Hot & Cold Colors
Windows only

## Problem

It is often useful to show curvature with a color index. For example, if you divide a curve into 500 points and measure the curvature at each point, you can assign a “curvature radius” color to each of the points using RhinoScript. Let’s take a look at how this is done.

## Solution

One solution you might consider is to determine the minimum and maximum curvature values for your samples. Then, you can use this function to calculate a color value for each point.

'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
' Return a RGB color given a scalar v in the range [vmin, vmax].
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
Function GetHotColdColor(v, vmin, vmax)

Dim r, g, b, dv
r = 1.0 : g = 1.0 : b = 1.0 'white

If (v < vmin) Then v = vmin
If (v > vmax) Then v = vmax
dv = vmax - vmin

If (v < (vmin + 0.25 * dv)) Then
r = 0
g = 4 * (v - vmin) / dv
ElseIf (v < (vmin + 0.5 * dv)) Then
r = 0
b = 1 + 4 * (vmin + 0.25 * dv - v) / dv
ElseIf (v < (vmin + 0.75 * dv)) Then
r = 4 * (v - vmin - 0.5 * dv) / dv
b = 0
Else
g = 1 + 4 * (vmin + 0.75 * dv - v) / dv
b = 0
End If

GetHotColdColor = RGB(Int(r*255), Int(g*255), Int(b*255))

End Function

Here is a sample script that you can use to test the above function…

'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
' Test procedure creates a "hot-to-cold" color ramp mesh.
' To see the results, set a viewport to "rendered" display.
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
Sub TestGetHotColdColor()

' Mesh with 200 vertices and 100 faces
Dim v(199), f(99), c(199), ub, i

' Fill in arrays
ub = UBound(v)
For i = 0 To UBound(v) Step 2
v(i) = Array(i/2,0,0)
v(i+1) = Array(i/2,10,0)
c(i) = GetHotColdColor(i,0,ub)
c(i+1) = c(i)
f(i/2) = Array(i,i+2,i+3,i+1)
Next

' Create the mesh object