# [SciPy-User] Obtaining contour data

Slavin, Jonathan jslavin at cfa.harvard.edu
Mon Oct 16 13:39:36 EDT 2017

```Ashwin,

I have found that the scikit image routine find_contours is easier to work
with than extracting the data from the ContourSet object as in the cited
stackoverflow example.  If you do something like

from skimage.measure import find_contours
cs = find_contours(array, values)

(where values are the levels you want for your contours and array is the
grid of values) then you get back a list of contour lines.  For each
contour you have a Nx2 array of effective indices into the array.  You can
convert to your lat-long grid by multiplying by the appropriate scales.
skimage also has a nice routine called grid_points_in_poly which will
return a boolean array that is True for all points of the input array that
are inside the polygon to which you can use one of the contours as an input.

Regards,
Jon

On Mon, Oct 16, 2017 at 10:31 AM, <scipy-user-request at python.org> wrote:

>
> Date: Mon, 16 Oct 2017 19:01:27 +0530
> From: "ashwin .D" <winash12 at gmail.com>
> To: scipy-user at python.org
> Subject: [SciPy-User] Winds/sfc_trough.html
> <http://www.indiana.edu/%7Egeog109/topics/10_Forces&Winds/sfc_trough.html>
> .
> > The data is plotted on a two dimensional latitude longitude grid and then
> > the height contours are calculated. I am looking to obtain the
> coordinates
> > of the contours(shown in red) in terms of latitude and longitude so that
> I
> > can use that information  to calculate the curvature of the contour
> points
> > using a least squares method. Is it possible to do this in Scipy ? The
> > curvature of the earth is itself irrelevant in this case and it can be
> > assumed to be flat.
> >
> > Regards,
> > Ashwin.
> >
> > _______________________________________________
> > SciPy-User mailing list
> > SciPy-User at python.org
> > https://mail.python.org/mailman/listinfo/scipy-user
>
--
________________________________________________________
Jonathan D. Slavin                 Harvard-Smithsonian CfA
jslavin at cfa.harvard.edu       60 Garden Street, MS 83
phone: (617) 496-7981       Cambridge, MA 02138-1516
cell: (781) 363-0035             USA
________________________________________________________
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