Graphic app snaps lines over your hand drawing

Pardon me if this is already available. I don't know what terms to search for, other than something like "auto snap to," to see if such software is available. I think a big obstacle in spreading 3-D printing to the masses is users having to learn CAD to draw what they want to print. I can draw a picture on a napkin and place measurements on it, but it would take me forever to reproduce that picture in a CAD program. CAD has a high learning curve. I would like to make an image file of the 2D napkin art using a scanner or camera, point the CAD program to the file, and let the CAD program make it look professional by snapping my drawn lines to a grid, replacing my geometric hand-drawn shapes with shapes from a library, and applying the measurements I have written in using handwriting reading software [2], all in order to make a 3D drawing. I know some smart phone faxing apps will automatically align text [1] so the technology is part way there.

Edit 2013-09-20 This odd program, not for sale yet apparently, seems to recognize, lock in on and copy part of an image so it can be pasted it elsewhere. At 4:56 into the video a hand drawn wine glass seems to be "lassoed" (I don't know how to otherwise explain it as it's impossible to properly explain something one doesn't understand) and then converted into a CAD quality image [3]. Per the video comments, this is apparently revolutionary to experts in the CAD field -- I wouldn't know the difference. The fact that a complex part of an image can be identified and locked in on is promising to me as far as my idea is concerned. A comparison to this "locking in" ability would be when one is previewing a document before a scan and during the preview the scanner software tries to detect the edges of the object, differentiate the object from the background, and crop and scan only the pertinent part of what is on the scanner bed at the moment minus the background; there is some image recognition intelligence there.

2019 12 28: Maybe sketch out the idea on onion skin paper placed over isometric drawing paper (free templates on the net), tape the onion skin paper over the computer monitor, snap the lines following the onion skin drawing.