The best way to digitize a dash board is a self positioning scanner like the ZCorp or Creaform scanner. $30,000+. Romer/Faro arms have trouble moving around in a car interior.
For the cheap DIYer:
1) Buy a cheap laser line tool. Position it (on the headliner?) to project a straight horizontal reference line across the bottom of the dash.
2) Use tape to draw straight vertical cross sections across the dash at regular increments (say 1"?).
3) Buy a cheap 12" profile gauge at Harbor Freight tools.
3) Position the top or bottom of the profile gauge on on the laser line. Press the profile gauge to the dash at each tape line, and scan each profile with a flatbed scanner.
4) Scale the images correctly, and trace each profile as a 2D spline/line/curve section in Rhino (free trial) or any CAD package that can import Bitmap images (like photo scans).
5) Create surface patches from the curves in 3D CAD package.
This will give you a basic outline of the dash shape. You can add additional detail with manual measurements to get a more accurate model.
It is a lot of work, but sure beats spending $30,000 only to find out there is still a lot more work.
-Dan
Global Inspection Solution
www.globalinspectionsolutions.com