Using AutoCAD's Raster File Formats Plotter Driver to Create TIFF files.

Introduction

The new format for plans in the Saskatchewan Land Titles System is TIFF using CCITT Group 4 (2D) compression. AutoCAD (versions 2000 or newer) will create this file from a drawing, with a little massaging. This also may work for R14, but I haven't tried it.

AutoCAD actually can only create files at 100 dpi (dots per inch). The minimum resolution needed is 200 dpi which is FAX quality. Ideally the minimum resolution should be 300 with higher quality preferable. The limit here of course is the size of the file. The better the quality (more dpi), the larger the file. 300 dpi is a good compromise.

While AutoCAD can only create the file at 100 dpi, there is a way to get a 300 dpi or better file using other software to convert the plotted drawing.  The examples I give here will use 300 dpi as the target and use the Imaging software that comes with Windows 2000 to do the conversion.

The benefits of creating a TIFF file directly is a better quality product, the plan is never scanned, and you can email the drawing to ISC rather than using Canada Post.

Adding a TIFF Plotter

AutoCAD supports what it calls Raster File Formats. One of the supported raster file formats is TIFF with CCITT Group 4 (2D) compression (or uncompressed). To add the plotter, select File->Plotter Manager and use the Add-A-Plotter Wizard. In the Wizard, select My Computer, then the Next button to display the available models. Under the Manufacturers select Raster File Formats. Under Models, select TIFF Version 6 (CCITT G4 2D Compression). Click the Next button and accept the defaults until you get to the Plotter Name page. If you're satisfied this the default name, then click Next to get to the final page of the Wizard.

On the final Page, click the Edit Plotter Configuration button. The only thing you need to change here is the resolution and color. Select the Device and Document Setting tab and then double click the Graphics option to expand it. Click on the Vector Graphics item. The option should appear on the bottom of the page. You will want to select Monochrome and 2 shades of gray. Note that there is only one resolution (100 dpi) available. Click the OK button, and then Finish in the Wizard.

This creates the TIFF Plotter driver.

Plotting to a TIFF file

Plot the drawing as you normally would. On the Plot Device tab, select the TIFF Version 6 (CCITT G4 2D Compression) plotter that you created above. You should note that the Plot to File option is selected by default and you can fill in a name and location for the file that will be output. The defaults use the drawing name.

Just as you normally would, you will have to specify the page size that you want to plot to. The page size is going to be specified in pixels. No that's not some sort of fairy dust, a pixel is another name for dots or the unit of measure for raster file formats. If you remember, our desired resolution was 300 dpi or 118 dpcm (dots per centimetre). That means that the page size will be inches x 300 or cm x 118. For this example let's use a standard ANSI B (11x17 inches) as the final product. the size in pixels will be 3300 (11 * 300) x 5100 (17 * 300) pixels. In metric the calculations would be 3297 (11*2.54*118) x 5095 (17*2.54*118) so if you round them up to the nearest 100 pixels, it's the same thing (in pixels).

To create this page size, click the Properties button and then select the Custom Paper Sizes item. Click the Add button to Add a new paper size, and use the Wizard to create a page 3300 x 5100 pixels.

On the Plot Setting tab select the options as you normally would. You will have to convert your scale to pixels = drawing units. At 300 dpi, there are 118 dots per centimetre (300 / 2.54) or 11.8 per millimetre. If your scale is 1:1000 then it will be plotted 1 mm = 1 metre or in our case 11.8 pixels = 1 drawing unit. 1:2000 is 11.8 pixels = 2 drawing units and so on.

Then just click OK to plot. A tiff file will be created of your plotted drawing. You can use Windows Imaging to view the file, but because of the limitations of this program some larger sizes will not load. Imaging also shows metric files as negatives (white on black instead of black on white). However, for most cases, Imaging will work just fine.

The Caveat

Something you will notice about your drawing. It is 100 dots per inch and of course too course to be of any use. This is a limitation of the AutoCAD driver as described in Introduction. The other thing is that if you plot it actual size, it's three times the size it should be. There is a fix. What you need to do is convert the file to three times the resolution and 1/3 the size.

When you resample the file at three times the resolution and 1/3 the size, nothing is really changed in the bitmap. The file is identical in size as it was previously. At most, a few variables get changed. 

One thing that you have to remember when you plot the file three time the normal size, is that the line widths will be 1/3 the normal thickness when you scale it back down. The standard AutoCAD stroke fonts are also affected. The truetype fonts are not affected. If you use the default line thickness, you should change it to 0.60 mm or something similar. You can change the line thickness in the layer dialog or use plot styles. I suggest using Plot Styles so that if you plot it on another plotter, you just have to use a different plot style to get it to plot correctly without having to change the line thickness in your drawing. You'll have to experiment to get it to suit your preferences.

Re-sampling from 100 dpi to 300 dpi

Personally I use Corel PHOTO-PAINT to resample (convert) the file, but most bit map manipulation programs can do the same thing. While Windows Imaging has some limitations, I'll use it as an example here because it comes free with Windows. This example uses Windows 2000 Imaging. Other versions may not work the same. 

To resample the file, open the file with Imaging. Under the Edit Menu, select Copy Page to copy the file to the clip board. Under the File menu select the New item. Under Compression tab of the dialog that comes up select CCITT Group 4 (2d) Fax. Under Resolution select 300 x 300 dpi. Click OK to create the new file. The Size doesn't matter if you are using Windows 2000 or better. It is automatically sized to fit your drawing. 

Under the Edit menu click Paste. If the program complains that the image in the clipboard is larger, just click Yes to resize (Windows 2000 or better). Check the Properties item under the Page menu to see that your drawing is now the proper size and 300 dpi. Save your new TIFF file.