Example -- Simulating Multiple Colormaps in a Figure
Suppose you want to display two different surfaces in the same figure and color each surface with a different colormap. You can produce the effect of two different colormaps by concatenating two colormaps and then setting the
CLim property of each axes to map into a different portion of the colormap.
This example creates two surfaces from the same topographic data. One uses the color scheme of a typical atlas -- shades of blue for the ocean and greens for the land. The other surface is illuminated with a light source to create the illusion of a three-dimensional picture. Such illumination requires a colormap that changes monotonically from dark to light.
Calculating Color Limits
The key to this example is calculating values for
CLim that cause each surface to use the section of the colormap containing the appropriate colors.
To calculate the new values for
CLim, you need to know
CDatavalues of the graphic objects contained in the axes. That is, the values of the axes
CLimproperty determined by MATLAB when
First, define subplot regions and plot the surfaces.
Concatenate two colormaps and install the new colormap.
Obtain the data you need to calculate new values for
Defining a Function to Calculate CLim Values
Computing new values for
CLim involves determining the portion of the colormap you want each axes to use relative to the total colormap size and scaling its
Clim range accordingly. You can define a MATLAB function to do this.
function CLim = newclim(BeginSlot,EndSlot,CDmin,CDmax,CmLength)
% Convert slot number and range
% to percent of colormapPBeginSlot = (BeginSlot - 1) / (CmLength - 1); PEndSlot = (EndSlot - 1) / (CmLength - 1); PCmRange = PEndSlot - PBeginSlot;
% Determine range and min and max
% of new CLim valuesDataRange = CDmax - CDmin; ClimRange = DataRange / PCmRange; NewCmin = CDmin - (PBeginSlot * ClimRange); NewCmax = CDmax + (1 - PEndSlot) * ClimRange; CLim = [NewCmin,NewCmax];
The input arguments are identified in the bulleted list above. The M-file first computes the percentage of the total colormap you want to use for a particular axes (
PCmRange) and then computes the
CLim range required to use that portion of the colormap given the
CData range in the axes. Finally, it determines the minimum and maximum values required for the calculated
CLim range and returns these values. These values are the color limits for the given axes.
Using the Function
newclim M-file to set the
CLim values of each axes. The statement
CLim values for the first axes so the surface uses color slots 65 to 120. The lit surface uses the lower 64 slots. You need to reset its
CLim values as well.
How the Function Works
MATLAB enables you to specify any values for the axes
CLim property, even if these values do not correspond to the
CData of the graphics objects displayed in the axes. MATLAB always maps the minimum
CLim value to the first color in the colormap and the maximum
CLim value to the last color in the colormap, whether or not there are really any
CData values corresponding to these colors. Therefore, if you specify values for
CLim that extend beyond the object's actual
CData minimum and maximum, MATLAB colors the object with only a subset of the colormap.
newclim M-file computes values for
CLim that map the graphics object's actual
CData values to the beginning and ending colormap slots you specify. It does this by defining a "virtual" graphics object having the computed
CLim values. The following picture illustrates this concept. It shows a side view of two surfaces to make it easier to visualize the mapping of color to surface topography. The virtual surface is on the left and the actual surface on the right. In the center is the figure's colormap.
The real surface has
CLim values of
0.4]. To color this surface with slots 65 to 120,
newclim computed new
CLim values of
1.4269]. The virtual surface on the left represents these values.
|Axes Color Limits -- the CLim Property||Defining the Color of Lines for Plotting|
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