Set colorbar ranges in 3d graphs

Hey, I would like to create a three dimensional surface using this:

">> a=X

a =

Columns 1 through 8

           0          50         100         150         200         250         300         350

Columns 9 through 16

         400         450         500         550         600         650         700         750

Columns 17 through 21

         800         850         900         950        1000

>> b=Y

b =

     0
    50
   100
   150
   200
   250
   300
   350
   400

>> c=Z

c =

Columns 1 through 8

           0           0           0           0           0           0           0           0
          16          32          67          98         127         164         194         234
         120         171         388         773        1086        1216        1770        2206
         189         270         494        1978        2755        3134        5060       10469
         133         166         183         348         647         937        1446        2304
         192         162         154         113         161         189         266         482
           0           0           0           0           0           0           0           0
           0           0           0           0           0           0           0           0
           0           0           0           0           0           0           0           0

Columns 9 through 16

           0           0           0           0           0           0           0           0
         366         604         529         504         346         226         228         179
        4027       11186       10276        5349        2560        1322         996         799
       27413       76387       37949       15591        5804        2654        1803        1069
        9844       24152       14772        4613        1777         849         459         290
        1288        2623        1538         582         280         148          90          56
           0           0           0           0           0           0           0           0
           0           0           0           0           0           0           0           0
           0           0           0           0           0           0           0           0

Columns 17 through 21

           0           0           0           0           0
         108          94          79           0           0
         646         476         612           0           0
         884         858         722           0           0
         266         215         139           0           0
          48          48          31           0           0
           0           0           0           0           0
           0           0           0           0           0
           0           0           0           0           0

>> surf(X,Y,Z)"

At the same time I would like to define that Z values < = 1803 will be shown with red color on the surface graph, 1803<Z<2755 yellow and Z > = 2755 green. How can I set the ranges of the colorbar in order to get this result? Thank you.

Answer 1

[Sven]

Hi Eleftheria,

You can use caxis() to set the colour limits (which is part of your problem... we'll get to the next bit).

Try this:

surf(X,Y,Z')
colorbar % This will show the colour axis
caxis([1803 2755])

But as you see, this just puts the limits to those ranges, but still has the gradiented colour map. Next, we need to set a new colour map:

colormap([1 0 0; 1 1 0; 0 1 0])

Did that do what you wanted?

[Elria]

Hi Sven! Thank you once again but I still got some trouble. This way the colormap has lowest limit 1803 and max 2755 but what I really want is Z values from 0 to 1803 to be red, from 1803 to 2755 to be yellow and from 2755 to 76387 to be green. What I get is that: http://www.flickr.com/photos/87753025@N03/8031780155/ What can I do? Thanks!

[Sven]

Everything below the lowest limit in caxis([low high]) will be coloured as low, everything above the high limit will be coloured as high.

Everything between the limits will be distributed evenly from low to high. So, I guess what you need is to set the caxis lower limit low enough below 1803 so that the transition from red to yellow occurs at 1803. Try this:

lowToHigh = [1803 2755]
caxis(lowToHigh + [-1 1]*diff(lowToHigh))