Raster to Vector – Connecting the Dots (Literally)
When a blueprint, engineering drawing, or graphic design is scanned, the resulting digital file is a raster file. In order to make changes to the drawing or design using a CAD program, such as AutoCAD, the raster file must be converted to a vector file. Quite literally, this does require connecting the dots since a raster file is a collection of pixels. A pixel is a physical point (or dot) in a raster image. It is the smallest addressable element in a display device; so it is the smallest controllable element of a picture represented on the screen. The address of a pixel corresponds to its physical coordinates. LCD pixels are manufactured in a two-dimensional grid and are often represented using dots or squares. Pixels are what you see when you enlarge a low-resolution image.
Wikipedia tells us that a vector file, on the other hand, “makes use of geometrical primitives such as points, lines, curves, and shapes or polygon(s), which are all based on mathematical expressions, to represent images in computer graphics.” Essential, vectors are lines or paths leading through control points on the drawing, with each point having a geographic position on an x – y-axis. Vectors can be assigned a color, a shape, a thickness and also a fill.
When you convert a raster file to a vector file, you literally have to connect the dots by converting the rasters into lines. Raster files, as noted above begin to break apart (pixelate) when you enlarge them and you lose the clarity of the image. On the other hand, a vector image can be enlarged indefinitely without loss of integrity, because it is made of lines, arcs, and shapes or polygons. This connecting the dots, or raster to vector conversion is used for commercial and industrial applications when scanned technical drawings, maps, and other paper graphics need to be converted to CAD files.
One way to ensure the success of the raster to vector conversion is to start with a high-quality scan. The scanner that is used to scan paper drawings for raster to vector conversion should be one that is capable of providing a high-quality raster image. Image quality is very important. 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.
The Process of Raster to Vector Conversion (How to Connect the Dots)
There are many different conversion methods. There is 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, we have found that one raster to vector conversion product does not fit all. It is not uncommon with 100 drawings, that 30% is converted via one (1) method, the next 40% need to converted via a different method, and the remaining are hand redrawn.
Don’t 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, we 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 programs 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 programs.
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.
Connecting the dots may seem like child’s play, but when the accuracy of a construction or manufacturing drawing is at stake, it’s anything but!