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manual data conversion
Scanning a drawing produces a raster image, but does not convert the drawing to a vector file, which is a CAD document that may be edited with a CAD program.

A raster image may be automatically converted to vector format by a software program, but this approach is hindered by the capacity of the software application to interpret depth and geometry from the bits and pixels that make up a drawing. Due to software limitations, automatic raster-to-vector conversion may result in errors in the recognition of layers, linetypes, arcs and circles, text, dimensions, symbols, hatch patterns, and styles. In addition, creases, stains and smudges may not be distinguished from real data, thereby introducing extraneous information into the CAD file; gaps, imperfections in the original drawing, and missing information that would be interpolated by a CAD operator, may be mis-interpreted by the software as white space in the converted drawing.

A drawing converted by software algorithms may therefore require significant corrections and cleaning up by a CAD operator, who --with human perception and cognition-- is better equipped to make the sophisticated decisions involved. The final cost of the automated conversion can thus add up to the same amount or, even, more than would be incurred by using a CAD operator to perform a precision redraw from the beginning. The critical factor determining the final cost of the drawing conversion depends more on CAD labor costs than on the initial outlay to acquire, operate, and maintain software for automated conversion.

The best option for the conversion of drawings to CAD documents --the most effective in cost and in the quality of the result-- is therefore to utilize Sirius Digital Archiving's services for manual conversion by wholesale precision redraw. Our staff of experienced professional CAD operators, located off-shore, can offer the highest quality at the most competitive prices.

Free sample conversions are available, for your evaluation of our services.

The Difference Between a Raster Image and a Vector File


A raster image is a digital representation consisting of values assigned to each dot comprising the image. The number of possible values that may be assigned to each dot --also called a picture element or a pixel-- varies with the format selected for image representation and data storage. In a two-bit (or binary) file, each pixel is designated as being either black or white. In the case of an eight-bit grey-scale image, each dot may be assigned a different level of 256 shades of grey, with gradations from white to black. And, in a twenty-four bit color image, each pixel may be any one of several million (16,777,216) possible colors. Images of greater depth require more disk space to accomodate the increasing number of possible values that may be assigned to each pixel.

A raster image is created at a particular concentration of dots; the degree of resolution is typically measured in terms of dots per inch.

A raster file is thus a digital photograph and can be edited only by adjusting the values of individual pixels, of which there are may be thousands in each square inch of a drawing.

A vector file, on the other hand, is a database of descriptions of geometrical entities, represented by the projection of vectors on a cartesian coordinate system. The database of geometrical entities is created and maintained by a software application, such as a Computer Aided Design (CAD) program.

A vector file has two important advantages over a raster image. First, a vector format is more efficient and tends to consume far less disk space than a raster image. And second, a vector file can be more easily edited than a raster image -- whereas the latter can only be edited one pixel at a time, a CAD software program can be used to efficiently and effectively manipulate the database of vectorized representations of geometric entitites comprising a drawing.
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CAD Conversion

Standard Parameters and Assumptions Used in Vectorizing a Drawing

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