In NCL Version 6.2.0, new resources were introduced that significantly speed up the drawing of ICON data done with filled polygons. See examples #2, #3, and #5 below for more information and sample scripts.
Visualizing ICON model data
The variables "clon" and "clat" on the file are used to indicate the center lat/lon locations of the triangles, so we can overlay this data on a map.
Because these arrays are all one-dimensional, internally NCL is using a triangular mesh algorithm to create the contours.
Note that this example is a bit of an overkill, because the contout plot is being drawn and then completely covered by the filled triangles. It is necessary to create and draw the contour plot so we get tickmarks and a labelbar. We also use the contour plot to retrieve what levels and colors to use for the filled triangles.
The next example shows how to create and draw the filled triangles using just a map plot.
Similar to the "icon_faster_2.ncl" script above, you can create a faster version of this script using new resources gsSegments and gsColors, which are available in NCL Version 6.2.0. See the "icon_faster_3.ncl" script. The "icon_3.ncl" script took about 1.64 CPU seconds on a Mac, and "icon_faster_30.ncl" took about 0.33 CPU seconds.
The second frame draws filled triangles over a map, this time using gsn_add_polygon to attach the filled triangles. Note that it takes a long time to draw this second frame, because there are thousands of individual triangles being filled. Also, some triangles "wrap" around the globe, so these have to be fixed.
Similar to the "icon_faster_2.ncl" script above, you can create a faster version of this script using new resources gsSegments and gsColors, which are available in NCL Version 6.2.0. See the "icon_faster_5.ncl" script. The "icon_5.ncl" script took about 38 CPU seconds on a Mac, and "icon_faster_5.ncl" took about 0.55 CPU seconds.
The overlay procedure is used to overlay the two high-resolution fields onto the global field. cnFillDrawOrder and cnLineDrawOrder are set to "PostDraw" for the overlaid plots to make sure they get drawn on top of all the elements from the global field.
This example was contributed by Daniel Reinert of Deutscher Wetterdienst (the German Meteorological Service).