The I/RAS B raster editing products and vector-based MicroStation use different measurement systems. Which system should you use?
The I/RAS B measurement system performs calculations in either raster inches or raster centimeters. The raster dimensions are based on the original dimensions of the scanned document. Users often use the I/RAS B Measurement command to establish the size of speckle removal or to determine the thickness of a raster line.
The measurement system of MicroStation's vector environment uses Units of Resolution (UOR's). Measurements are calculated based on an arbitrary system of units and sub units. You can specify the units and sub units and the relationships between them. For example, you specify a system of fathoms and feet, indicating that 1 fathom = 6 feet.
However, even if you specify MicroStation units as inches and centimeters, the MicroStation and I/RAS B measurement systems do not interact with each other.
To find the measurements of an image area composed of both raster and vector elements, use the MicroStation Measurement command. As a result, depending on how the raster drawing is placed relative to the design file, a raster drawing that measures 34 inches wide in I/RAS B may represent only 0.1 inch in MicroStation.
You can position your raster drawing in the design file so that raster inches correspond to design inches.
Use the I/RAS B placement command (View - Placement - By Rectangle) to position the drawing. Assume that you have a scanned raster drawing that, in the preview screen is 30 inches by 40 inches. With this information and the original scale of the drawing, you can place the drawing in the design plane so that raster inches and vector inches match.
A good test for proper full-scale placement is to measure a dimensional area of the scaled raster drawing (such as a line that is marked 50 feet) with the MicroStation vector measuring tools. These raster and vector inches should now match.
Of course there are other ways to achieve the same result. One way involves placing a vector block with the correct scaled measurements and using tentative snaps to place the raster. Another method involves the use of "dx" or "di". Of course, raster data should be placed so it is most useful to the specific workflow. If working full size is necessary, then raster placement is the answer.
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