Performance

The Residential HVAC Load Calculation Extension software system is a residential and light commercial HVAC load calculation software package based upon the ASHRAE 2001 Fundamentals algorithms (Chapter 28). This program is geared specifically toward the design/build mechanical contractor, design mechanical engineer, and architects.

The purpose of this software is to provide the user with total cooling and heating loads for a building so that they may properly specify the correct size HVAC equipment (whether it is a packaged rooftop unit or a boiler).

Jason Grant has a blog of his Benchmark results comparing 32-bit vs. 64-bit Revit software.

"Before the 64-Bit was even released I was just finishing up a benchmark
program that was very difficult and taxing on RAM and processor. We were trying
to figure out what laptop would be best for our Revit users. Since the 64-Bit
has been released I have now run it and was shocked at the improvement. On
another note, I was let down that the SP2 for 2009 was actually slower then the
WU1 but that quickly disappeared when I heard about the 64-Bit version. "

Click here to see his results:

White Paper From Autodesk View PerformanceThe largest impact on View manipulation performance (scroll, pan, zoom operations) is the Model Graphics Style settings. The Hidden Line Style, due to the requirement to dynamically generate gaps and hidden lines when elements overlap in the View, requires the most processing and thus results in a noticeable performance impact in Views with many visible Elements. The following best practices will help to mitigate this performance impact and streamline project workflows. Modeling and Sheet ViewsIn order to streamline project workflow, it is recommended to create both Modeling and Sheet Views for the same regions of the building.Follow these guidelines

• Modeling Views should be configured to utilize the Wireframe Model Graphics Style.
• Sheet Views should be configured to utilize the Hidden Line Model Graphics Style to produce the desired appearance for Construction Documentation.
• Use Dependent Views for your Sheet Views. This allows you to have multiple regions of an overall Level in different views, while not requiring duplicate Annotations.
• Differentiate Modeling Views from Sheet both in View Name and Sub-Discipline, as see to the right in Figure 1. This will provide a logical organization of the view for users, and help to ensure proper usage.
• Utilize View Templates to streamline the creation of these Views and achieve consistency.
• Utilize Duct and Pipe Color Fills only in your Modeling Views, where the Wireframe Model Graphics Style is used.

Figure 1 - Modeling and Sheet Views Optimizing Hidden Line PerformancePerformance in Views with the Hidden Line Model Graphics Style enabled is directly related to the number of Faces displayed in the View. While Elements appear as 2D Lines in a Revit View, they are 3D Objects made up of faces in the model. It is those faces that are processed Revit by the Revit graphics system and show up in the View as 2D Lines. Use the following best practices to optimize the performance of your Views with the Hidden Line Model Graphics Style enabled.

• Avoid using Fine detail level when working in mechanical views if not necessary, as this displays Pipes as 1-Line Medium detail level is useful for Views working with HVAC systems.
• If using complex 3D Components in your Building Service designs, turn off the visibility of the complex 3D geometry in your Sheet Views. In place of the complex 3D geometry, utilize Model Lines that convey the overall component shape in the Family definition. Make those Model Lines visible in the Detail Level defined in your Sheet Views.
• If not necessary for documentation of working on a View, set the Inside and Outside Gap settings for Hidden Lines to 0, as seen on the right in Figure 2. This can provide substantial performance improvements.

Figure 2 - Turning Off Hidden Line GapsModel Manipulation PerformanceRevit MEP allows users to create models of Building Services, often in the form of large connected networks. The powerful analytical capabilities of Revit MEP, in conjunction with the Revit Parametric Change Engine, allow data to flow throughout the connected network when manipulations are made. Improper structure and configuration of large connected networks has been shown to have a severe impact on model manipulation performance. In comparative testing, models have been shown to perform up to perform significantly better when structured properly. As a connected network grows, the performance of model manipulations (moving Elements, changing Flows, connecting new Elements, etc.) is impacted by a number of factors. Understanding these factors, and adhering to the Best Practices outlined below, will allow for optimal model performance. Create Systems Create logical Systems for your connected networks, rather than leaving all Elements on the "Default System". Associating Elements into Systems helps to streamline data propagation and facilitates the analytical uses of Systems like Pressure Drop calculations. Testing of customer models with all elements on the Default System showed significant improvements when the connected network was re-structured as logical Systems. Set Correct Connector Flow Directions Ensure that the Flow Direction Parameter for Connectors on Families in the connected network is not set to Bidirectional unless the Family is placed in-line with connected networks like Dampers and Valves. This can make flow determination more difficult and thus impact regeneration performance. Create Strategic Breaks and/or Use Multiple Files While maintaining the entire design for a building service in one well connected model allows for full data propagation, the size of the connected network is directly related to its manipulation performance. Testing has shown a linear decrease in manipulation performance as a connected network size grows. The rate of decrease is directly related to the topics mentioned in this section. As the performance of connected networks decreases with larger size, the benefits of data propagation and connectivity are overcome by the need for better model manipulation performance. Thus, for large projects it is a best practice to employ one or both of the following strategies to ensure productive manipulations of your connected networks.

• Strategic Breaks - Creating disconnections in a connected network stops data propagation during model manipulations, as well as the constraints engine that maintains connections. Product Team testing has determined that strategic breaks in a connected network produces the most significant improvements in model manipulation performance. The recommended practice for this strategy is to create disconnections at logical sections of the connected network. For example, in a VAV air distribution system, create disconnections at the upstream connection point on the VAV box. This allows the VAV flow to still be calculated based upon the downstream Air Terminals. A Duct System Schedule can then be used to manually coordinate flow at the Air Handler or Package Unit. The most efficient way to accomplish such a disconnect, while still maintaining proper appearance for documentation, is to model the upstream element without connecting to the VAV and then using the Align tool to locate the end of the Duct at the same location as the VAV connection. To download a video showing this procedure, click here.
• Multiple Files - For large, complex buildings, using strategic breaks as well as the aforementioned best practices may still not provide optimum model manipulation performance. In these cases, the model should be built across multiple Revit Project files. There are two fundamental ways to structure the MEP project files, by MEP discipline and by region of the building. Both of these approaches have their benefits and drawbacks, and ultimately it is the choice of the BIM/CAD Manager.
• By Discipline This strategy creates separate Project files for each MEP discipline, such as a Mechanical, Electrical, Plumbing, Fire Protection files.
• By Region This strategy creates separate Project files for different regions of the building, keeping all disciplines in each file.

In order to achieve optimal coordination between the MEP disciplines, each discipline must be within the same Revit Project file. This allows disciplines to connect to each other’s elements directly, like electrical connections or drain connections on mechanical equipment. Additionally, Product Team testing has shown that separate connected networks do not have a significant impact on each other; a duct network does not have a significant impact on model manipulation of a plumbing network in the same Project file. With these considerations in mind, it may be helpful to structure large projects by region of the building. Simplify the Display of Architectural ElementsSimplifying the display of architectural elements may help improve performance by reducing the visible elements that must be generated and maintained within the view. This may be done by overriding the Detail Level in the view. For example, the Coarse Detail Level may be applied to walls even when the view is configured to use Medium or Fine (refer to figures below). In the Visibility / Graphics Overrides for the view, set the detail level of the appropriate components to the simplest level acceptable. These settings may be configured in view templates and applied to your views to quickly simplify the detail level throughout your project. Figure 3: Wall with medium detail level in medium detail view. Figure 4: Coarse detail overrides for architectural elements. Figure 5: Wall with coarse detail level in medium detail view.

I recieved comment from Alan Saldich, the VP of Product marketing for Riverbed and below is his message. He told me basically that this is not a Riverbed issue, but an Autodesk issue, and that all WDS solutions are affected by the file format change. Here is his letter.I’m the VP of product marketing for Riverbed, and I wrote a lengthy post yesterday on this topic, which can be viewed here:http://www.wdsforum.org/forum/index.php?showtopic=183Silver Peak has admitted (in a call earlier this week with the TechTarget reporter who wrote that article) that the issue with the AutoCAD 2007 / 2008 .dwg file format is *not* specific to Riverbed and *does* affect all products that use deduplication in their solutions, including their own. The only way to determine the degree to which any particular WDS solution is affected by the file format is to do your own testing. Remember, the problem is most pronounced with the ISAVEPERCENT (Incremental Save Percentage) set to zero, which forces a complete save, and which causes all the bytes to be scrambled. Using a non-zero value for that setting (like the default value of 50) reduces , but does not entirely eliminate, the impact of the new file format on WDS solutions.Unfortunately this is not an issue that can be solved by Riverbed or any other WDS solution provider - it was caused (inadvertently) by the way Autodesk decided to change their file format, including scrambling the bytes on every complete save. Any product that tries to find duplicate data will be affected, possibly to a varying degree, but there is no doubt there is an adverse effect.Alan SaldichVP Product Marketing & AlliancesRiverbed

• I'd like to post my own response to this as Riverbed's VP of Product Marketing and Alliances. I know this is a frustrating issue for our customers who rely on us and on Autodesk, and that's why we did the webcast in the first place a few weeks ago - to explain the issue as best we could. I have personally been working on this issue extensively for the last few months, and especially in the last few weeks. Let me make a few points and give you all an update.We have worked with Autodesk directly on this and we know what causes the problem, and Autodesk agrees with us. It is definitely not specific to Riverbed. Let me be clear: There is absolutely no dispute about that. Autodesk has had developers looking into the issue with their new file format to see if there's something that can be done. Unfortunately as of this moment there is no immediate fix. The problem is caused by a rescrambling of the bytes in Autocad 2007 / 2008 files upon a complete save, and that causes "cold" performance on writes. Reading files across the WANReads are generally fast because if the file in question has been written across the WAN before, then the bytes have not been re-scrambled and the read is fast, as usual. However, if you have a highly collaborative environment where someone in the other office could open and re-save the file, in that case the second read across the WAN could also be slow (because the bytes are again re-scrambled).If users are using other versions of AutoCAD or Civil 3D that don't rely on the newer file format, then they are not affected. The rescrambling is not compression nor encryption - it is an inadvertent byproduct of performance improvements that Autodesk made in an effort to make AutoCAD work better (nothing to do with WANs at all).The only option right now is to leave the Incremental Save Percentage (ISP) setting at its default setting of 50 - that works much better than forcing a complete save. There's some confusion here about whether a setting of 0 or 100 is the one that causes the complete save, and we're trying to clear that up (anyone know for sure?).Several of our competitors (Cisco and Silver Peak primarily) are trying to take advantage of this issue by claiming that it is somehow specific to Riverbed, and that is where a lot of the confusion and angst comes from. Silver Peak has probably been the most aggressive on this front. Unfortunately, they have been wrong about (1) how Riverbed is impacted by this and (2) claiming that they are not affected by the problem. Silver Peak has conceded (yesterday) that (1) this is not a Riverbed-specific problem, but rather it's caused by the way .dwg files are written in the new format, and (2) their products are also affected by it.If you read their claims carefully, and after talking with them it became more clear, their claims that they work well with AutoCAD 2007 / 2008 are couched in terms of average deduplication rates across a range of ISP settings (remember the only relevant use case here is a complete save, not incremental saves), across other Autodesk products like Revit (again, not relevant because Revit does not use .dwg files and is not affected by this issue), and by including other irrelevant operations like FTPing the same file over and over (again, not relevant because the files are not re-saved and therefore the bytes don't get scrambled again, so you get "warm" performance). Just to reiterate again... the problem occurs only when you do a complete save.Silver Peak still claim to be less affected - we'll see if that's true and by how much). The only way to document that will be through publicly available testing of both products under the exact same scenario. We are working on that through a customer who has their products and we will publish the results as soon as we can. We have already completed testing with Cisco's products and Blue Coat's and we have demonstrated the same problem affects their products in almost exactly the same way. As for our products being 'bricks', I'm very sorry you feel that way. If you are having problems, I would like to help you set up a support call to make sure there isn't some other issue like a duplex mismatch or other networking-related issue.We have literally hundreds of architecture, engineering and construction companies all over the world who rely on our products to accelerate AutoCAD, including most of the large multi-site firms in the US. Overall, as of December 31st, we had over 3,500 customers in virtually every industry and over 40,000 Steelhead appliances in use, so it's hard to believe that this is a systemic problem. If you or anyone else on this board would like to talk to me personally, I'd be happy to. My email is alan@riverbed.com, and my cell phone is +1 650 888 4032.

Article sent to me from a user. Thanks for the link. I summed up the article below. From the article, it sounds like Autodesk doesn't have a solution yet. I don't know much about the various WAN acceleration applications, but I thought I'd share these articles with you.It seemed like a good idea at the time...By Bryan Betts, TechworldA changed file format has sparked off a fierce war of words between users, WAN acceleration vendors and Autodesk, which significantly changed its DWG drawing file format in both the last two versions of AutoCAD. The result, is that WAN optimisation gear from the likes of Riverbed Networks - which has a strong user-base in CAD - is no longer able to accelerate file transfers over the WAN. Given that many CAD-using companies need to share drawings across multiple offices, that's a big problem. At issue is a new dynamic file format which deliberately makes a saved file look completely new, even if it is only an edited version of an existing file, says Riverbed VP Alan Saldich. That means block-level caching schemes can't do what they'd normally do, which is to send only the changes over the WAN. Format errors "To improve the speed of the application itself, they changed the file format so that every time you change the file, every bit gets scrambled," Saldich explains. "If you FTP the file twice or reopen it without saving, we can work on that."There's only two ways to solve it. One is for Autodesk to revert to the former file format, which seems unlikely. The other thing is they could tell us enough about the file format to undo it." Saldich explains.In the meantime, Saldich and Autodesk VP Guri Stark have issued a joint statement advising affected users to do one of two things: either revert to an earlier AutoCAD DWG file format; or adjust an AutoCAD setting called Incremental Save Percentage (ISP) to 50, which reduces the amount of data scrambling when a file is saved. Other WAN acceleration companies have used the issue to bash companies such as Riverbed for developing application-specific optimisation modules. However, Saldich claims it's nothing to do with those - he says they're just protocol optimisations to reduce the number of round trips, and they don't deal with file formats. He argues that it's one of the first symptoms of a bigger problem that is only just emerging now."It affects any product that relies on data de-duplication, including backup and replication," he says. "I truly think the AutoCAD team were unaware of this when they did the development work back in 2004, as data de-duplication wasn't common then. "The bigger story here is that de-duplication is a widely-used technology now, and software developers need to take account of that. We are 100 percent certain of the problem, and any vendor has the same issue, which is that you don't get to look at the data before it gets written to disk." Aaron claims Autodesk had its own reasons for formally testing his company's gear - it is a Silver Peak user, with some three dozen of its WAN optimisers around its organisation. Aaron acknowledges though that when Saldich argues that application developers need to be better aware of how their software will run over a WAN, he has a good point. "The more the software developers do to address this, the more we all benefit," he says.We asked Autodesk for its comments, but nearly two weeks later the company had still not found a spokesperson or offered any feedback.

Some activities in Project Navigator, such as loading xrefs, take what seems like a long time. This is normal. These processes need to run their course before other activities can be initiated. I was recently working with a client who is creating a large hospitol project using AutoCAD Architecture and AutoCAD MEP and project navigator. I noticed how long it was taking to open constructs, views and sheets and so I looked for some info that could help them be more productive and came across some tips to help improve performance of their project navigator.The specific activity of dragging a view to a sheet actually involves several background processes, including loading all the files in nested external references, updating project database files, managing layers for viewports, scaling geometry, and coordinating data fields and labels.For your network environment, follow the guidelines below:

1. To rule out any potential problems with your network environment, temporarily copy the project files to a local workstation and perform the same operations with Project Navigator. Compare the speed in both environments to determine if the problem is directly related to network speed.
2. Use a Windows operating system on your server. AutoCAD MEP only supports a Windows networking environment. If you are using a Novell or UNIX server, you will need to install the Windows Client for these operating systems. However, due to the permission restrictions on these operating systems, the performance of Project Navigator can be dramatically affected.
3. Install the most recent service packs and patches for the version of Windows installed on your server.
4. Check for the presence of antivirus and spyware applications on your system. These applications have features, such as Symantec's Auto-Protect functionality, that constantly monitor the files on your computer or server. This type of application can slow performance down because files are being scanned while they are being used. If you are using this type of virus protection, try disabling it to see if performance is affected. You should disable this feature on the server as well. If you want to leave this feature enabled, you can set up exclusions for the files and folders you use with your projects.

For your workstation, follow these guidelines:

1. Install the most recent service packs and patches for the version of Windows installed on your workstation.
2. Disable Digital Signatures in AutoCAD MEP: In the Registry Editor, look for the following key: [HKEY_CLASSES_ROOT\CLSID\{36A21736-36C2-4C11-8ACB-D4136F2B57BD}\InProcServer32] Delete the content of the Value Data field for the Default item.
3. If you have custom hatch patterns, make sure that they are not loaded as part of the or files. Any custom pattern should be saved as a separate PAT file in the support directory location.

For your project files, follow these guidelines:

1. When working with Project Navigator, all users should be using the same version of AutoCAD MEP. Every new version of AutoCAD MEP introduces additional information saved on the project files and that can create conflicts and slowdowns if different versions are used to read the same files.
2. If you are using old template files, cut the entire contents and paste them into an updated AutoCAD MEP template.
3. Purge unused block definitions take up a lot of file space in all drawings.
4. In all drawings, including the template drawings used by Project Navigator, the value for the variables should be set to the predefined value: INDEXCTL = 2 (Spatial indexes are created) XLOADCTL = 2 (Enabled with Copy. This enables demand loading, but uses a copy of the referenced drawing, so others can edit the original drawing.)
5. Manage the temporary files that are created as part of the “Enabled with Copy” demand load strategy built into Project Navigator. These files remain after a system failure or an aborted Project Navigator activity. Deleting the AC$ files in the Temp folder can reduce the time required to open most drawing files and significantly improve system performance.
6. Minimize Multiple Sessions. Launching multiple or concurrent sessions of AutoCAD MEP, AutoCAD Architecture, AutoCAD, or Revit MEP dramatically reduces system performance and may possibly affect the overall stability of the system. Avoid this practice and adopt other work methods. If you cannot avoid multiple sessions, consider using your most capable workstations in these situations.
7. Before dragging views into sheets, temporarily unload external references from the view drawings. Drawings with attached xrefs will reproduce that xref. This can lead to duplicate or circular xrefs and confusion as to what should actually be in the drawing. This can tax workstation resources and affect performance.
8. Check for the presence of the following blocks in all your drawings, and delete them: AVE_GLOBAL, AVE_RENDER, RM_SBD
9. Detach any AutoCAD CAD Standards associated with the individual drawings. This can be done on the CAD Manager menu, under AutoCAD CAD Standards.
10. Change the FIELDEVAL variable to [2], so field values are only updated when the drawing is saved.

In March 2006, Autodesk changed the DWG file format for AutoCAD 2007 to make it more compact and improve performance for AutoCAD users. Autodesk’s customers widely welcomed this change and almost all AutoCAD users have enjoyed improved performance.However, Autodesk and Riverbed have recently received reports that some customers using some WAN acceleration appliances, including Riverbed’s Steelhead appliances, have experienced noticeable reductions in write performance when working with files saved in the AutoCAD 2007 “DWG” format. One of the side effects of the DWG format changes is that when users perform a complete save from within AutoCAD (as opposed to an “incremental” save), virtually every byte of the file gets changed – even if zero changes were made to the file itself. The net effect is that writes that would normally affect only “warm” data are actually “cold”, due to the reordering of the data in the file.Users of Riverbed or other affected WAN acceleration solutions can implement the following immediate workarounds that improve write productivity.

1. Using a feature in AutoCAD called “Incremental Save Percentage” (ISP), and setting it to 50
2. Using a version of the DWG format other than the AutoCAD 2007 DWG format.

The performance and productivity of their customers is a key consideration for Autodesk and Riverbed. Both engineering teams are working together to devise workarounds and are examining potential longer-term solutions. Given Riverbed’s experience in WAN acceleration technology, our joint work may also provide solutions for customers of other WAN acceleration or deduplication technologies, who might be experiencing similar issues with write performance.

There is an issue with AutoCAD MEP where you cannot draw more than one segment of pipe or duct at a time. When you are prompted for starting point, and ending point of the first segment, the command exits without allowing for additional segments. The Civil 3D Object Enabler breaks the pipe/duct add mechanism. The Autodesk development team has tentatively scheduled to deliver a fix in the next update to the Civil 3D Object Enabler, available in approximately two to four months. Please note their quality assurance teams may need to reschedule some fixes. Please rely on the timeline information as a guideline only and not a guarantee.If this is happening to you, you only have two options as of now. Uninstall the Civil 3D Object Enabler, or continue with the add duct/pipe tool ending after each segment is added.

Hidden Line CacheThe Hidden Line Cache is a feature that was implemented in order to improve the loading performance of drawings that contain ABS Objects, with the Hidden Line feature turned ON. It’s usage, which is a drawing-specific setting, is controlled in the ABS Crossed Objects tab of the Options dialog.Fig 5 – Hidden Line Cache ControlAs described in the Hidden Line Routine section, the end result of the Hidden Line routine is the assignment of portions of ABS objects to a Hidden Display Component. This assignment is not actually stored on the object themselves, but rather in a separate section of data.The Hidden Line Cache feature allows for this data to be saved into the drawing database itself. This means that the data will not need to be rebuilt the next time that drawing is opened, since it already exists in the drawing. Without this option checked, the Hidden Line data will re-built each time the drawing is loaded, and exist only in the system RAM until the drawing is closed. The storage of the data in the Hidden Lines Cache will increase the overall size of the drawing file, sometimes significantly depending on the Hidden Line data generated by the routine. The tradeoff is that the drawing will load significantly faster with the Cache in place at time of load.Hidden Lines and XrefsThe existence of loaded xrefs that contain ABS objects, which are set to display Hidden Lines, in a host drawing will have a significant impact on the behavior of Hidden Line data for the host drawing. Since the xrefs contain ABS objects that will be factored into the Hidden Line routine, the program cannot know if those objects have changed significantly since the last time the host drawing was opened. Such a change would result in any data saved in the host drawing’s Hidden Line Cache not to be in sync.Because of this potential for incorrect Hidden Line data of xrefed ABS objects, the data is never saved in the host drawing’s Hidden Line Cache, regardless of the setting highlighted in figure 5. This means that the Hidden Line data will be to be re-built EVERY time that the host drawing is loaded. This process can take a significant amount of time to complete, depending on the complexity of the layout.This is why there may be a significant difference in load time between simply opening the xref directly and opening a host drawing that contains that xref.Hidden Lines and Viewports on LayoutsIn a given layout, each viewport has its own active Display Configuration setting. You change this by double-clicking in the viewport and making it active, and then changing the active Display Configuration. This allows for different viewports to display the same objects in a different way. An example of this would be a 1-Line and 2-Line display, as seen below.Fig 6 – Different Display in ViewportsIn some circumstances, a new Viewport is created with an active Display Configuration that uses Hidden Lines. Be aware of this setting, and make sure to use a Display Configuration that does not utilize Hidden Lines if the feature is not needed.Mitigating Performance Impact of Hidden LinesWith a better understanding of the Hidden Line feature and how to control it, one can better make decisions regarding its impact on performance. The following items may be helpful in mitigating the performance impact of the Hidden Line feature.

• First and foremost, have a Display Configuration that does not use the feature, and use this when display of Hidden Lines are not needed. Using such a “non-hidden line” Display Configuration will result in a significant improvement in load performance of a drawing, especially when there are xrefs containing ABS objects that use Hidden Line feature to display. Additionally, the existence of the Hidden Line data in the system RAM can have a significant impact on overall program performance. When new ABS objects are placed in the drawing, or existing ABS objects are moved, the Hidden Line data may need to be updated. This can add additional time to commands, potentially reducing productivity.
• On a Paper Space layout, be sure to set the active Display Configuration for a viewport to a “hidden lines” Display Configuration only if such display is needed. If there is only text or non-ABS objects in the viewport, make sure to set active a “non-hidden lines” Display Configuration. This can make a significant impact on the time it takes to display the Layout.
• If only using Hidden Lines for coordination, consider turning off Hidden Line gaps. This additional calculation in the Hidden Line routine contributes to the overall calculation time, and adds additional size to the Hidden Line data stored in system RAM.
• Because of the impact of xrefs in a host drawing, as discussed in the Hidden Line and Xrefs section of this document, consider how you plan to structure your project drawings, and what xref relationships will be created as a result.
• Unless there are specific reasons to reduce the physical size of drawings, consider using the Hidden Line Cache feature when possible. This will help to improve drawing load performance in situations when the Cache is utilized.
• Flex Duct objects contain annotation lines that give them the “flex” appearance. The style of these annotation lines can be controlled by the user. Some of these styles use extensive linework to give the desired look for Flex Ducts. These annotation lines are included in the Hidden Line Routine, and can add significant complexity to the calculation. Unless you require that Flex Ducts be shown with Hidden Lines, consider using the 2 Line Display Representation to display these objects in your drawings. This can reduce the complexity of the Hidden Lines Routine, thus improving load time and reducing the overall size of the Hidden Line data stored in the system RAM.