Plot data on sphere/world map

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Heiko
Heiko on 17 Apr 2013
Hello all!
I have a dense set of 2D points on a sphere (theta,phi). For each of those points, I have an observation (obs). I can convert the points to 3D Cartesian points and then do a scatter plot of the observations
scatter3(x,y,z,1,obs);
This generates an image which looks like this. http://herrstrathmann.de/files/world.png
What I would like to have an interpolated version of the data and a surface plot. For this I somehow need to interpolate the 2D coordinates into a grid. The current scatter plot looks a bit ugly. I have tried the following code which however creates artefacts on the edges. After all, the sphere is periodic. How can I interpolate nicely?
p=linspace(min(theta)+1, max(theta)-1);
q=linspace(min(phi)+1, max(phi)-1);
[p,q]=meshgrid(p,q);
obs_interp=griddata(theta,phi,obs,p,q);
Once I have the inteprolated data, how do I plot it onto the surface of the sphere in a nice way?
On top of all that, I would like to plot the world map. Is that somehow possible? I can align it myself once I know how it basically works
Many thanks for your help! Heiko

Answers (1)

Angus
Angus on 11 Jun 2013
Im not sure if you need to interpolate at all ... you have a 2d matrix of data with associated vectors for phi and theta? Then you should be able to display it as is using the mapping toolbox.
Lets say you had
theta = [-179:180];
phi = [-89:90];
obs % 360x180 2d array of data
[lat_grid,lon_grid] = meshgrid(theta,phi); % should both be 360x180 to match data
load coast % loads lat and long variables that define the coastline
worldmap('World') % also try axesm as it gives more options
geoshow(lat,long) % draw the coastlines
pcolorm(lat_grid,lon_grid,obs) % a pseudo-color plot of obs data on the projected grid
Hope that helps (alternately, hope you found a solution already)
Cheers, Angus

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