CGAL, the Computational Geometry Algorithms Library, is a large C++ library of geometric data structures and algorithms such as Delaunay triangulations, mesh generation, Boolean operations on polygons, and various geometry processing algorithms. CGAL is used in various areas: computer graphics, scientific visualization, computer aided design and modeling, geographic information systems, molecular biology, medical imaging, robotics and motion planning, and numerical methods.
Engauge Digitizer is digitizing software that converts an image showing a graph or map into numbers. The image file can come from a scanner, digital camera, or screenshot. The numbers can be read on the screen, and written or copied to a spreadsheet. Highlights for beginners include an intuitive interface and extensive context-sensitive documentation. Highlights for experts include compensation for image distortion, cartesian and polar coordinates, linear and logarithmic coordinates, automatic scanning, graphical previews, and browser help.
ImageJ is an image processing program inspired by NIH Image for the Macintosh. It can display, edit, analyze, process, save, and print 8-bit, 16-bit, and 32-bit images. There are modules for biology, astronomy, nuclear medicine, physics, and more. If you can take a picture of something, whether with a microscope, a telescope, an oscilloscope, an xray machine, or a scanner, then this program will let you enhance, manipulate, and measure the results.