Plotting rasters

Original Article Date:  Feb 5, 2001

A few things to know about plotting Raster Images from MicroStation V7.

Printing on your system printer…some considerations:
In order to reduce the amount of time it may take to spool the drawing to the system printer, and to keep the file size to a minimum, create a print file (filename.prn) and copy it to the printer. Specific steps for Windows NT are as follows:

To set up printer and port:

• Create a new printer where it's property has been set to File instead of a specific port. This is done via
  Control Panel > Printers > Add Printer.. Ensure that the correct print driver is selected.
• Create a port connection to the printer using the net use command: NET USE [devicename] [\\computername\sharename]
  For example: NET USE LPT3 \\PRINTMAN\HP650C will return the message "command completed successfully" and set \\PRINTMAN\HP650C as the destination of the LPT3 port for that machine.

In MicrcStation:

• Send the file to print using:Print > Page Setup > Select modified/new printer > Print > Enter print file name (filename.prn). This will create a file using the printer intstructions to disk.
• To send print file to printer, pop to the system command prompt and keyin: copy filename.prn ltp3: /b

IMAGE PLOTTING from MicroStation when using Raster Reference Files:
When plotting raster images, use the HPGLRTL.plt for best results. PostScript drivers (PS650C.plt, PSC650C.plt, PSCRIPT.plt, PSCRIPTC.plt) also give quality image output, but can create large plot files. These files are not limited to just image plotting, as they will plot vector data with high quality also. HPGL2 drivers (HPDJET.plt and HP650C.plt) plot vector data very well, but images plotted with the HPGL2 drivers will be grainy and may result in large plot files. HPLJET4V.plt and HPPCL5.plt will produce quality image output.

Note:
Images will not plot correctly with any driver unless the hardware_raster/resolution=300 line in the .plt file is un-commented. This is done by removing the semi-colon (;) at the beginning of the line. The wording of this line may vary slightly in some files (i.e. software_raster/resolution=32).

IMAGE PLOTTING from Image Manager or DESCARTES:
MicroStations Image Manager supports PostScript and HPGL2/RTL devices, as well as all raster devices supported through the Windows Print Manager. The Image Manager will allow you plot to the following devices:

• PostScript plotters
• HPGL2/RTL plotters
• Other supported plotters ("generic" plotters)
• Your system printer

MicroStation's plot driver file creates the vector data portion of the plotfile in filename.000. Image Manager's driver creates the raster data portions in a HMR0 file. The resulting composite plotfile (filename.000) includes information about both the vector data and raster data of your image.

Four sample plot drivers are delivered with MicroStation / Descartes:

Where: “im” = MicroStations Image Manager and “dc” = Descartes in the above table.

Settings in the various plotting dialog boxes let you control the output to the respective plotters, or printers. (File > Print/Plot > Setup > Device)

Plot Raster Images
This parameter, which is saved with the project, enables or disables the plotting of raster images. It’s ‘on’ by default.

Gray Scale
RTL - Turn on to use Gray Scale to plot images in gray scale RTL format even if they are color images. If you wish to print color images, and your RTL device supports color, leave Gray Scale turned OFF.

PostScript - If Gray Scale is ON, images are plotted with a half-toning technique that renders shades of gray. Leave it turned OFF to plot images in color PostScript format.

For both RTL and PostScript devices, the following also applies: When plotting to a black and white RTL or PostScript device, you should turn on Gray Scale, even for color images. This saves time and minimizes the disk space required to plot the image.

Color mosaics of multiple images can be printed correctly even though they may not display correctly on your monitor. This can occur because each image in a view is plotted to a color PostScript device using its own color table, like with a 24 bit display. (If you have an 8 bit display and one image is active, all images use its color table for on-screen display.

The ON/OFF status of the Gray Scale option does not affect the design files. Therefore, you can print color design elements in a color PostScript format even if the Gray Scale check button is ON (to plot the images in gray scale).

Use Fence
Used to indicate whether the raster images should be clipped to the fence when plotting the view. The Use Fence option is only available when a fence is active.

Contrast and Brightness Settings
Used to set the contrast and the brightness of images in your plots. These settings apply only to images when plotting. They do not affect the on-screen display of images.

Output Resolution
It is recommended that you select the maximum possible number of pixels per inch for the output resolution. You can use a lower resolution to obtain a quick draft output but the higher resolution should be used to obtain high quality output.

To ensure maximum quality for your plot, you should set this value to the same resolution as that of your printing/plotting device. With devices that use half-toning, however, the maximum resolution that you can achieve is the net resolution after half-toning (that is, the net resolution will be less that the overall resolution of the device). Since a value set higher than necessary usually does not provide added resolution, it is advisable to determine the optimum value to minimize the size of your plot file.

To calculate the output resolution that will produce the smallest plot file size:

1. Determine the net resolution of your device. This value should be less than the resolution of the printer. The Image Manager default value is 80, since it is the typical net resolution for 300 dpi printers that plot in gray scale with half-toning.
2. Optimize your plot file size by determining whether your plot requires the full available resolution. Use the following formula to optimize the plot file size:
   (Image Width/Pixel Size) / Width of Plot = Optimal Resolution
   For example, if the image width is 1000 meters, the pixel size is 1 meter, and the width of the plot is 5 inches, then: (1000/1) / 5 = 200 dpi

Note: Use the Image Location Editor dialog box to find the pixel size and the image dimensions (see Image Location Editor dialog box ). In this example, the maximum quality output can be achieved with a resolution set at 200 dpi. Consider also:

• Any higher value creates a larger plot file, but does not increase quality.
• If the net (true) resolution of your device is lower than 200 dpi, then any value higher than the true resolution also creates a larger plot file, but does not increase quality.

In this instance, if your device does not contain the true resolution necessary to achieve the maximum possible resolution inherent in your image, then your plot quality cannot be maximized. After the Maximum Resolution is set, the Output Size of Raster Data field displays the amount of raster data that will be created. The total size of the PostScript file also includes the vector data.

Plotting Design 87 and 88 Elements
Key-ins can be used to enable or disable the plotting of Design raster element types 87 and 88 when using the Plot feature.
To turn on this feature keyin IMGMANAGER PLOT8788 SETON

When the toggle is set to ON, MicroStation plots type 87 and 88 elements with the same options used to print raster files (clipping to the fence extent, converting to gray scale, and so forth).
To turn off this feature keyin IMGMANAGER PLOT8788 SETOFF

RTL Plotting - Exceeding Installed Memory on Plotter
If you are not using the Print Manager to plot files, it may happen that the raster portion of the plot does not fit entirely into the plotter's memory. When this happens, several options are available:

• Add more memory to the plotter.
• Reduce the size of the plot file by reducing the resolution or paper size.
• Use the Plot On The Fly Feature.

The Plot On The Fly feature is activated by inserting a special keyword into your plt file. When this keyword is found, MicroStation generates the plot file in such way that when the plotter's memory is full, it:

• Stops input of data.
• Starts the drawing.
• Starts input and plotting of data one band at a time until it reaches the end of the file.

This method is slower but allows plotting large raster files on a plotter with minimal memory installed.
The only condition to use this feature is for the design file to entirely fit into the plotter's memory. Conventional ways require the raster data be spooled first and then the vector data (design file). When using Plot On The Fly, the vector data is spooled first. This method ensures that no matter how large the raster portion is, it will never outrun the plotter's memory.

Warning: Using Plot On The Fly always produces translucent vectors. Vector information will be transparent and some colors, like yellow, may not show properly when an aerial photograph is beneath the vector data.

AskInga Article #42