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Displaying Topographic Data

This example shows several ways to represent the Earth's topography. The data used in this example are available from the National Geophysical Data Center, NOAA US Department of Commerce under data announcement 88-MGG-02.

About the Topography Data

The data file, topo.mat, contains topographic data. topo is the altitude data and topomap1 is a colormap for the altitude.

load topo topo topomap1    % load data 
whos('topo','topomap1')
  Name            Size              Bytes  Class     Attributes

  topo          180x360            518400  double              
  topomap1       64x3                1536  double              

Create Contour Plot

One way to visualize topographic data is to create a contour plot. To show the outline of the Earth's continents, plot points that have zero altitude. The first three input arguments to contour specify the X, Y, and Z values on the contour plot. The fourth argument specifies the contour levels to plot.

x = 0:359;                                % longitude
y = -89:90;                               % latitude

figure
contour(x,y,topo,[0 0])

axis equal                                % set axis units to be the same size
box on                                    % display bounding box

ax = gca;                                 % get current axis               
ax.XLim = [0 360];                        % set x limits
ax.YLim = [-90 90];                       % set y limits
ax.XTick = [0 60 120 180 240 300 360];    % define x ticks
ax.YTick = [-90 -60 -30 0 30 60 90];      % define y ticks

View Data as Image

You can create an image of the topography using the elevation data and a custom colormap. The topography data is treated as an index into the custom colormap. Set the CDataMapping of the image to 'scaled' to linearly scale the data values to the range of the colormap. In this colormap, the shades of green show the altitude data, and the shades of blue represent depth below sea level.

image([0 360],[-90 90], flip(topo), 'CDataMapping', 'scaled')
colormap(topomap1)

axis equal                                % set axis units to be the same size

ax = gca;                                 % get current axis               
ax.XLim = [0 360];                        % set x limits
ax.YLim = [-90 90];                       % set y limits
ax.XTick = [0 60 120 180 240 300 360];    % define x ticks
ax.YTick = [-90 -60 -30 0 30 60 90];      % define y ticks

Use Texture Mapping

Texture mapping maps a 2-D image onto a 3-D surface. To map the topography to a spherical surface, set the color of the surface, specified by the CData property, to the topographic data and set the FaceColor property to 'texturemap'.

clf
[x,y,z] = sphere(50);          % create a sphere 
s = surface(x,y,z);            % plot spherical surface

s.CData = topo;                % set color data to topographic data
s.FaceColor = 'texturemap';    % use texture mapping
s.EdgeColor = 'none';          % remove edges
s.FaceLighting = 'gouraud';    % preferred lighting for curved surfaces
s.SpecularStrength = 0.4;      % change the strength of the reflected light

light('Position',[-1 0 1])     % add a light

axis square off                % set axis to square and remove axis
view([-30,30])                 % set the viewing angle

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