Matlab contourf() to plot data on a global map

Question

I have been using Matlab 2011b and contourf/contourfm to plot 2D data on a map of North America. I started from the help page for contourfm on the mathworks website, and it works great if you use their default data called "geoid" and reference vector "geoidrefvec."

Here is some simple code that works with the preset data:

figure
axesm('MapProjection','lambert','maplo',[-175 -45],'mapla',[10 75]);
framem; gridm; axis off; tightmap

load geoid
%geoidrefvec=[1 90 0];

load 'TECvars.mat'
%contourfm(ITEC, geoidrefvec, -120:20:100, 'LineStyle', 'none');
contourfm(geoid, geoidrefvec, -120:20:100, 'LineStyle', 'none');

coast = load('coast');
geoshow(coast.lat, coast.long, 'Color', 'black')
whitebg('w')
title(sprintf('Total Electron Content Units x 10^1^6 m^-^2'),'Fontsize',14,'Color','black')
%axis([-3    -1   0    1.0]);
contourcbar

The problem arises when I try to use my data. I am quite sure the reference vector determines where the data should be plotted on the globe but I was not able to find any documentation about how this vector works or how to create one to work with different data.

Here is a .mat file with my data. ITEC is the matrix of values to be plotted. Information about the position of the grid relative to the earth can be found in the cell array called RT but the basic idea is. ITEC(1,1) refers to Lat=11 Long=-180 and ITEC(58,39) refers to Lat = 72.5 Long = -53 with evenly spaced data.

Does anyone know how the reference vector defines where the data is placed on the map? Or perhaps there is another way to accomplish this? Thanks in advance!

Answer 1

OK. So I figured it out. I realized that, given that there are only three dimensions in the vector, the degrees between latitude data must be the same as the degrees between longitude data. That is, the spacing between each horizontal data point must be the same as the spacing between each vertical point. For instance, 1 degree.

The first value in the reference vector is the distance (in degrees) between each data point (I think...this works in my case), and the two second values in the vector are the minimum latitude and minimum longitude respectively.

In my case the data was equally spaced in each direction, but not the same spacing vertically and horizontally. I simply interpolated the data to a 1x1 grid density and set the first value in the vector to 1.

Hopefully this will help someone with the same problem.

Quick question though, since I answered my own question do I get the bounty? I'd hate to loose 50 'valuable' reputation points haha