This Client Server article is republished in its entirety from 2002 for reference purposes.
By Bentley Technical Support Group05 August 2002
Ensuring your raster modifications stay within the URB will help maintain a seamless workflow and improve your productivity.
Borders are used in all manners of our lives, from wallpaper to engineering drawings. Borders are also boundaries; they define the extents and limitations of our lives and plans. This article explains how MicroStation I/RAS B, Bentley's binary raster editing, cleanup and vectorization solution, uses borders. It will also offer ways to help you stay within the borders or ways to move back should you cross over.
There are two types of borders in MicroStation I/RAS B. The first border, a dashed line, is the image border. This border, when turned on, is useful because it shows the current size of the raster data, the extent of the raster data if modified and the position of the raster file relative to the MicroStation vector data.
Figure 1. Example of raster image and image border.
Figure 2. Example of raster image, image border and ultimate raster borders.
Each raster file opened within MicroStation I/RAS B is referred to as a layer. Each layer is assigned a color as determined by the user and the display color table being used within MicroStation. Along with the image color, the image border is also displayed using the same color. For example, if the raster layer is red, the borders will also be red. Figure 1 shows a typical MicroStation I/RAS B raster image and dashed image border.
The second border in MicroStation I/RAS B is the Ultimate Raster Border (URB), represented by a solid-line border. The URB determines the total extent of raster data that can be placed on any particular layer. Many times, in order to see this border, the raster image view must be zoomed out until the solid-line border is visible. Figure 2 shows an example.
Often, a typical user of MicroStation I/RAS B is unaware of this border and its affect on raster data. The main issue regarding the ultimate raster border is that no modifications or cleanup on a raster file can occur outside of it. This can cause confusion and loss of production time if you are not aware of the URB.
For example, it is impossible to warp a raster image so that the raster data goes outside the URB. Whether it is a simple Helmert warp trying to edge-match two files together, or a First Order Affine warp where the end result should be raster data inside a vector block, the URB must be acknowledged. In both of these scenarios, if the raster data eventually ends up outside of the URB, nothing will occur. Another example would be trying to use the move or copy commands. The URB will not allow any raster data outside the border. (See Figure 3.)
Figure 3. Trying to warp or move a raster image outside the URB to a vector block will give no results. Production time can be wasted if the user spends time trying to modify raster data that simply will not be warped, copied or moved in violation of the URB. It's an easy thing to overlook, and more common than many realize.
While the URB can be a stumbling block if overlooked, there are easy work-arounds. The URB is based on two variables. Modify these variables and you modify the size of the URB. The variables are IRASB_MAX_X and IRASB_MAX_SCAN, both located in the irasb.cfg file. By default, the URB is 65,000 scan lines in both the X and Y directions. If you need a larger border, you can increase the value of each variable.
But there is a better way. Place the raster file correctly using the Interactive Placement by Rectangle option when first loading the raster image. This function is located on the MicroStation I/RAS B Load dialog (Figure 4). The URB is calculated by the center origin of the raster image, outwardly, in both the X and Y directions.
Figure 4. Interactive placement by rectangle in lieu of use raster file header transformation. When using Interactive Placement by Rectangle to place a raster image, the location at which you place the image in the design file will always result in the X and Y directions correlating to the IRASB_MAX_X and IRASB_MAX_SCAN variables. Whether your raster image is the size of a postage stamp or in real-world units, the above variables control how many scan lines are set in both the X and Y directions, making your URB larger or smaller on the design plane, depending upon the raster image placement size in the design file.
To return to the situation depicted in Figure 3, if you need to move the raster image beyond the URB to a vector border, it would be appropriate to use the View > Placement > By Rectangle command, repositioning the raster image closer to the vector border, thus creating a larger URB area.
Ensuring your raster modifications stay within the URB-which includes recognizing the separate URBs for each individual layer-will maintain a seamless workflow and improve your productivity.
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