CAD users who work with complex 3D models all face the same problem: it can take a long time to load large geometric models into their systems. As a result, users may wait for some time before continuing to edit their designs. And then at the start of the work day they are forced to repeat this operation every morning. This seems like a small problem, yet it is one that frustrates users and makes them dissatisfied with their software.
CAD developers do what they can to accelerate their software’s ability to load very large models more quickly. For instance, the popular Russian MCAD system KOMPAS-3D provides users with several different ways to do it:
- Load the model as a simple rectangular bounding box that represents the model’s extents
- Load a faceted version that represents the shape of the model
- Or else load the full model complete with its construction history
Each option loads progressively more data. While this allows users to select a faster or more detailed mode, the problem is solved only at the application level.
Another approach is to improve the speed at the file architecture level. JT, for example, is an open format, so it can be used by design systems as well as by 3D model viewers and more complex software that works with metadata. The developers of the JT format made it possible to load two representations of geometry simultaneously:
- Lightweight: the simple polygonal model
- Heavyweight: the detailed boundary representation
So, when users first load a 3D model, the lightweight faceted representation is loaded quickly, which can be used immediately for rendering (viewing the model). Then, if necessary, the heavier boundary representation is loaded, which is necessary for editing the model.
These two examples show that optimizing file-loading is in demand at the end-user application level and at the lower level one. It is for this reason that C3D Labs has been working at improving the performance of its C3D format, native to the C3D Modeler’s geometric kernel. We developed and implemented an extended format for storing the geometric model. This new format reads individual model objects from the file in random (programmer-ese for “arbitrary”) order, and gets information on the model’s structure and its objects without loading the entire model.
Let's look at the C3D format in greater detail, and see how the new one differs from the previous format.
How the Traditional C3D Format Worked
In the traditional C3D format, model objects are saved sequentially into one set of File Space clusters (see Figure 1) that has a single write point. If a geometric object refers to another object, then this inner object is written inside the object that references it. When a model object is referenced by several other objects, it is written inside the first object that references it, and is also included in the Registered Objects table. All subsequent objects that reference this object contain an index from the table.
Figure 1. Storing geometric model objects in traditional C3D format
The advantages to this approach are the minimum overhead when writing/reading the model, small file size, simplicity of the software implementation, and high usability of the API. But the approach imposes limitations on the use of the C3D format:
- Information on the structure of the model (or of individual objects) is obtained only after reading the entire model
- It is not possible to load objects in random order, or to import individual objects
These drawbacks occur because the C3D format does not provide information on the storage positions of specific objects. As well, when the object is nested in another object or refers to an object, its storage position is unknown.
And so, C3D Labs extended the C3D format to overcome these limitations.
About the Extended C3D format
To update the C3D format, the C3D Labs team first worked out in detail the requirements for the new structure. Some of these requirements had been already formulated, such as the independent storage of objects and the ability to read individual objects -- on top of accessing data from the file without needing to read the entire model.
Then they determined additional requirements: new interfaces for reading and writing models, reading individual model objects, and most importantly, maintaining compatibility with the current C3D format.
During the implementation stage, the developers determined where to save the properties and storage locations of objects, as well as the information about the hierarchy. They developed a table of contents mechanism, allowing for the independent storage of geometric model objects, implemented as follows:
- A specific object contains only those objects that are used exclusively by this object. As part of this approach, the objects belonging to each level of the model are saved in a separate file space, which can be switched between different write points while saving the file (see Figure 2)
- The object’s storage position in the file is used to reference the object
Figure 2. Storing geometric model objects in the extended C3D format
So, what is the final result? Now it is possible to perform single-pass processing of the geometric model while writing the model itself and its table of contents to file. The object tree, or table of contents, includes all objects belonging to the Items type. The object tree is saved to a file in the form of a flat list of nodes, where each node contains the following data for each object:
- Object type
- Object name
- Dimensions of the object and the local coordinate system (if applicable)
- Position in the file to write/read the object in the form of a cluster index and an offset in the cluster
- List of direct descendants of the node
- Object attributes
Application to CAD Systems
When loading a model from the new extended C3D file format, users can determine which objects should be read and displayed by name, type, size, and attributes (see Figure 3). This speeds up data loading when users want to read only part of the data from the file, instead of the entire model. The newly developed interface for reading data supports both the extended and traditional C3D formats, so compatibility with earlier versions is guaranteed.
Figure 3. Loading geometric objects from a C3D file by name, type, or size
http://c3dlabs.com/en/
[Tatiana Mitina is head of programming at C3D Labs. This article is reprinted with permission and first appeared at c3dlabs.com/en/news] |
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| Some of the most recent posts on my WorldCAD Access blog:
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Autodesk goes agnostic in its 'We have no god but Subscription and Subscription is its name' belief system. Get the details from Steve Johnson's report at www.cadnauseam.com/2018/02/12. For you of little faith, there is one act of penance you must suffer, Steve reveals.
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"Apple gave Samsung a huge gift last year when it set the price of its iPhone X at £999 ($999)" (The Register). When a big player increases its prices, it makes its competitors stronger, because they too make more profits now.
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Re: Autodesk Subscriptions
One of the companies I work for is very large, and likely has thousands of AutoCAD licenses. I'll try to send an email on Monday to their CAD manager as there may be considerable savings for them to have a similar number of BricsCAD licenses and a couple of AutoCAD rental agreements.
They can use BricsCAD for general work, and if a client requires a true AutoCAD file copy, the BricsCAD file can be loaded in AutoCAD, an operation like Zoom Extents executed, and the file saved as a 'true' AutoCAD file. A couple of workstations can be dedicated to producing true AutoCAD files.
Any good AutoCAD-compatible program can be used; I use BricsCAD as an example because I've used it for nearly a decade and found it very compatible with AutoCAD. I've loaded 50MB 3D files prepared with AutoCAD, modified them in BricsCAD, saved them, and opened them in AutoCAD without an issue.
- Dik Coates, P.Eng.
Canada
The editor replies: This is in fact a common tactic, and one that I think is a good idea. Some even replace the bulk of their AutoCADs with DraftSight as it is free, but not nearly as capable as BricsCAD.
The firm you speak of would benefit from reading chapter 5 "Operating Dual CAD Design Offices" in my BricsCAD for AutoCAD Users book, which they can download free from https://www.bricsys.com/en-intl/documentation/. It discusses from a practical standpoint how to work with two CAD systems, as well as two operating systems (Linux and Windows) in one office.
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What gear design and 3D modeling software is available for BricsCAD?
- Bob Price
Automation*Gears*Machinery
The editor replies: It appears that there are no gear modeling add-ons. The Bricsys applications list is online at https://www.bricsys.com/applications/.
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I was reading your ebook “BricsCADV17ForAutoCADusers-en_INTL.pdf”. It mentioned that there were no Color Books in BrisCAD V17. Would you know if the color books tab is in the Layer dialog box in V18? I would like to change our office AutoCAD to BricsCAD, but we do need to have the color books feature.
- Dixon
The editor replies: V18 does not. I've passed your request on to Bricsys.
Mr Dixon responds: It is too bad that BricsCAD V18 doesn't support Color Books. Our office really needs to use the third-party color palettes from Benjamin Moore for the building elevation design.
Looks like I can’t switch our office AutoCAD licences to BricsCAD yet. The current V18 is very good but with a couple of short comings like the color books.
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"Gadget bloggers tend to forget this is what the real world looks like: there are loads of people with three or four-year-old phones."
- Andrew Orlowski
www.theregister.co.uk/2018/02/12/samsung_analysis |
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