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- Preferred method:
- Here we follow a procedure developed by Oksana Guba where we draw the PNG image on top of a background image of a cubed-sphere grid. This allows one to have better control over the refined region’s boundaries and avoid notches and other types of glitches in the transition region.
- If the fine region will be (for example) NE120 (¼ degree), make a uniform NE60.g file (exactly half the resolution of the fine region).
- This can be done via; SQuadGen --resolution 60 --refine_level 0 --output NE60.g
- Create a lat/lon plot of this NE60 mesh, without any borders or axis, and convert to a PNG file with an aspect ratio of 2. The final resolution should be something like 2048x4096.
You can convert SQuadGen output to PNG using gridplot.ncl in the SQuadGEN test directory.
- Here's an example of the kind of file you want:
- This PNG file will be used as a background image in Photoshop or GIMP. The PNG of the refined region is then drawn on top of this image (in a separate layer).
- Create a PNG of the same dimensions as the file above which is transparent where the coarse grid is used and black where refinement is needed.
- For best results, create a PNG that is transparent (so you can see the NE60 grid behind it) and then fill in, in white, the elements that should be refined to NE120.
- For best results the border should follow the grid lines, or go at a 45 degree angle (i.e. over 1 element, then down 1 element, and repeat).
- Save the new PNG (without the background image). Here we assume the file is called newmesh.png
- An example of the PNG file:
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- Use SQuadGen to create the refined grid:
./SQuadGen --refine_file newmesh.png --refine_level 3 --refine_type LOWCONN \
--resolution 16 --smooth_type SPRING --smooth_dist 3 --smooth_iter 20 \
--output newmesh.g - Plot the final grid and make sure it does not have any highly deformed elements.
- Please note: If you use the LOWCONN option for --refine_type, try to avoid six elements around one point by editing the white parts of the PNG. Six elements around a point is unavoidable with the CUBIT option.
- The mesh generated by the PNG file above is:
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