Solving the Raster to Vector Conversion Dilemma
Sooner or later, everyone who scans an engineering drawing or construction drawing will need to convert the scanned file to a CAD file – maybe AutoCAD, Revit, Solidworks, VectorWorks, or some other CAD program. Regardless of how experienced you may be in operating your CAD software, converting the scanned file to a CAD file can present a dilemma.
The reason for this dilemma is two-fold. First of all, many people don’t realize when they’re scanning the original drawing that they need to scan in a particular way if they plan to convert it to CAD later; and, even if they do scan properly, they don’t have the knowledge or experience to properly convert the drawing.
While it’s true that most CAD software programs do offer some raster to vector conversion capabilities, if you don’t understand the process, you’ll probably not get the conversion results you hoped for. Then, you’ll probably just give up and recreate the drawing from scratch. So, what’s the point of scanning in the first place, if you’re not able to convert to CAD easily?
Curiously, even for those who understand the process of raster to vector conversion, what most often is missing from the underlying experience of knowing what will work for each scanned file. Each image is different and it’s very rare that two different images will respond with equal success to the same method of conversion. One might say that this is where we step from the “science” of r2v conversion to the “art” of conversion. It takes the experience to know which method or combination of methods will work for each individual raster file.
This is where the “art” comes in… knowing which method will work for each drawing. And sometimes, it’s not just one method; it may be a combination of two or more methods used in one drawing. So, raster to vector conversion is a combination of having a properly scanned raster image and an experienced blending of the science and the art of conversion.
Using the Right Scanned Image
First, and foremost, the raster image must be of good quality. This usually means that the first step in the conversion process is cleaning up the files. This may include any or all of the following:
- De-skewing images — A skewed image occurs when a paper drawing has been fed through a scanner at an angle so that the lines are no longer perpendicular to the raster image. This skewing can cause significant deterioration during the vectorization process. Therefore, the image should either be re-scanned or re-drawn prior to the raster to vector conversion image quality in order to assure good results.
- De-speckling images — Images with dots or smudges that may have occurred as a result of dirt on the scanner glass during the scanning process, or that may be inherent in the original drawing…coffee stains, erasure marks, slight tears, and wrinkles etc., need to be cleaned by a process known as de-speckling. This process is relatively straight-forward. However, solid black areas that obscure the drawing are more problematic and will require an expert in order to recreate the drawing in its original form.
- De-Dithering lines –of the lines on your image are dithered, you can see when they are magnified that they are made up of black speckles. The easiest way to correct this is by rescanning the drawing with more appropriate scanner settings. However, if this is not possible, a raster to vector professional will likely have specialized tools that can mend the dithered lines.
- Filling in holes in the lines — A good raster to vector converter, in the hands of an experienced r to v engineer should be able to correct this problem with a minimum of fuss. Provided that the holes are not too large, this is just a matter of filling in the lines.
- Fixing broken lines — Automatic raster to vector converting software usually includes a technology called “gap jumping”. This means that when they vectorize a raster image they are able to “jump” over small breaks automatically. However, if the lines are very broken, call in the experts. If you don’t know what you’re doing, this can take forever to fix.
Getting a Good CAD File
Once you have a cleaned-up raster file, then you can start the process of converting to a CAD file. CAD files are vector files. Vector graphics are composed of mathematically drawn lines, points, and fills. That’s why we spend so much time correcting the “lines” in the raster file. Those raster lines are made up of pixels that must be lined up and must be clean and solid if they’re going to convert properly into the real mathematical lines of a CAD drawing.