On 09/13/2011 06:36 AM, Leidner, Mark wrote: > > Dear Python/Matplotlib/Ogr Users: > > We are recent converts to Python, and are having trouble with some of > its functionalities. > We'd like to submit our case for your consideration in hopes to get some > educated help on the subject. > > The problem: > When trying to use contour collections generated by contourf, the > resulting shapefile contains overly simplified contours which poorly > approximate the underlying field. > > To reproduce the problem, we wrote a python script that specifies a 2-d > analytical shape. This shape has small noise perturbations added, in > order to simulate natural geophysical fields (wind speed, for example).
Your illustration seems horrendously complex. Can you distill it down to a simplest-possible case? Doing so might help you figure out where the problem is. I don't think it has anything to do with path simplification, because that occurs when the path is rendered. If I understand correctly, what mpl is plotting directly from your data is fine; you are running into surprises with the shapefile that you are generating from what mpl is using for its plotting. So, the problem would seem to be in the generation of the shapefile, not in mpl. Eric > . > The shape is being sliced by contourf command, and the resulting > collection is being plotted as a PDF file (PostScript) and converted to > an output Shapefile using OGR module. > > We also wrote several functions, defined inside the script, that take > care of unpacking and exporting the contour collections as polygon or > multipolygon shapefile entities thru OGR shapefile methods. > > Two zoomed in views are attached (screenshot_* attachments): (1) a > portion of the PDF figure, and (2) a visualization of the shapefile data > for the same area. The PDF figure shows a contour line with fine scale > structure (the fine structures are the noise we added) while a lack of > fine structure is seen in the output shapefile. The PDF plot is what we > expect. The output shapefile geometry is very different from what we > would expect. > > We can't understand how a call to contourf can produce a plot that looks > right AND shapefile data (taken from contourf's collections) that appear > to grossly simplify the geometry. We expect that both the plot and the > shapefile come from the same contourf function results, yet look totally > different. > > We'd like to ask whether anyone else encountered limitations regarding > the complexity of shapefiles written out by python? > Is this a possible problem with matplotlib.pyplot.contourf.collections > method? > > We would appreciate your help very much! > Test script and the resulting shapefile data set are attached. > > Thank you! > > ------------------------------------------------------------------------ > > ------------------------------------------------------------------------ > > S. Mark Leidner > Staff Scientist/Oklahoma Business Development > Atmospheric and Environmental Research, Inc. > 350 David L. Boren Blvd, Suite 1535 > Norman, OK 73072-7264 USA > ph: +1 405 325-1137 > cell: +1 781 354-5969 > > > Sergey Vinogradov, Ph.D., Staff Scientist > Atmospheric and Environmental Research, Inc. > 131 Hartwell Ave., Lexington, MA 02421, USA > Phone: 1-781-761-2256 ser...@aer.com > Fax: 1-781-761-2299 http://www.aer.com > Web page :: http://ocean.mit.edu/~svinogra > > > > > > > > ------------------------------------------------------------------------------ > BlackBerry® DevCon Americas, Oct. 18-20, San Francisco, CA > Learn about the latest advances in developing for the > BlackBerry® mobile platform with sessions, labs& more. > See new tools and technologies. Register for BlackBerry® DevCon today! > http://p.sf.net/sfu/rim-devcon-copy1 > > > > _______________________________________________ > Matplotlib-users mailing list > Matplotlib-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/matplotlib-users ------------------------------------------------------------------------------ BlackBerry® DevCon Americas, Oct. 18-20, San Francisco, CA Learn about the latest advances in developing for the BlackBerry® mobile platform with sessions, labs & more. See new tools and technologies. Register for BlackBerry® DevCon today! http://p.sf.net/sfu/rim-devcon-copy1 _______________________________________________ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
