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Member "dx-4.4.4/help/dxall605" (5 Feb 2002, 3404 Bytes) of package /linux/misc/old/dx-4.4.4.tar.gz:


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    1 #!F-adobe-helvetica-medium-r-normal--18*
    2 #!N 
    3 #!CSeaGreen #!N  #!Rrubsht 
    4 Rubbersheet #!N #!EC #!N #!N Another technique used to visualize data 
    5 collected on a 2-dimensional grid is sometimes called a "height map." 
    6 In Data Explorer, the Rubbersheet module will generate this for you. 
    7 Conceptually, a height map is drawn by elevating the 2-D grid 
    8 into the third dimension. Call it the Z dimension, with our 
    9 original grid lying in the X-Y plane. The height or Z-value 
   10 given to each vertex of the original grid is proportional to 
   11 the specified scalar data value at that vertex. If the data 
   12 were vector data, you could elevate the grid by the magnitude 
   13 of the vector, since magnitude is a scalar value. The result 
   14 usually resembles something akin to a relief map of the surface 
   15 of the Earth with hills and valleys. #!N #!N However, this 
   16 brings up an important point that will occur elsewhere in Data 
   17 Explorer (and visualization in general). Remember that the original data were 
   18 collected on the X-Y plane (for example, our grass-counting botanist's data). 
   19 It is one thing to indicate the different distributions of grass 
   20 species by showing a 3-D plot of the numbers using a 
   21 height map. But it is not correct to say, then, that 
   22 the data values so shown were collected from these 3-dimensional positions: 
   23 that would imply the botanist counted grass species growing in mid-air! 
   24 This might be true in the Amazon, but not in Kansas. 
   25 #!N #!N That is, we may have counted 2 species at 
   26 the grid point [x=0, y=0]. If we Rubbersheet using the species 
   27 count as the Z deflection value, our 3-D height map will 
   28 now have a point at [x=0,y=0, z=2] (if the Rubbersheet "scale" 
   29 is 1.0 and the minimum count in our data set is 
   30 0). The data was not collected at that point but rather 
   31 at [x=0,y=0, (z=0)]. For our convenience, Data Explorer maintains the original 
   32 data values as if they were attached to the original grid. 
   33 It is your responsibility to remember and, if necessary, make it 
   34 clear to other viewers that the representation of the data in 
   35 3-D is not a "realistic" image of the original 2-D sampling 
   36 space. Rather, Rubbersheet is used to visualize the "ups and downs" 
   37 in the data Field as actual differences in height. This is 
   38 a very powerful visualization technique because of our familiarity with actual 
   39 heights in everyday experience. One simple way to show viewers the 
   40 difference is to make two copies of the Field by taking 
   41 two wires from the output tab of the Import module you 
   42 use to import the data Field. Connect one wire to a 
   43 Color module with a Colormap attached, but leave the Field 2-dimensional. 
   44 Arrange the 2-D colored grid such that the viewer is looking 
   45 straight down on it. Connect the second wire from Import to 
   46 Rubbersheet and then use a second Color module, but run wires 
   47 from the same Colormap as you used to color the first 
   48 copy. The second copy, a 3-D colored "height Field," can then 
   49 be rotated into a "perspective" view. The result will be a 
   50 Field both colorized according to the data values and also elevated 
   51 into the third dimension according the same data values. This redundancy 
   52 is often more instructive than either visualization technique used alone. #!N 
   53 #!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*   
   54 #!N