MATLAB: Is there a fix for a bug in the gshhs function from the MATLAB mapping tool box? Faulty section of coast off South America.

Question

I am creating maps of Antarctica and the surrounding Southern Ocean to show ocean chlorophyll content, so using a polar viewpoint with a stereo map projection and using the current version of MATLAB, MATLAB_R2014a. When using the gshhs function from MATLAB's mapping toolbox to create the coastlines, myself and my supervisor have found a visible fault along South America's East coast and a section of the surrounding waters. This occurs with both the course and low level resolution files, we are yet to try the higher resolutions (they obviously take longer processing times).

Has anyone else come across this before and/or does anyone have a solution to this?

An example of the maps we are producing with the specified problems is attached and the code we used to create it is given below. Any help would be much appreciated.

close all; clear all;
S = netcdf.open('S20060012006031.L3m_MO_SO_Chl_9km.Johnson_SO_Chl.nc4', 'NC_NOWRITE');
% for i = 0:10
%     netcdf.inqVar(S,i)
% end
chl = netcdf.getVar(S,0);
lat = netcdf.getVar(S,1);
lon = netcdf.getVar(S,2);
netcdf.close(S);
z = find(lon<0); lon(z) = lon(z)+360;
lon = lon';
for i = 1:720
clon(i,:) = lon;
end
for i = 1:4320
clat(:,i) = lat;
end
z = find(chl <0); chl(z) = NaN; clear z;
chl = double(chl');
% pcolor(lon, lat, log10(chl)); shading flat;
world = gshhs('gshhs_c.b');
h = figure('Color','white')
set(h,'papertype','tabloid')
set(h,'paperposition',[0 0 10 5]); %Gives exactly 2000 x 1000 pixel image
set(h,'InvertHardCopy','off'); %keep set background colors when printing to file
a = axesm('MapProjection','stereo','MapLatLimit',[-90 -30],'MapLonLimit',[0 360],'Frame','on','Grid','off','GLineStyle','-','GLineWidth',1,'MLineLocation',2,'PLineLocation',1,'MeridianLabel','on','ParallelLabel','on','PLabelLocation',[-80:10:-30],'MLabelLocation',[0:30:360],'FontSize',16,'FontWeight','Bold','LabelRotation','on')
set( gca, 'Visible', 'off' ) ;
geoshow([world.Lat], [world.Lon], 'DisplayType','polygon','FaceColor',[0.5 0.5 0.5])
hold on
pcolorm(lat, lon, log10(chl));

Thank you in advance!

Answer 1

All of Matlab's built-in coastlines are pretty lousy, but here's a fix:

Delete world = gshhs('gshhs_c.b'); and delete the geoshow([world.Lat], [world.Lon], 'DisplayType','polygon','FaceColor',[0.5 0.5 0.5]) lines. Instead, at the very end of everything, try this:

load coast; 
patchm(lat,long,.5*[1 1 1])

I say do this at the very end because load coast loads an array named lat and we don't want to confuse it with the lat matrix you already have.

Also, two tricks that are unrelated to your question: First, I see a seam along the meridian where your chlorophyll data meets itself. Overlap that data by repeating a column of data as described here. And second, when you create your colormap, it's a nice habit to use jet(256) instead of the default jet, which only creates 64 colors. The difference is an aesthetic preference of mine and is not integral to the data display, but the smooth color gradient helps bring Matlab graphics into the 21st century.