We are using Rhino/GH for developing some bridge geometry based on US Survey Feet unit. The 3dm file will eventually be attached and/or imported into Bentley OpenBridge Modeler (OBM).
The problem is that when we define the US Survey Feet Unit, as a custom Unit in Rhino, it seems like OBM understands the custom unit to be in meters.
When the model is defined using Feet (built-in unit), the geometry is imported correctly.
Is there a way of adding a built-in unit in Rhino for US Survey system? Or, is there an specific format for custom Units we should provide Bentley for fixing this issue?
If international feet are working for you, use that. Survey feet were obsoleted by NIST, see U.S. Survey Foot | NIST
The difference between both definitions is about 6 microns. I’m quite sure that does not matter for objects the size of a bridge?
Also, this quote from the NIST article:
The preferred measurement unit of length in the United States is the meter (m) and surveyors, map makers, and engineers are encouraged to adopt the SI for their work.
The custom unit may not be supported by OBM, or not in the way that you defined it. You need to contact their tech support for this. All the required information is in the 3dm file to be able to support it, but the OBM code needs to read it, and handle it correctly. Give them your 3dm file with custom unit, and point their developers to the file opennurbs_3dm_settings.cpp for all the information they need.
Thank you for your response but, we are required by contract to use US Survey Foot.
Our contractor will be survey and layout this large structures with complex geometry based on the very specific global North/East coordinates we define in our drawings. We want to define the 3D geometry of our bridges in the 3dm file, and then cut our 2D construction drawings from the 3D model.
In order to present our case that Rhino has enough precision to be implemented in the Infrastructure Industry, we think we need to show that we have the required units. Can McNeal consider including this unit as a default moving forward?
Let me summarize (and please correct me if I’m wrong)
importing works if you use the built-in Feet & Inches unit
survey feet is an outdated unit
the software (OBM) that fails to import a custom unit is not made by McNeel but by Bentley
If the above tracks, the chances of McNeel adding an outdated unit to Rhino are slim to none. My advice is to contact Bentley and tell them about this problem, with the request to properly support 3dm custom units. 3dm is an open format, they just need to read it correctly I think.
Great response, our company works in the architectural field and it is surprising how many of our customers do not know this. We make our customer state the whether their coordinates are in US survey feet or International feet or we will not process the project. Drawings are useless because they typically do not specify which units are used and we will not make the assumption.
The point is one cannot assume US Survey feet. When survey coordinates are provided, the units system must be specified. That is the responsibility of the party providing the coordinates.
NIST may have recommended to deprecated the US survey unit, but current projects are still being done using this unit. Yes, there are two options for this: International Foot and US Survey Foot, and each State, by State Law, defines which one they want to use.
Ok, I’m going to try to convince Bentley to accept Rhino custom units, but my expectations they will be accepting this request are close to zero.
As a workaround you could work in USFT custom units in Rhino and when ready change the 3dm file units to meters, using the preserve size option, in order to produce a file with units that can be imported to Bentley. If necessary you can flip the 3dm dimensions back to custom if you need to do more work on the file in Rhino. A quick test shows a 1000 USFT object will convert to 304.80060960m and back to 1000 USFT.
To explore the import issue further, when setting up your Custom Unit in Rhino what name are you giving it? Is this the same as Bentley use in their software? What name is used in a dwg file?
Some applications do not accept US Survey feet, so its not just Bentley. NavisWorks does not and it is widely used. The suggestion is to use Revit. Since you are using Bentley, that is useless and requires an inconvenient and possibly error prone work around to convert to units that Bentley can use.
I understand there is legacy survey data that is in US Survey feet, I don’t question that. However, the units system may not come along with the coordinates. You example image above does not state which coordinate system is used. Given 50 states, our company would not research every state and county to find out the correct units because the units may vary even within a state. We are not surveyors and rely on the units system used with the coordinates to be provided to us.
In the 1970s and we were told in middle school to learn metric, as we would need it as adults. 50 year later only ones using the metric system now in the US are in the sciences. There are only 3 countries in the world that do not use the metric system widely, and one of them is the US. That is ridiculous. Sorry for the rant.
Much of U.S. industry uses metric as the primary unit system. The automotive industry was fully converted to metric before 1983 (when I started working in it).
Canada is “fully metric” except there is still considerable use of “imperial” units.
