Raster to Vector (or R2V) is used extensively in commercial and industrial applications to convert technical drawings, maps and other paper graphics from scanned raster files to vector formats. The process starts with a high quality scan.
Scanning
When a paper drawing is scanned, the resulting digital file is a raster file. The large format scanner used to scan paper drawings for raster to vector conversion should be a scanner that is capable of providing a high quality image. Image quality is everything here. If two lines are muddied and appear as a single line in the scanned drawing it will be difficult, if not impossible, to know that they should be separated when the scanned raster image is converted to a vector image. Once you have the best scanned raster image possible, rectify the image to make sure it is aligned correctly, scaled correctly, and that it measures correctly on all axes points.
Converting
In order to work with a digital file in a CAD (Computer Aided Design) system, the scanned raster file needs to be converted to a vector file by a process called raster to vector conversion or, simply, vectorization. According to Wikipedia, “vectorization refers to the process of converting raster graphics into vector graphics.” In very simple terms, this means converting pixels, which are dots of color (raster) like this . . . . . . . . . . . into lines (vectors) like this __________. It’s important to note that when you enlarge a raster image, the dots or pixels begin to break apart, and you lose the clarity of the image. (Think about enlarging a photo taken with your digital camera). On the other hand, a vector image can be enlarged indefinitely without loss of integrity, because it is made of lines, arcs, polygons, etc.
But how exactly to convert from raster to vector?
There are many different conversion methods. There are commercially available raster to vector conversion software packages from companies like GTX, Hitachi, I/Vector, and Softelec. Some conversion service companies have written their own raster to vector conversion routines. Unfortunately I have found that one raster to vector conversion product does not fit all. It is not uncommon with 100 drawings, that 30% are converted via one (1) method, the next 40% need to converted via a different method, and the remaining are hand redrawn.
Please do not be misled with raster to vector software vendors promising 'automatic raster to vector conversion'. Simply put, it is not true. These products are tools - and only tools. They all can help in the conversion process, but they are not the cure-alls they claim to be.
Generally, I have found that the most reliable way to get “CAD Perfect” digital drawings is by using an experienced raster to vector conversion service. Make sure the firm has proven and verifiable capability to provide converted files that can be brought into your AutoCAD , Microstation, or other CAD program that you use. Make sure that the conversion service you choose is able to provide vector files that are easily editable in your PC CAD, CNC, GIS or other program.
Finally, confirm that the raster to vector conversion service that you use provides quality control and a satisfaction guarantee. The work should be guaranteed to be 100% correct, 100% of the time. No exceptions. No excuses.
