How to print parts that fit up against an existing surface

Can anyone provide a link to articles on how to "measure" a surface, such that a 3D printed part will fit against that surface? If the surface is irregular, there needs to be a way to measure it, so that the required information can be put in the program for that part.

Are there "scanners" that can do this, creating a "map" of the surface? On this page, http://www.capinc.com/support/tips/s...-part-modeling, there is a section titled "How Can I Measure the Overall Height of an Irregular Surface?" ....but it doesn't say much about how this is being done, just what it does.

For a simple example, let's say I had a more or less cone shaped part, and I want to 3D print a part that will drop down over the cone and fit up against it. By more or less, I mean the part just resembles a cone, it's not a perfect cone shape. How does one measure the cone, to know how to create the matching surface in the 3D printer?

I might have better luck searching, if I knew the proper terms for what I'm looking for - maybe that's why I'm having so much trouble finding the information.

There are indeed a wide variety of 3D scanners, it's a field of technology possibly more diverse than 3D printing.

The main technologies are:
laser tomography, which uses a laser or set of lasers and camera to detect contours. Most small turntable scanners use this.
Light Coding Or Stereoscopic scanning, which uses two (or more) cameras to get a 3D image or video. The Microsoft Kinect game system uses this, and many portrait and room scanners use this.
Photogrammetry, using regular photos of an object from many, many different angles under the same conditions to reconstruct the object as a computer model. A good (and free) example of this is Autodesk 123D Catch. Of course, since it's free, it takes a long time to process, and I'm pretty sure Autodesk gets to look in on your scans and use them if they want to.

Laser Tomography is great for scanning small things in high detail, Light Coding is great at scanning whole rooms or even whole building interiors, and Photogrammetry is great at taking portraits of living things (using many many small cameras in an array around the person or thing to take the pictures simultaneously)