Original Article Date: June 5, 2003
Edited Date: May 22, 2009
Specifically written for folks doing maps in the northern hemisphere, this article discusses how you can set up the Global Origin correctly in MicroStation V7 and avoid using a false northing.
Below is a representation of the typical 2 dimensional design plane showing the global origin (XY=0,0) in the center.
For most purposes the Global Origin is fine where it is, however when working with maps it is sometimes necessary to shift this origin in order to accommodate very large UTM values where eastings and northings are expressed in meters.
Let's assume that your mapping project is based on a UTM projection and your coordinates are something like 320,000mE and 6,200,000mN. For this example, we'll also use the following working units: 1m:100cm:10pu or 1m:1000mm:1pu.
If you were to use the delivered seed files the location of the global origin would restrict your maximum northing to be 2,147,483.648 meters as shown in the following image:
One common method for overcoming this restriction is to subtract five million off your northing so an element would be placed at XY=320000,1200000 instead of XY=320000,6200000. Another solution is to change your working units to increase your working area.
Although both methods do work and are quite manageable, they have their drawbacks. By using a false northing, all incoming data will need to be modified, and by changing your working units you may be sacrificing accuracy for the sake of location.
Note: The following information deals with moving the global origin. If you're not familiar with the global origin, please refer to Understanding the Global Origin.
In MicroStation V7, you can re-position the global origin with this keyin:
In MicroStation V8i, you can re-position the global orign with this keyin:
The Y value of the V7 keyin above is calculated by taking your ‘false northing' and subtracting 2147483.6480 from it. This change to the global origin can be done to existing files without having to re-position or scale them.
For new files use GO=0,5000000 followed by a reset. This will assign those coordinates to the design plane origin and give you tons of space for placing your elements.
When working with the GO= command, note that it's a savable setting you must save your settings for the changes to be retained. If you've made a mistake, you can exit the file without saving the settings and then go back and try again.(Disregard the page numbers below...there is only one page to this article...thanks!)
AskInga Article #38