Frame for 3-D map display
This map display is based on a coordinate transformation and is not a true map projection.
Meridians, parallels, and displayed map data appear in a 3-D view that depends on the
view and camera settings of the map axes. Change the view interactively or by using the
view function. Change the camera
settings using the
In the 3-D sense,
globe is true in scale, equal-area, conformal, minimum
error, and equidistant everywhere.
globe has none of the distortions inherent in planar
projections, it cannot be displayed without distortion or in its entirety. In order to
render the globe in a figure window, either a perspective or orthographic transformation
must be applied, both of which necessarily involve setting a viewpoint, hiding the back
side and distortions of shape, scale, and angles.
The globe requires no standard parallels.
globe display allows you to visualize terrain relief or other
data for an entire planet viewed from space. Its underlying transformation maps
latitude, longitude, and elevation to a 3-D Cartesian frame. The
globe display is different from other transformations because
it can render relative relief of elevations above, below, or on a sphere.
When displayed, the globe looks like an orthographic azimuthal projection, provided
Projection property of the map axes is set to
Display geoid heights from the EGM96 geoid model over a 3-D globe. First, get geoid heights and a geographic postings reference object. Load coastline latitude and longitude data.
[N,R] = egm96geoid; load coastlines
Create a frame for the 3-D globe display using
axesm. Set the line of sight for the globe using
view. Turn off the axes background using
axis off. Then, display the geoid heights and coastline data.
axesm('globe','Grid','on') view(60,60) axis off meshm(N,R) plotm(coastlat,coastlon)
Display a polygon on a globe by converting the polygon to a data grid.
Create a sample polygon that contains a hole and rests on the surface of the globe. To do this, generate the vertices of its external and internal boundaries using the
outlinegeoquad function. Specify the geographic limits as the first two arguments, and the vertex spacing in degrees as the next two arguments. Reverse the order of the internal boundary vertices using the
flip function, so they are in a counterclockwise order.
[latE,lonE] = outlinegeoquad([-35 35],[-30 30],0.25,0.25); [latI,lonI] = outlinegeoquad([-15 15],[-15 15],0.25,0.25); latI = flip(latI); lonI = flip(lonI);
Combine the vertices into a single list by separating the boundaries with
lat = [latE NaN latI]; lon = [lonE NaN lonI];
lon represent the boundaries of a polygon that contain a hole. Display the boundaries on the globe as a filled polygon by converting the polygon to a data grid.
To do this, create a geographic cells reference object for the globe and a grid of ones. Replace elements of the grid with the polygon data using the
vec2mtx function. The new grid contains 0s to indicate the inside region of the polygon, 1s to indicate the boundaries, and 2s to indicate the outside region of the polygon.
R = georefcells([-90 90],[-180 180],0.25,0.25); V = ones(R.RasterSize); [V,R] = vec2mtx(lat,lon,V,R,'filled');
Create a globe using the
axesm function. Display the data grid as an image using the
geoshow function. Adjust the colormap so the inside region of the polygon is purple and the outside region is white. Change the camera line of sight using the
view function, so the polygon is displayed on the near side of the globe.
axesm('globe','Grid','on') geoshow(V,R,'DisplayType','texturemap') colormap([0.5 0.5 0.8; 0 0 0; 1 1 1]) axis off view(100,20)
The appearance of polygons on the globe is dependent on the camera line of sight and the globe transparency. For example, make the globe slightly transparent using the
When you view the polygon from the near side of the globe, the external boundary vertices appear in a clockwise order. When you view the polygon from the far side of the globe, the external boundary vertices appear in a counterclockwise order. When you rotate the globe so the polygon appears on both the near side and far side, then the polygon appears to intersect itself.