Some of the problems of the raster to vector conversion method method are detailed below:
Layering
The resulting CAD file is typically in one layer. Some applications will put each line weight on a different layer, but only if there is a clear difference in line thicknesses.
Linetypes
Any linetype, besides continuous, will convert each dash or segment to a separate and unrelated line entity.
Arcs and Circles
Arcs and circles are typically converted to a series of short, unrelated line segments Some applications may convert them to a series of arcs. Conversion to a circle or a single arc is difficult because most hand drawn work is actually elliptical.
Text
Text is typically converted so that each character is actually many small line segments. Not recognizable text.
Dimensions
Dimensions are converted to an unrelated assortment of lines with no association to each other or the item they describe.
Symbols
The raster to vector conversion will convert each symbol to numerous unrelated line segments.
Hatch Patterns
All hatch patterns will be converted as enormous numbers of unrelated line segments.
Attributes
Attributes or database information cannot be assigned with automatic raster conversion.
Conversion of Extraneous Information
Besides the problems in correctly converting the real data in a drawing, automatic raster conversion will put every speckle, crease, stain, and smudge into the CAD file.
Gaps
Imperfections or light areas in the lines on the original drawing are frequently interpreted as genuine white space. The resulting conversion will have small gaps in the middle of lines that should be continuous.
Missing Information
The effort to automatically distinguish between extraneous information and real data often results in arbitrary elimination of real data in the converted drawing.
Style
With other conversion methods, a consistent style for dimensions, symbols, text height, fonts, etc, can be applied as the conversion is performed. With automatic techniques the style of the drawing cannot be changed.
Limitations of Scanning Resolution
If the originals are not scanned at high enough resolution, problems can occur with lines that intersect at an angle. The resulting product of automatic raster-to-vector conversion can, of course, be corrected by CAD operators after the fact. Unfortunately, the labor and cost for this type of cleanup typically exceeds the cost of the other methods. |