How can you plot lines of latitude and longitude on a globe without using the mapping toolbox ?

I have a function that displays the countries of the world on a global plot and I need to know how to plot lines of lat and lon in even increments of 10 degrees onto this global plot without using the geoshow command found in the mapping toolbox.

[KSSV]

You need to change the long and lat data from degrees to spherical coordinates and then use surf...

[Rik]

You could even use plot3 to generate the wire mesh.

As to examples: spherical coordinates work similar to polar coordinates (x=r*sin(theta),y=r*cos(theta)), so you can expand that to 3D without too much trouble.

[per isakson]

Maybe it's worth looking in the File Exchange. Try lon lat plot.

Answer 1

[Chad Greene]

Update - as for R2018b, the geoplot function in MATLAB can be used as a way to plot latitude and longitude data on a 2-D global map.

*******

You can do this easily with the standard matlab function sph2cart. Treat the lines of latitude and longitude separately like this:

R = 6371; % earth radius in km
latspacing = 10; 
lonspacing = 20; 

% lines of longitude: 
[lon1,lat1] = meshgrid(-180:lonspacing:180,linspace(-90,90,300)); 
[x1,y1,z1] = sph2cart(lon1*pi/180,lat1*pi/180,R); 
plot3(x1,y1,z1,'-','color',0.5*[1 1 1])

hold on

% lines of latitude: 
[lat2,lon2] = meshgrid(-90:latspacing:90,linspace(-180,180,300)); 
[x2,y2,z2] = sph2cart(lon2*pi/180,lat2*pi/180,R); 
plot3(x2,y2,z2,'-','color',0.5*[1 1 1])

axis equal tight off

And since you can see all the way through the globe, perhaps you want to put an opaque sphere inside the globe. Do that like this. I'm making the sphere 0.99 times the size of the Earth just to make sure it doesn't overlap the lines of lat and lon:

[X,Y,Z] = sphere(100); 
surf(X*R*.99,Y*R*.99,Z*R*.99,'facecolor','w','edgecolor','none')

For a little context, I'll also convert national borders to cartesian coordinates in the same way. You'll need the data from my borders function for this part:

C = load('borderdata.mat');
for k = 1:246
   [xtmp,ytmp,ztmp] = sph2cart(deg2rad(C.lon{k}),deg2rad(C.lat{k}),R);
   plot3(xtmp,ytmp,ztmp,'k') 
end

[Ni Wi]

Is there any way how to easily apply elevation data to the grid?

[Chad Greene]

If you have the Mapping Toolbox, try

load topo

Then convert to cartesian coordinates and plot with surf. If you don't have the Mapping Toolbox you'll need to find the topographic data somewhere out on the internet.

[Margareta]

Hi Chad,

that's a very neat solution - thank you very much!

I have a related question - what if I want to "hide" the latitude and longitude of the hemisphere facing the viewer, and only plot the opposite hemisphere - with the borders of countries? I'm sort of trying to obtain a view of countries and continents that someone sitting at the center of the Earth, facing the same direction as the viewer looking at the figure, would see if the planet suddenly became transparent :-)

Looking forward to ideas and tips from all you Matlab gurus out there! /Maggie

[Chad Greene]

Yikes, I can't figure out a great way to show it, but here's something. Basically NaN out whichever half the globe you don't want to see, then set the viewing angle.

R = 6371; % earth radius in km
latspacing = 10; 
lonspacing = 20; 

% lines of longitude: 
[lon1,lat1] = meshgrid(-180:lonspacing:180,linspace(-90,90,300)); 
[x1,y1,z1] = sph2cart(lon1*pi/180,lat1*pi/180,R); 

z1(lon1<0) = nan; 
plot3(x1,y1,z1,'-','color',0.5*[1 1 1])

hold on

% lines of latitude: 
[lat2,lon2] = meshgrid(-90:latspacing:90,linspace(-180,180,300)); 
[x2,y2,z2] = sph2cart(lon2*pi/180,lat2*pi/180,R); 
z2(lon2<0) = nan; 
plot3(x2,y2,z2,'-','color',0.5*[1 1 1])

% an extra line at 0 longitude: 
[lon3,lat3] = meshgrid([0 180],linspace(-90,90,300)); 
[x3,y3,z3] = sph2cart(lon3*pi/180,lat3*pi/180,R); 
plot3(x3,y3,z3,'k-')

axis equal tight off

load topo
[Lon,Lat] = meshgrid(0.5:359.5,-89.5:89.5); 

topo(topo<=0) = nan; 
topo(Lon>180) = nan;
[X,Y,Z] = sph2cart(deg2rad(Lon),deg2rad(Lat),R+topo/10); % topo/10 produces 100x exaggeration

surf(X,Y,Z,topo); 
shading interp

view(43,39)

camlight 
material dull

[Marisabel Gonzalez]

How could you plot a lat/lot point and a declination and inclination point?

[Sam Polk]

@Chad Greene This is great! I modified your code using the wgs84Ellipsoid and geodetic2ecef functions to do these same plots on a spheroid (rather than a sphere). This code is given below:

% Plot lines of longitude: 
[lon_lon,lat_lon] = meshgrid(-180:lonspacing:180,linspace(-90,90,300)); % lat-long coordinates of our longitude mesh
[xlon,ylon,zlon] = geodetic2ecef(wgs84Ellipsoid('meter'), lon_lon, lat_lon, 0); % Converts to [x,y,z] on surface of earth
plot3(xlon, ylon, zlon ,'-','color',0.5*[1 1 1])
hold on

% Plot lines of latitude: 
[lat_lat,lon_lat] = meshgrid(-90:latspacing:90,linspace(-180,180,300)); % lat-long coordinates of our lattitude mesh
[xlat,ylat,zlat] = geodetic2ecef(wgs84Ellipsoid('meter'), lon_lat, lat_lat, 0); % Converts to [x,y,z] on surface of earth
plot3(xlat,ylat,zlat,'-','color',0.5*[1 1 1])

I had some trouble adding the plot of maps, however. Let me know if you have any suggestions!

Answer 2

[Chad Greene]

I turned my answer into a collection of functions called globeplot, globesurf, globegraticule, globeborders, etc. which you can find in the Climate Data Toolbox for Matlab.

[Margareta]

Dear Chad,

thank you so much for sharing the "half Earth" code example earlier (last September), and for also going to the trouble of providing this really nice and nifty set of functions as part of the CD toolbox!

Cheers from Sweden!

Maggie

[Chad Greene]

Thanks so much for saying that, Maggie!