There are two main types of drawing programs available for use on computers; those that are pixel based and those that are vector based. 

Vector based drawing programs like IntelliCAD, store lots of information about every entity drawn. For example, a line is recorded in the drawing database as a line entity (i.e. the program knows that the entity drawn is a line) plus the co-ordinates for the start and end point of the line to an accuracy of 16 decimal places (floating point arithmetic), the layer on which the entity resides, its colour etc.. Similarly, if a circle has been inserted into a drawing, the co-ordinate of the centre of a circle and the length of its radius are recorded.

On the other hand, pixel based drawing programs (e.g. Paint - a version of which is supplied with every copy of Windows and MacPaint (the Macintosh drawing program) have a drawing database which simply records whether or not a dot on the screen is turned on or off.  This dot is called a pixel, a contraction of the words "picture" and "element". A line for example, is recorded as a series of lit pixels adjacent to one another. A pixel based drawing program does not know that you intended to draw a line, it simply records a row of pixels that are lit.

pixel images are often called raster images.

CADian IntelliCAD Professional is capable of displaying both types of images creating a hybrid view. We see both raster and vector information as shown in the figure below.

Typical hybrid image with raster (scanned) information at top and vector information below.

This facility is particularly useful where a company has a store of old paper drawings and only part of the drawing needs modification or where you might wish to take photographs of a site and combine these with vector information showing a new design for the site.

If you want to use the base raster information and write over part of it, it is a simple matter to use a pixel based photo editor to rub out old information from the original image and then reload it. We favour using Paint Shop Pro, but any pixel editing program can do this.

Tip do not use the software that comes with your scanner for photo editing, use a professional image editor - Paint Shop Pro, GIMP, or Photoshop.

Preparing your raster image

Raster images can come from many sources and can be in a variety of file formats. 

We favour a system where you store the master information in as high a format as possible, using the TIFF file format - an uncompressed image format. 

TIFF files can be produced by scanners so if for example, you commission a professional photographer to take photographs of a site for you, ask for the data to be delivered to you in digital format in TIFF file format (as well as conventional prints). The photographer may well take the photograph using conventional film and then use a drum scanner and software to create the TIFF file. These files will be large (commonly 20 Mb in size) so you need CD-ROM's for transport, a fast computer to manipulate them and plenty of RAM in your computer.

Flat bed scanners of the type normally found in offices do not produce images of the quality of drum bed scanners.

We then use our raster editing software and load the TIFF file and write out another (separate) file of appropriate image quality. For example, if we were producing web pages, then a JPEG file would be appropriate, but if we wanted a high resolution result in a CAD system such as IntelliCAD, then we would use a TIFF file. 

IntelliCAD Professional will accept .BMP (the native Windows format), .PCX (the PaintBrush format), .GIF, .JPEG and .TIFF files.

Some scanning bureaus use GROUP 4 fax format. While this is an efficient format in terms of file size, we prefer to convert to TIFF format.

Attaching raster images to CADian Professional

Start IntelliCAD. 

It is a good idea to create a rectangle of appropriate size and position ready as a base so that you can locate and scale the image appropriately.

You might put the rectangle on layer DEFPOINTS so that it does not print.

Now use the IEIMAGE command (or select the command from the toolbar or the drop down menu) and navigate to the location of your file. Select the file and import it. A raster image is treated just like a block, you will be asked for the insertion point and a scale factor. This is where your rectangle template comes in handy. 

In the example below, we wanted to work in tiled model space at a scale of 1:5 and using an A1 sheet to display the drawing. According to the Australian standard, an A1 sheet is 801mm wide by 566mm high so we inserted a rectangle on layer defpoints scaled by 5 (4005mm wide by 2830 wide). This is shown in red in the figure below. It was then a simple matter to attach the raster image, insert it at the lower left of the rectangle and scale it to the upper right. 

It is now a simple matter to use normal IntelliCAD commands to add vector (CAD) information over the raster image, to create the hybrid image.

It is a good idea to check the dimensions in the drawing and to draw a line equal in length to the dimensioned line to ensure that you have scaling correct.