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Testing STEP format bootloaders for VR

We, BP Concept LLC, have been developing VR Concept software for organizing teamwork with any 3D model, including CAD, in virtual reality helmets for 5 years.

In this article, we would like to share the experience of integrating several downloaders to read various formats and dwell on how we implemented support for the STEP format using the C3D bootloader and comparison with the OpenCascade bootloader, which was integrated into our software earlier.



A little background


The purpose of our software is to help companies accelerate the coordination of projects between the decision maker, the project manager, contractors, partners and customers, by moving the discussion from the plane of drawings, pictures on the monitor and full-scale mock-ups into virtual reality, working with projects on a scale of 1: 1 (based on a 3D model) with the ability to consider it as if it had already been implemented or built. Using virtual reality technology allows you to increase the ergonomic characteristics of the projected object, reduce the number and cost of errors in the project, increase the efficiency of employee training in the workplace and reduce the risk of emergencies. In addition, the technology is used in the field of education.

To implement support for CAD formats, we use different approaches, ranging from independent implementation according to open standards, using Open Source, and also using commercial solutions, including CAD cores.

Implementing JT format support and getting to know the C3D Labs bootloader


Based on the results of working with current customers, we decided to implement the JT format, which is highly demanded in mechanical engineering, especially for customers who work with Siemens NX software. We analyzed different ways to implement such a bootloader, the main criteria for choosing such a solution were JT download quality, support speed, terms of use (annual payment, percentage of sales, features and conditions of replication) and price. As a result, we chose the solution of C3D Labs, especially since by this moment we were already beginning to work out integration with CAD system Compass-3D, of Ascon company. And C3D is the core of this CAD system.

C3D Labs also provides access to other formats, such as: JT, C3D, X_T, X_B, STEP, IGES and ACIS SAT. But some of these formats, specifically STEP and IGES, were already implemented in VR Concept with the help of another product - Open Cascade.

Partnership with C3D Lab was concluded in June 2019. In July, work began on the implementation of the JT format loader using C3D. It took us about 3 people-months and in the fall the loader was ready. The first users got a VR Concept build with JT support in September. And in October, other formats JT, C3D, X_T, X_B, STEP, IGES and ACIS SAT were implemented. We released the new version of VR Concept in December and it already had support for all these formats using the C3D core.

Testing STEP Loaders


The most popular of these formats is the STEP engineering format. And we had two load implementations using different libraries. The task was to make a choice or leave both implementations.

We decided to test the comparison of the two STEP loaders in VR Concept, implemented on different platforms.

For testing, we used 64 different models of the STEP format with different characteristics. The file size was varied (from 43 Kb to 269909 Kb) and the number of objects / bodies of the model (from 45 to 18483).


The model was provided by ASCON

. Depending on the above characteristics, the following table was formed according to the test results, showing the loading time of models with different number of bodies / objects:
The range of the number of objects (bodies)The number of models in the sampleVR Concept average load time with Open Cascade (sec)VR Concept average load time with C3D (sec)
1-10003932,59.84
1000-30002393,454,2
more than 3000245457.5

Three models were also selected for detailed indicative comparisons. Compressor (below), trolleybus (previous picture) and LEGO excavator. These models are quite voluminous, with the number of bodies more than 2000. One of them can be viewed and checked independently by reference . And this is how it looks with us:



Depending on the above characteristics, the following table was formed according to the test results:



Instead of conclusions


We did not expect to get such a result, to be honest! C3D turned out to be much quicker in reading the STEP format than Open Cascade, with the same settings and the visual quality of the result. In addition, it seems to us that the display quality of the C3D model is even slightly better.


Another comparison of the quality of visualization on an enlarged scale: above Open Cascade, below C3D. Compressor model provided by ASCON.

Yes, we did not compare both of these converters outside our solution, so if you have data on this subject, we will be happy to see them! Perhaps you have thoughts in defense of Open Cascade? Please share in the comments.

We continue to test and compare Open Cascade and C3D on different 3D models. We will be happy if you share your 3D models - we will test them and share the result!

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