So I’m looking for a mat for people to stand on in my full body scanner that allows me to easily cut off anything below their feet as well as set ground control points.
In this video (https://www.youtube.com/watch?v=0hTyEhbmjFE&feature=youtu.be) there’s a large white mat with a black rectangular outline along the edge for setting GCP’s. I’d like something similar to this, but I’m not sure what to look for. I’m also not sure how easily I could cut off the bottoms of peoples feet with this.
Any suggestions?
Just put some tape on the floor 
You need something :
-that does not bend, hard enough so the surface does not move. Depending on your rig, you don’t want the surface to move at all while you are scanning. And, if you are using a pre-aligned workflow, you don’t want the mat to move between shoots, which is even harder.
-with enough features : you can use any unique pattern to help RC to align. You also need to include known distances so you can scale your object. Your features need to be easily pointable on pictures : a line is not that good, a cross is better…
(I had very good results with chromatic noise generated in GIMP (over black for projection or over white for printing) + a few named contrasting cross to have easily pointable control points)
-you could use the new RC generated coded markers so you can automate the control points part. I didn’t try this but this is planned.
If you really want to make the editing easier, you could ask your people to stand on a piece of wood to add 1 cm on top of the mat, so this is really easy to filter out the 3D object/people without cutting the bottom of the shoes / feet.
One last thing, make sure you are perfectly level (horizontal) with a bubble level. You can use some height-adjustable feet to make sure your mat is perfectly leveled. Because your points on the map will be real ground control points, so they need to be on the ground plane.
Of course, not absolute rules, this is all about experiment and try and error !
Or just mask off the for and paint it.
Johanthan is right though it can not move one bit. For some reason I imagine a concrete floor and paint would be cheap, easy, durable, and never move.
Toothbrush dipping painting ? 
Anything that creates unique features is good, digital or “analog” !
I imagine what JOHN described is to basically to create a very limited white box.
The idea is to create an area around the target with as few identifiable marks as possible. Ideally RC won’t find any on the white mat (it’s not the color that counts but the uniformity, however white has no color altering propertes and also improves lighting from the bottom) and then not model anything apart from the shoes. This will probably not be perfect though because there will probably always be some shadow close to the shoes which RC might still be able to latch onto…