# Re: Concave boundary fill problem in contour of transect

From: David Brown <dbrown_at_nyahnyahspammersnyahnyah>
Date: Wed Apr 04 2012 - 16:59:46 MDT

Hi Carmen,

This is an interesting problem (triangular-mesh in the horizontal vs layers in the vertical) that we do not have much experience with. We definitely would like to find a solution, but I don't have a ready answer. Perhaps someone on the list has a suggestion.
-dave

On Mar 30, 2012, at 9:11 AM, Carmen St. Jean wrote:

> Hello everyone,
>
> I'm attempting to use PyNGL create a transect of water temperatures in
> the Northern Gulf of Mexico using a NetCDF file of NOAA/NOS' Northern
> Gulf of Mexico Operational Forecast System (NGOFS). However, the
> contour plot seems to be bleeding into the concave boundary areas of
> the mesh and I'm not sure how to prevent this.
>
> My strategy has been:
> 1. Given two lat/lon coordinates, draw a transect line between them.
> 2. For each sigma layer, interpolate the water temperature at the
> points on the transect line (using natgrid).
> 3. For each sigma layer, interpolate the depths at the points on the
> transect line (using natgrid).
> 4. Plot the interpolated water temperatures as a contour with the
> interpolated depths as the y-axis and the lat/lon of the points on the
> transect line as the x-axis.
>
> (Unfortunately, natgrid takes an extremely long time to run because
> the NGOFS grid is a triangular mesh of over 90,000 nodes. So before
> step 1, I'm drawing a bounding box around the transect line and
> subsetting the data from the NGOFS NetCDF file to only the nodes the
> fall within that bounding box.)
>
> I've played around with various resources, but nothing seems to stop
> the contour from filling in areas erroneously when I try to plot the
> temperature by depth (see attachment "ngofs-transect-z.png"). I
> plotted the interpolated water temperatures against sigma layer rather
> than z (see attachment "ngofs-transect-siglay.png") and showed it to
> an oceanographer familiar with NGOFS. He said the plot seemed to be
> correct, so I'm confident the interpolation is working correctly.
>
> Are there any resources I should be setting to fix this problem? Or
> perhaps is there an easier method to creating a transect that I have
> overlooked?
>
> Here is the file I'm using for input:
> http://opendap.co-ops.nos.noaa.gov/netcdf/ngofs/201203/nos.ngofs.fields.nowcast.20120322.t03z.nc
>
> Thank you,
>
> Carmen
> <ngofs-transect.py><ngofs-transect-siglay.png><ngofs-transect-z.png>_______________________________________________
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Received on Wed Apr 4 16:59:55 2012

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