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#!CSeaGreen #!N  #!Rrubsht 
Rubbersheet #!N #!EC #!N #!N Another technique used to visualize data 
collected on a 2-dimensional grid is sometimes called a "height map." 
In Data Explorer, the Rubbersheet module will generate this for you. 
Conceptually, a height map is drawn by elevating the 2-D grid 
into the third dimension. Call it the Z dimension, with our 
original grid lying in the X-Y plane. The height or Z-value 
given to each vertex of the original grid is proportional to 
the specified scalar data value at that vertex. If the data 
were vector data, you could elevate the grid by the magnitude 
of the vector, since magnitude is a scalar value. The result 
usually resembles something akin to a relief map of the surface 
of the Earth with hills and valleys. #!N #!N However, this 
brings up an important point that will occur elsewhere in Data 
Explorer (and visualization in general). Remember that the original data were 
collected on the X-Y plane (for example, our grass-counting botanist's data). 
It is one thing to indicate the different distributions of grass 
species by showing a 3-D plot of the numbers using a 
height map. But it is not correct to say, then, that 
the data values so shown were collected from these 3-dimensional positions: 
that would imply the botanist counted grass species growing in mid-air! 
This might be true in the Amazon, but not in Kansas. 
#!N #!N That is, we may have counted 2 species at 
the grid point [x=0, y=0]. If we Rubbersheet using the species 
count as the Z deflection value, our 3-D height map will 
now have a point at [x=0,y=0, z=2] (if the Rubbersheet "scale" 
is 1.0 and the minimum count in our data set is 
0). The data was not collected at that point but rather 
at [x=0,y=0, (z=0)]. For our convenience, Data Explorer maintains the original 
data values as if they were attached to the original grid. 
It is your responsibility to remember and, if necessary, make it 
clear to other viewers that the representation of the data in 
3-D is not a "realistic" image of the original 2-D sampling 
space. Rather, Rubbersheet is used to visualize the "ups and downs" 
in the data Field as actual differences in height. This is 
a very powerful visualization technique because of our familiarity with actual 
heights in everyday experience. One simple way to show viewers the 
difference is to make two copies of the Field by taking 
two wires from the output tab of the Import module you 
use to import the data Field. Connect one wire to a 
Color module with a Colormap attached, but leave the Field 2-dimensional. 
Arrange the 2-D colored grid such that the viewer is looking 
straight down on it. Connect the second wire from Import to 
Rubbersheet and then use a second Color module, but run wires 
from the same Colormap as you used to color the first 
copy. The second copy, a 3-D colored "height Field," can then 
be rotated into a "perspective" view. The result will be a 
Field both colorized according to the data values and also elevated 
into the third dimension according the same data values. This redundancy 
is often more instructive than either visualization technique used alone. #!N 
#!N #!N  #!F-adobe-times-medium-i-normal--18*   Next Topic #!EF #!N #!N  #!Ltrastr,dxall606 h Transformations and Structuring  #!EL  #!N  #!F-adobe-times-medium-i-normal--18*   
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