How to change land data to NaN?

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eevee il 27 Ott 2014

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Risposto: Chad Greene il 5 Dic 2014

Hi,

I have plotted a bathymetry and now I'm given coastline and some islands files where I need to use them to define where the land is and then turn the land data to NaN.

How should I do that?

Thanks, Eve

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Geoff Hayes il 29 Ott 2014

Eve - how do you (currently) calculate the volume? What information do you use for that?

eevee il 30 Ott 2014

Hi Geoff,

I use:

dx*dy*zi(~isnan(zi))

However, my zi includes both land and sea data. So now, I need to remove the land data before I could calculate the volume of bathymetry. I don't know how to tell matlab that my land data are those that falls below the coastline (please see image below)

Thanks,

Eve

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Kelly Kearney il 27 Ott 2014

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The inpolygon function will do most of the work. Depending on the scale of your region and the format of the coastlines, you may need to close off polygons, reverse order of vertices, and upsample polygons in order to get the best results; the Mapping Toolbox has several functions ( flatearthpoly, interpm, ispolycw, poly2cw) to help with that.

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eevee il 31 Ott 2014

sub14n11test.m

Hi Kelly,

sorry I just realized I forgot to attach my script. :)

Kelly Kearney il 31 Ott 2014

Apri in MATLAB Online

Can you upload the coastline file? The answer will depend on whether it contains just the visible line segments you plotted above, or fully-closed polygons. Assuming it's the latter, your code to mask the land points will look something like:

isin = inpolygon(xi, yi, xcoast, ycoast);
zi_diff(isin) = NaN;

But you may need to do some processing of xcoast and ycoast to convert them to closed, clockwise polygons.

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Chad Greene il 5 Dic 2014

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Another solution is the landmask function on File Exchange.

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