Patrick Marsh wrote:
> Hi Jeff (and others):
>
> Sorry for the misunderstanding. After your second email the first
> makes more sense.
>
> However, I still cannot figure out how to extract the lat,lon pairs
> from the LineCollection object. Searching on the web and based on
> Scott's suggestion from another email, I see that in the past you
> could use a get_vertex() option. However it appears to have been
> discontinued in mpl v 0.98.1. <http://0.98.1.>
Scott: Sorry, you're right - it's far from obvious how to get the x,y
coordinates pairs out of a LineCollection. Each contour has a
'collections' attribute that is a LineCollections object. The
get_paths() method of the LineCollections object returns a list of a
matplotlib.path.Path objects, each of which has a 'vertices' attribute.
So, something like this works for me in 0.98:
for xy in CS.collections[0].get_paths(): # get the paths for the first
contour
for xy in xy.vertices: # iterate over the Path objects
# xy[0],xy[1] are the x,y coordinates
# these are the lon,lat coords (map is the Basemap instance)
lon, lat = map(xy[0],xy[1],inverse=True)
>
> I'm a relative newcomer to Python (less than 6 months) and even
> greener when it comes to the inner workings of matplotlib. I'm sure
> I'm going to kick myself when this is figured out...
>
> -Patrick
No worries - don't kick yourself. Although matplotlib is quite easy to
use in general, the 'inner workings' take a while to grok.
-Jeff
>
>
> On Sat, Aug 2, 2008 at 7:33 PM, Jeff Whitaker <[EMAIL PROTECTED]
> <mailto:[EMAIL PROTECTED]>> wrote:
>
> Patrick Marsh wrote:
>
> Thanks for the quick reply.
>
> I may not have been totally clear on what I'm trying to save
> (or I totally misunderstood what you were trying to say -
> which is certainly possible).
>
> I'm not wanting to save the lat, lon pairs from the map
> projection. I'm trying to save the lat, lon pairs of the
> contour. Using my original example, if I'm plotting winds
> every 5 m/s, I'm wanting to pull off the lat, lon pairs for
> the 5 m/s contours.
>
>
> Patrick: I know - that's what I was trying to explain. You can
> get the x,y coordinates of the *contours* from the collections
> attribute of the ContourSet object returned by contour. Then you
> convert those x,y values back to lon,lat values using the Basemap
> instance.
>
> -Jeff
>
>
> I'll check out the website and see if I find anything there.
>
> -Patrick
>
>
>
> On Sat, Aug 2, 2008 at 6:13 PM, Jeff Whitaker
> <[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>
> <mailto:[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>>> wrote:
>
> Patrick Marsh wrote:
>
> Hi Everyone,
>
> First email here...
>
> I am plotting meteorological data using matplotlib and
> basemap - and can do this just fine. However, I would
> like to backout the coordinates being used for the
> contours that are plotted.
>
> For example, if I were to contour windspeed every 5 m/s
> and plot this (which I can do just fine), I would
> like to
> save a copy of the lat, lon pairs as a text file.
> However, I cannot for the life of me figure out
> how to do
> this. I have a feeling it is pretty simple and I'm
> just
> over looking something that can do this. Any help
> would
> be appreciated.
>
> Thanks,
>
> -Patrick Marsh
> Graduate Student
> School of Meteorology
> University of Oklahoma
>
>
> Patrick: contour and contourf return a ContourSet object.
> ContourSet.collections is a matplotlib LineCollection (for
> contour) or a PolyCollection (for contourf). You can
> retrieve
> the x,y (map projection) coordinates from these, and
> transfer
> them back to lat/lon coordinates using the Basemap
> instance via
>
> lons,lats = map(x,y,inverse=True) # map is a Basemap
> instance.
>
> See
>
> http://matplotlib.sourceforge.net/doc/html/api/collections_api.html
> for more info on matplotlib collection objects.
>
> HTH,
> -Jeff
>
>
>
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> -- Jeffrey S. Whitaker Phone : (303)497-6313
> NOAA/OAR/CDC R/PSD1 FAX : (303)497-6449
> 325 Broadway Boulder, CO, USA 80305-3328
>
>
>
>
>
> --
> Jeffrey S. Whitaker Phone : (303)497-6313
> NOAA/OAR/CDC R/PSD1 FAX : (303)497-6449
> 325 Broadway Boulder, CO, USA 80305-3328
>
>
--
Jeffrey S. Whitaker Phone : (303)497-6313
NOAA/OAR/CDC R/PSD1 FAX : (303)497-6449
325 Broadway Boulder, CO, USA 80305-3328
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