| Applies To | |||
| Product(s): | AECOsim Building Designer | ||
| Version(s): | 08.11.09.nnn | ||
| Environment: | N/A | ||
| Area: | Settings/Attributes | ||
| Subarea: | N/A | ||
| Original Author: | Marc Thomas | ||
Problem
I read an article on Be Communities that mentions how changing the size of the Solids Working Area inversely changes the resolution, and the potential consequences from doing so. At what resolution would it begin to cause problems with AECOsim Building Designer? For example, using a Solids Working Area of 1000Km provides a Solids Accuracy of 1E-005 meters or 1/100 mm. Would this be OK? Does it matter if I'm modeling within or outside the SWA in this case? The project we are working on is a high speed railway about 600km in length where we will be doing solid modeling at many different locations for stations, bridges and tunnels, so using a single seed file with the same coordinate origin would be best.
Solution
Unfortunately there is no one-specific resolution value at which potential precision issues may become evident. For example, from a solids modeling perspective you may be able to successfully place orthogonally oriented rectangular slabs large distances from the SWA. But when adding complex fillets or b-spline cuts, the chances for precision errors in Parasolid bodies increases drastically. The same goes for processes such as Drawing Extraction where the viewing angle can make a difference as to what type of geometry is generated – lines and arcs, or complex surfaces.
The case above mentions a Solids Accuracy value of 100/mm is approximately 233 times less than what we deliver with AECOsim Building Designer (4.29E-005mm). But that delivered accuracy is based on the premise that a building is being modeled, which may include any number of complex facades and curved geometry. So the nature of that geometry and any post-processing performed can be an indication of whether the potential for precision issues exists.
In regards to the overall size of the project, it’s recommended to divide the entire structure into separate DGN files and reference them together using Geo Coordination. That allows each individual model to utilize the best level of accuracy available by remaining in or near the SWA while also maintaining the required coordinates. The size of each “portion” would determine how much falls outside the SWA and by what distance. An element typically needs to be some distance from the SWA to introduce any level of precision loss, though there is no means to predict the end result. One aspect to remember though, is that this potential is typically only relevant for elements and processes that use the Parasolid modeling engine – that is the "Solids Modeling Accuracy" referred to in the Design File Settings dialog.
In summary: A 1000Km SWA is larger than the entire railway which would of course allow it to fit in one DGN file. However, that comes at the expense of less precision. It would be best to use a higher level of Solids Accuracy just to avoid any chance of encountering precision related limitations later in the design process, which can be very difficult to reverse. The ideal scenario would be something in the range of what we deliver in AECOsim Building Designer, which is what Bentley develops and tests against. It requires some planning as to what goes into each file and who manages the overall layout, but from a design aspect it is a much better (and safer) approach.
Recommendations:
When modelling buildings with AECOsim Building Designer always use the default resolution of 1000 UOR/mm (the imperial equivalent is 304800 UOR/foot) set in AECOsim Building Designer's seed files. This is what we test against and some dataset content relies upon this resolution.
Break projects down into portions that fit within the Solids Working Area, see Setting Up in the Real World or "Where do we model?" for background and more detail on this.
Use Geo-referencing to relate Building to Civil Engineering models.
See Also
External Links
Bentley Technical Support KnowledgeBase
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