Part two in a series of articles on the mysteries of global origin
By Rick Dewitt
Have you ever started a project and noticed that one or more reference files didn’t seem to line up in your master files the way you expected or that the geometry you expected to be a particular size was too big or too small? In a previous issue of MicroStation Today, I wrote the first segment of an in-depth discussion on the frequently misunderstood subject of “global origins”. [Editor's note: See MicroStation Today Volume 16, Issue 3. The article can be found here] Not understanding global origin and a closely related topic, “working resolution”, can lead to a host of questions such as:
Not knowing how global origin affects your design files could result in time-consuming and costly mistakes — the kind that keep you up at night.
- What exactly is the global origin?
- What happens if you change it?
- How do you change it?
- How does it affect reference files?
- How is working resolution related?
- Does Axiom have any products that can help fix global origin and working resolution problems?
In this article, I will continue that discussion so you have an even better grasp of the subject, how it can impact your projects and what you can do if you discover the global origin is wrong in some or all your project design files.
If you ever had a time when one or more reference files didn’t line up in your master files the way you expected after attachment or the geometry appeared way too big or way too small, then you had mismatched global origin settings, working unit settings, working resolution settings or some combination of all three.
The global origin is a setting made relative to the MicroStation design plane (for 2D) or cube (for 3D) which defines where the x=0, y=0 and z=0 coordinate point is located. The global origin point, when you ask MicroStation, is defined (set) as a certain number of master units (like feet or meters) from a predefined fixed point on the design plane (or cube) along each axis. The “predefined fixed point” is set by Bentley (more on this below).
“Master units”, as you probably know, define what we will call the real world distance measurement in a design file.
For civil engineering projects, this is usually feet or meters. If you are designing circuit boards however, you would probably prefer inches or millimeters as a master unit.
“Working resolution” defines how many units of resolution are going to be used to make up a specific unit of measure like a foot or a meter. For example, if you set the units of resolution to 1,000 units per foot in a design file, then a line that is one foot long will take up ten times more design plane than a one-foot line in a design file whose units of resolution are set to 100 units per foot. So, if you attach a reference file that uses 1,000 units of resolution per foot to a master file that uses 100 units of resolution per foot, at a scale of 1.0, then a one-foot line in the reference file will look like a ten-foot line in the master file.
Because the global origin is expressed as a value in master units like feet or meters, the same point on the design plane can have a very different value when the master units of two files are different or the working resolution is different for the same distance of measure.
Combining V7 and V8 files can create unexpected problems.
In MicroStation V8, the predefined fixed point used to help locate the global origin was changed from where this point was in V7. Specifically, the predefined fixed point was moved from the lower, left-hand corner (for 2D designs) to the exact center of the design plane. What’s more, the design plane is significantly larger (about 2 million times larger) in V8 than it was in V7. For 3D designs, the predefined fixed point was moved from the lower, bottom-left corner (where it was in V7) to the precise middle of the design cube (in V8). This change has created some confusions and problems — particularly when combining MicroStation V7 design files with MicroStation V8 design files in the same project.
One example of such problems occurs with “coincident” reference file attachments. When you make a coincident reference file attachment, MicroStation orients the two design files so the design planes match up exactly. It’s important to know that the thing MicroStation matches up is the design planes, not the global origins. In projects where all the design files (including all the reference files) use the same global origin and the same working resolution, then obviously all the global origins and geometry will happen to line up as well. Unfortunately, this is not the case if the global origin or working resolution settings of a master file are different from those of an attached reference file. In this case, the geometry in the reference files will not line up as expected due to global origin differences or the size of the elements will be wrong due to differences in working resolution.
When the global origins are different between master and reference files, a coincident attachment will offset geometry just like the global origins are offset above.
For instance, let’s say that you have a hybrid project that includes V7 design files, V8 design files and maybe even AutoCAD files. If each type (V7 or V8) of MicroStation file uses a different global origin setting and the working resolution settings are different, you are going to notice reference file geometry not having the expected orientation to the master file’s coordinate system. Also, the size of the geometry from the reference file will appear wrong.
Similar to the above, if the V7 or AutoCAD files are being translated into V8 format or vice-versa, you can easily run into the same problems if the translators are not set up to handle these factors properly. Understanding global origin and working resolution and how to fix them is crucial when you are responsible for creating projects that must comply to CAD standards or if you have to define the CAD standards others must follow.
Avoiding a time-consuming nightmare
Let’s say you translate a group of files from AutoCAD to MicroStation V8 without ensuring that the translated files come into MicroStation with the required working units (such as feet or meters), resolution settings and global origin settings. Guess what? You are playing Russian roulette with your company’s potential profit on that project. It’s true you might get lucky using the default translation settings or you might have a client who isn’t picky about settings as long as the sheets plot correctly. But if you aren’t lucky and the project has to be fixed to comply with a different resolution standard and a different global origin value, you will have a time-consuming nightmare on your hands. Why? Because changing the resolution changes the “real-world” size and location of every element already in the design file and changing the global origin changes the coordinate location of every element. To get things right after designing the project, you will have to re-scale and move everything. Re-scaling and moving elements obviously affects where reference file elements are going to display in master files. If reference file attachments are clipped, the elements in the reference files, after being rescaled and moved, will almost certainly disappear outside the clipping boundary, making it necessary to fix that as well. I could go on but I’m sure you get the point.
Some solutions may not meet your CAD standards.
In MicroStation V8, Bentley added a new attachment method called “Coincident World” to help make this all a little easier for users to deal with. “Coincident World” matches the attachment’s global origin to the master file’s global origin. This is really useful when files from multiple projects — that may have different global origin settings — are used together. Using this attachment method along with the “True Scale” option (which automatically scales the attachment to compensate for differences in working units or resolution) can make combining files from different projects very simple in V8 — provided you don’t have CAD standards that forbid having different global origin settings or different working resolution settings. Unfortunately for many, a number of CAD standards still require the use of very specific global origin and working resolution settings. When those settings aren’t followed, the time-consuming nightmare mentioned above comes into play.
Because of these problems, Axiom added additional features to Global File Changer that help isolate design files with non-standard settings and provide a way to easily update those design file settings to match the standard. Global File Changer and other tools from the MicroStation Productivity Toolkit provide effective solutions that can drastically reduce the time required to fix project design files, including those created using non-standard working resolution or global origins settings.