCL re-gererated lat,lon mesh is <b>not</b> so. Except the bottom-left point, all other lat,lon values from NCL shift from the original HRRR values.</div><div class="gmail_default"><br></div><div class="gmail_default">This NCL behavior caused a slight shift in my physical variable plots (based on GRIB files) as compared to original ones. Could you advise me how NCL generate these lat,lon values? Can you help me examine and fix this issue? </div><div class="gmail_default"><br></div><div class="gmail_default">Let me know if you need more information.</div><div class="gmail_default"><br></div><div class="gmail_default">Thanks,</div><div class="gmail_default"><br></div><div class="gmail_default">Guoqing</div><div><br></div></div><div class="gmail_default" style="font-size:small"><br></div><div class="gmail_default" style="font-size:small"><br></div><div><div class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr">--</div><div>Guoqing Ge, PhD</div><div>CIRES Research Scientist<br></div><div>at NOAA/ESRL/GSD (Rm 2B502)<span><br></span></div><div dir="ltr"><span style="color:rgb(0,0,0)">325 Broadway, Boulder, CO 80305</span></div><div dir="ltr"><font color="#000000">(303)497-4163<br></font><div><span style="color:rgb(0,0,0)">&</span></div><div><span style="color:rgb(0,0,0)">Thursdays at</span></div><div><font color="#000000">Developmental</font><span style="color:rgb(0,0,0)"> Testbed Center (FL3-1039)</span></div><div>3450 Mitchell Ln, Boulder, CO 80301<span style="color:rgb(0,0,0)"><br></span></div><div>(303)497-8445</div><div><span style="color:rgb(0,0,0)"><br></span></div><div><span style="color:rgb(0,0,0)"><br></span></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div>
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