Contours and shapefiles

Hi,

I am trying to plot contours over a map of US climate divisions. I imported a climate division shapefile, then found the centroid of each division. Next, I used the meshgrid and triscatteredInterp functions to interpolate the data on a grid. Finally I used the contour function to get isolines.

Once I plotted my isolines over my USA climate division map, I noticed that the contours go outside the US (and outside my centroids used in the meshgrid, etc. calculations). Is there a way to "contain" the centroids to the boundaries of the USA?

Thanks! Deb

Answer 1

[Kelly Kearney]

Not quite sure whether your trying to contain individual points, or the contour lines themselves, and whether you're trying to mask with a polygon (the US coastlines) or just a bounding box. A few functions that might help:

 help inpolygon
 help polybool
 help maptriml
 help maptrimp

If none of these seem to do the trick, perhaps a little more detail on your data could be helpful.

EDIT: an example. I've used the contourcs function to extract isolines; I assume you already have this data, but if you want to run my example, download that from the FEX.

 % Load coastlines (replace with your coastlines)

 latlim = [23 50];
 lonlim = [-127 -65];

 Usa = shaperead('landareas', 'usegeo', true, 'bounding', [lonlim' latlim']);
 [latusa, lonusa] = maptrimp(Usa(1).Lat, Usa(1).Lon, latlim, lonlim);

 % Create isolines (replace with your isolines)

 n = 50;
 xdata = linspace(lonlim(1), lonlim(2), n);
 ydata = linspace(latlim(1), latlim(2), n);
 zdata = peaks(n);
 S = contourcs(xdata, ydata, zdata); % FEX

 % Trim to coastlines

 [xc, yc] = deal(cell(length(S),1));
 for ii = 1:length(S)
    [xc{ii}, yc{ii}] = polybool('&', S(ii).X, S(ii).Y, lonusa, latusa);
 end

 % Plot

 figure; axes; hold on;
 plot(lonusa, latusa, 'k');
 cnew = [xc yc]';
 hn = plot(cnew{:}, 'r');
 set(hn, 'color', 'b');

[Debra]

Thank you for getting back to me.

I am trying to contain the contour lines themselves. I want to use US coastlines as the boundary.

[Kelly Kearney]

Okay, I've added an example to demonstrate using polybool to trim isolines to a coastline.

[elvis asong ZILEFAC]

error: Improper index matrix reference.

Hi Kelly,

I have a similar problem and your answer does it all. However, I receive the above error just after running your code.

Asong.