Now we come to part wherein I take the previous constraints, and design a holster. I make each of my holsters by hand, one by one, for specific firearms. Each one is an original, and I've not yet made a true duplicate yet. I have the general purpose, general design, and some of the constraints, but at this point in the process, I'm missing some very important details. That's when I suddenly had an idea. I asked for a photograph of the actual end user, wearing the most likely clothing and belt when using the holster, holding the gun as though drawing. This gave me some very important details (in fact, I've had everyone since then do the same thing): I now know where they wanted to put the gun on the their waist, what the natural cant of holster would be, and what height they wanted their sidearm to sit at. The best way to get this picture is to have the end user pose in this manner, and take the picture as square to the gun as possible.
I can then print the picture and use it as a reference. To figure cant, I take the printed photo, draw lines along the top of the belt and the center of the bore, and measure the angle from vertical (perpendicular to the belt). To figure height, I compare the location of the top of the belt to the trigger guard and slide. Now, I can do a quick sketch to decide what the holster will look like. Sometimes actual placement of the firearm doesn't work- for example, the placement of the belt would interfere with proper grip, or the gun would be so high on the belt as to be unstable. In most cases, these issues can be identified in the sketch and figured out before the leather is cut.
Stay tuned, plenty more on this to come!