Our desktop Web App is Takeoff Lite, a construction estimating website. Part of what we allow our users to do is use their mouse to measure areas, lengths, and counts on an uploaded PDF file. We have been using Draw2D but we need a more powerful and slicker tool to so measurements with our “skin” on it. The first phase would be to get the basic functions working as they are on our site currently.
https://pdfjs.express/samples/advanced/measurement/
[Takeoff Lite – Everything for the small contractor] http://takeofflite.com