All,
We try to generate contour polygons from an unstructured triangular grid
stored in a netcdf file:
import netCDF4
import matplotlib.tri as tri
# read data
var = netCDF4.Dataset('filename.cdf').variables
x = var['x'][:]
y = var['y'][:]
elems = var['element'][:,:]-1
data = var['attrname'][:]
# create triangulation
triang = tri.Triangulation(x, y, triangles=elems)
# generate contour polygons
levels = numpy.linspace(0, maxlevel, num=numlevels)
contour = plt.tricontourf(triang, data, levels=levels)
# extract geometries
for coll in contour.collections:
# handle all geometries for one level
for p in coll.get_paths():
polys = p.to_polygons()
...
At this point we assume, that polys[0] is a linear ring to be interpreted as
a polygon exterior and polys[1:] are the corresponding interiors for
polys[0].
Here are our questions:
Is this assumption correct?
Is there any detailed documentation describing the structure of the returned
geometries?
Are the linear rings supposed to be correctly oriented (area > 0 for
exteriors and area < 0 for the interiors)?
Thanks!
Regards Hartmut
---------------
http://boost-spirit.com
http://stellar.cct.lsu.edu
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