Graphics |
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.
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
CmLength
)
BeginSlot)
EndSlot
)
CData
values of the graphic objects contained in the axes. That is, the values of the axes CLim
property determined by MATLAB when CLimMode
is auto
(CDmin
and CDmax
).
First, define subplot regions and plot the surfaces.
ax1 = subplot(2,1,1); view([0 80]) surf(topodata) shading interp ax2 = subplot(2,1,2),; view([0 80]); surfl(topodata,[60 0]) shading interp
Concatenate two colormaps and install the new colormap.
Obtain the data you need to calculate new values for CLim
.
CmLength = size(get(gcf,'Colormap'),1);% Colormap length
BeginSlot1 = 1;% Beginning slot
EndSlot1 = size(Lightingmap,1);% Ending slot
BeginSlot2 = EndSlot1+1; EndSlot2 = CmLength; CLim1 = get(ax1,'CLim');% CLim values for each axis
CLim2 = get(ax2,'CLim');
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 colormap
PBeginSlot = (BeginSlot - 1) / (CmLength - 1); PEndSlot = (EndSlot - 1) / (CmLength - 1); PCmRange = PEndSlot - PBeginSlot;% Determine range and min and max
% of new CLim values
DataRange = 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
Use the newclim
M-file to set the CLim
values of each axes. The statement
sets the 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.
The 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
-0.4]
. To color this surface with slots 65 to 120, newclim
computed new CLim
values of [0.4
-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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