Original Article Date: March 14, 1999
Need to convert a metric file to imperial, or vice-versa in MicroStation V7? This article explores the mathematics behind doing such conversions and should be read before setting up any project where converting files may become a possibility. It will also help you understand what working units are all about.
Authors Note: Portions of this article have appeared in the May 2000 issue of The MicroStation Manager Magazine
Did ya know that if you set up your working units correctly you can easily convert your files from imperial to metric without affecting the size of your elements in the design!!!
If your imperial file has working units set to: 1 ft : 12 in/ft : 2032 pu's/in then the metric version of this file would be: 1 m : 100 cm/m : 800 pu's/cm
Let's take a closer look at the math:
The master units ft we'll change to an m for meters. And the sub units of in will be changed to cm for centimeters. So far so good!
Since we know that there are 2.54 centimeters/inch, we simply divide our 2032 pu's/in by 2.54 to get the number of positional units per centimeter. In this example the final result is 1 m : 100 cm/m : 800 pu's/cm. Can't get any easier than that!
The following table shows some popular "pairs" of working units that can be used to switch your files from imperial to metric without the loss of accuracy. Note that in each case, we're simply dividing the pu's/inch by 2.54 to get the equivalent pu's/cm.
Common Pairs of Working Units
1 : 12 : 2032
1 : 100 : 800
1 : 12 : 1016
1 : 100 : 400
1 : 12 : 508
1 : 100 : 200
1 : 12 : 254
1 : 100 : 100
In the situation where imperial files are set up using 1ft :12 in/ft : 8000 pu's as the working units, be advised that there isn't a true metric equivalent for these units. Let's take a closer look:
The master units can be changed from 1 ft to 1 m easily enough, and you can also re-define the sub units from 12 in/ft to 100 cm/m without a problem. But what happens when you divide the 8000 pu's/in by 2.54? You get a value of 314.96062! Now what? Well, you could just round this value up to 315 so that your final working units become 1 m: 100 cm/m : 315 pu's/cm but since this is not a "true conversion", accuracy may become an issue.
As you can see, it's no problem to take files back and forth from imperial to metric and vice-versa without comprimising the integrity of your data. Just be sure that the number of imperial positional units are equally divisible by the metric conversion factor. It's just that easy!
AskInga Article #30