Discover the secrets of global origin.Excerpted from an article by Rick DeWitt, posted on http://AxiomInt.com. To get a copy of the full article series, please call 727-442-7774 extension 2225 or e-mail 2225@AxiomInt.com.In the many years I have worked with CAD professionals, one area that seems to be consistently misunderstood is "global origin". What exactly is it? What happens if you change it? How do you change it? How does it affect reference files?So let's clear the air in this article by starting with exactly what the global origin is and give some explanation of how it is used. The "global origin" of a MicroStation design file (V7) or model (V8) is a setting which defines where, relative to the MicroStation design plane (2D) or cube (3D), the point where X=0, Y=0 and, for 3D files, Z=0 is located.It helps when visualizing this concept to think of the MicroStation 2D design plane as a big piece of paper and the global origin as a point on this big piece of paper that we refer to as X=0 and Y=0 in the coordinate system. Although you could put the global origin outside of the piece of paper, we'll assume, for this example, it's on the paper. You could set the global origin point, as one example, to be the lower left-hand corner of our piece of paper. (See Figure 1.) If we decided to set our MicroStation design plane with this global origin setting then all the elements we draw on the design would have to have positive X and Y coordinate values because we are not allowed to draw elements outside the piece of paper.If we set our global origin to be in the middle of our piece of paper then we would have the ability to draw using both the positive and negative X and Y axis directions. However, if you set the global origin as the lower left-hand corner of a 2D design plane, then all of your drawing coordinates will be positive numbers.So what's all the fuss about global origins? Why not just set the global origin in the center of the design plane or cube for every drawing and get to work? Well, for example, one of the main reasons for difficulties with global origins stems from the fact that, in MicroStation versions prior to V8, the design plane wasn't big enough for many users' needs. To solve this problem, many companies and government entities developed CAD standards that demanded the use of a global origin that was located far away from the center of the design plane and still insist on this location today, in order to remain compatible with older (pre-V8) designs.Prior to V8, the design plane was limited to a set number of accessible points on each axis. For many MicroStation users, this size was sufficient. However, for civil designs that use real-world coordinates, the number of feet required can easily exceed the limited number of points. So, for these users, setting the global origin outside the design plane was the only way they could place design elements on the design plane when drawing to locations that required large coordinate values.Example: A road to be built in Oregon has to be drawn using exact locations. In the United States, one common standard requires that geographic locations be represented by the number of feet that a location is to the east and to the north of a specific point (which point is also defined in the standard). In parts of Oregon, the X coordinate (based on this geographic standard) can be in the neighborhood of 4,298,000 feet from that fixed point. Therefore, when attempting to draw a road at this location in MicroStation V7, users had to have the global origin well off the design plane in order to draw their road at the correct "real-world" geographic coordinate point.Fortunately, as of MicroStation V8, the size of the design plane is now greatly expanded. But even with this increase, many CAD standards still require global origin settings that match those of the earlier pre-V8 design files when the design plane was smaller. This fact alone frequently causes confusion when other companies (that don't still have this old requirement) create design files that are not based on this CAD standard. However, there are solutions to these issues.
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In the many years I have worked with CAD professionals, one area that seems to be consistently misunderstood is "global origin". What exactly is it? What happens if you change it? How do you change it? How does it affect reference files?
Get More Information or a Free Demo For more information on global origins, to get the entire article series or to schedule a free, online demonstration about handling issues regarding global origins, call 727-442-7774 extension 2224, e-mail 2224@AxiomInt.com or visit Axiom on the Web at http://AxiomInt.com.727-442-7774 extension 2224, e-mail 2224@AxiomInt.com or visit Axiom on the Web at http://AxiomInt.com. Get a Unique Version of this Article Article Spinner
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