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From CAD User Mechanical Magazine  Vol 15 No 02 - FEBRUARY 2002

We asked Robert Jamieson, an applications engineer with Autodesk who evaluates and advises on Autodesk software applications, including the hardware that it is being run on,

As has been written about in earlier editions of CAD User, Graphics cards are available in two categories in desktop or workstation PC's - those that use AGP (Advanced Graphics Port) or PCI (Peripheral Component Interconnect) as a means of utilising the computers graphic data. PCI was a standard method of providing expansion ports for peripheral cards, implemented sometime at the end of the Intel 486 processor period, and is still used today for undemanding add-in cards such as network interfaces.

As PCI was relatively slow at transferring data, it caused a bottle-neck in performance, and the AGP was established, instead, which could pass data at a much faster rate. The fastest currently is four times as fast as a standard PCI port. An AGP Pro, which has an extra long slot to provide more electrical power for high-end cards, is available on some machines, but in testing has found to be no faster.

One of the principal components of advanced graphics cards is the amount of RAM (Random Access Memory) it has - not to be confused with system RAM which is where all of your applications, data and Operating System are held and managed (Some cards can share this but they are always in lower performance category). Generally speaking, the greater the RAM available on a graphics card, the more colour depth can be obtained and more windows can be open at any one time. 32Mb is considered a basic minimum today and you should be looking at cards with at least 64Mb of RAM. Some of the problems that you get with too little RAM are black borders showing with multiple windows open or the screen display slowing down as the driver can't create the display list fast enough in RAM.

The Graphics Processor is also an important consideration and has the main effect on the card's performance. This, coupled with the efficiency of the software driver, gives you the speed of rotation - assuming the hardest task that the graphic card has to undertake is to rotate and re-display a complex 3D model.

OpenGL
Most CAD applications use OpenGL to display a model's geometry. This is a series of CAD oriented commands that know what a line is and how to display it without using the Central Processor Unit. This is stored in a display list stored in RAM on the card, freeing up the CPU for other tasks.

Many manufacturers of graphic cards say they support OpenGL, but this is not strictly true. A lot of cards only support a subset of the full OpenGL for use in 3D games such as Quake and Half Life. This means that if you set your CAD program to use OpenGL without a full OpenGL command set you will encounter problems.

Which raises a new question - "how do I set my CAD program to use OpenGL?". Finding the answer to that with Inventor is easy! To prove OpenGL is up and running, go to >Tools > Application Options, pick the hardware tab then click >Diagnostics. This shows all the supported OpenGL functions supported by the graphics card and therefore Inventor. The response shown is from Elsa's Gloria 2 card.

For Autodesk ® Mechanical Desktop, AutoCAD® 2002, Autodesk® Architectural Desktop3.3 you need to right click with the mouse on the command line and select Options, and then Click the System tab. In the top right part of the dialog boxes, where it says "Current 3D Graphics Display", click on Properties. This will bring up a new set of dialogue boxes. On the bottom left of these under "Acceleration", click the radio button to Hardware and select the file 'wopengl7.hdi'. This will load the OpenGL driver when you close the box. If you have Autodesk® Mechanical Desktop®5, you will want to select, instead, 'wopengl6.hdi'.

If you have a file open it might take a few seconds, as it needs to rebuild the display list. Now, before you stop reading to perform this operation, there are two further things that need to be done.
· Flash the BIOS on the graphics card to the latest version, if possible, by downloading it from your vendor.
· Download the latest graphics driver from your vendor and install it.

You can guarantee that the driver that came with the graphics card or the machine is quite old, as it has been sitting around on a shelf for a few months before you the supplier installed it in your brand new computer. Doing this will give your computer an immediate performance boost as most drivers get better with time. Nvidia quote a 30% improvement with its latest drivers over the original ones supplied with some of its cards.

This brings me to another important point. It is no good putting a very high end graphics card in an older machine, as it might improve the rotation speed, but as soon as you do another task the CPU will not keep up and slow down the performance of the card to the rest of the machine.

Name a good graphics card?
I am not saying all cheaper cards are no good for CAD. A lot depends on what drivers the manufacturers produce with these cards. As 3D games are popular and the functions needed for those are close to what you need for CAD, you can get the occasional bargain. 

Manufacturers that I have used that supply good drivers include Elsa (in financial trouble, use nVidia drivers), Fire GL who used to be Diamond MM and are now ATI, and the Integraph Wildcat series (was 3D labs, now Creative Labs). As you can see there is a lot of consolidation in the market.

My current PC's have FireGL 2 and an Elsa Gloria 3. These both give good results with the FireGL being about 20% faster. How do I know this? Well, inside Inventor there are two hidden graphics speed tests. You can see some results from these by looking at http://www.autodesk.com/support , posted under Inventor 5.3 Graphics benchmarks. The page also gives some results on cards that have been tested that conform to OpenGL. The results are applicable to other CAD software that uses OpenGL.

Inventor makes use of textures in the modelling environment, putting further demands on graphics cards. So that we could investigate relative performances under these tasks - a different ballgame to rotation - MaxBlack lent me a new Dual AMD workstation with an nVidia Quadro4 750 and an ATI Fire GL8800 installed. The first thing we noticed was that the increased CPU power helped the graphics performance with the Kart model shown below. Inventor performs some trickery to enable the graphics to maintain good rotational performance.

The ATI card kept the textures on the Kart, as it rotated, with no problems at first, but the geometry degrading on the speed of rotation was increased. With the Quadro4 the textures and geometry performed together consistently throughout. MaxBlack said that an impending improved driver for the Quadro4 would even double the current texture performance, and my quick testing confirmed what MaxBlack results had shown. The good news for those building a CAD system is that the Quadro4 starts out at just at £300!

The Fire GL 2 was faster than the ATI GL8800 in my quick tests, which makes it look as if ATI have some work to do to make its new card a success - although its first attempt is not without merit. The ATI range of cards, however, raise problems with many CAD programs and can't, therefore, be recommended for the CAD environment, as it is more of a games card.

Conclusion
So, if you have a graphics card that doesn't work quite as fast as you would like, the first thing to do is to update the driver. Consider your Operating System as well, as OpenGL works better under Windows NT, 2000 and XP. Windows 98 and Millennium do not support it as well and, furthermore, tend to be less stable platforms for any software. 

The next stage is to use some benchmarking software to test the performance of the cards. SiSoft's Sandra can give you a rough-cut idea on the performance of graphics cards, and it can also be used to evaluate your computer's general performance. The software can be used to highlight any of the problems with your set-up that can be slowing your application down. CU
www.nvida.com
www.ati.com

Case Study

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