Using Raster (Scanned) Images Within a CAD Drawing Environment

Q - How Can a Raster (Scanned Black & White) Image be used Within a CAD Drawing Environment?

A - One of the basic ways in which a raster image (e.g. image of an actual drawing) can be introduced into a CAD package is by importing it in its original graphical format and utilising it as if it were a photo. By doing this the user can plot/print the image with other CAD information on the drawing or actually add other CAD information on top of it. (Check that your CAD software will accept the - importing of a raster/graphic image)

• Use a graphic package to delete selected areas and then import the image into the CAD package for quick manipulation of a raster image on a drawing. Additional items can be added to the deleted areas (e.g. modifications/extensions to a building).
  
  
• Raster images can be brought back into their correct scale when imported into the CAD package using the software 'scaling' command normally found in the modify menu of commands.
  
  

Q - Is There a Quick Way to Convert a Raster Drawing Image Into a Workable CAD File - (Vectorisation)?

A - Yes, to help convert the raster drawing image into a CAD file there are a number of raster to vector conversion packages on the market.

• A Vector relates to each single drawing entity that makes up a drawing such as a line, arc, circle, etc.
  
• The raster to vector programs work by trying to identify where complete entities start and finish. By tracking the thousands of dots that may represent an entity (e.g. a line) on the raster drawing image and placing a single vector over the area tracked.
  
• The Vector image is usually converted to a .DXF/.DWG file format that can be read into most CAD software packages.
  
• The Vector file produced from the Raster image is then a proper CAD file that can be worked with normally.
  

Q - What is the Accuracy of the Raster to Vector Conversion?

A - The quality and accuracy first depends on the quality of the original paper image, and the resolution dpi (Dots Per Inch - normally 300 dpi for drawing work).

• All of the image will be converted. However, the percentage that will be useable can vary dramatically and it is most often the case that some manual CAD work will be required.
  
  
• Most Raster to Vector conversion programs also allow you to manually tidy up the Raster or Vector image with drawing tools for tracing over the image, or adding to it.
  

Q - Is There a Quick Way to Convert a Raster Text Image into a Workable Text File?

A - Yes, on the market there are a number of OCR (Optical Character Recognition)software packages that will help convert a Raster text image into text by automatically identifying letters/words.

• Like raster drawing vectorisation the accuracy of conversion depends upon the quality of the original paper image, and usually requires some modification by the user.