The Building Coder

Slab Boundary

Developers have frequently asked how to determine the boundary polygons of a horizontal slab, e.g. the loops formed by the bottom edges of all the vertical or 'side' faces in this floor: In this case, there is one outer and three inner loops, one of which is circular. There are several different possible approaches to obtain this information, and you will need to decide which is simplest or most effective or optimally suited to provide the data you require in... Read more →

Element Bounding Box

Here is a topic suggested by Michael Raps of the Institut 4D-Technologies and DataSpaces at the Fachhochschule Nordwestschweiz regarding the Element BoundingBox property. This property is documented in the Revit API help file, which says that it retrieves a box that circumscribes all geometry of the element. It takes a parameter of type View, from the Revit Elements namespace. According to the help file, it returns a bounding box for the model geometry if the view parameter is null, and... Read more →

Obfuscation

In response to the last post, Rod Howarth brought up the related topic of source code obfuscation for a .NET assembly. He says: Reflector is certainly a useful tool, and it’s good to delve into both your own code and other namespaces. It can greatly assist with understanding code and also disaster recovery, in the case of lost source files. A related topic is obfuscation, as the first thing that one thinks about when you realize that your DLL file... Read more →

Converting between VB and C#, and .NET Decompilation

Here is post to follow up on the comment on converting between C# and VB code by Rod Howarth on the post on Application Events in VB. First of all, converting code between C# and VB is possible and can be done automatically. C# and VB.NET both produce the identical intermediate language IL code, which is what is actually stored in the .NET assembly and evaluated by the .NET framework. The IL code contains all information required to regenerate the... Read more →

Azimuth

Several developers have asked how to determine the azimuth of an element, i.e. the angle between the element and true north. This calculation is obviously strongly affected by the project location. Determining the angle of an element is pretty simple. All Revit elements have a Location property. For some, the location is a point, while others can be line or curve based, in which case their location is an instance of the LocationCurve class. One of the properties of the... Read more →

Family Instance Materials

In the previous post, we read out materials from walls and other building elements by querying them for their geometry, picking out all the solids, and iterating over their faces. However, for family instances such as doors and windows, we noticed that no solid is present in the top level objects contained by the geometry element. Family instances make use of a geometry instance to define their geometry. The geometry instance provides the facility to reuse symbol geometry in multiple... Read more →

Element Materials

I recently heard several queries on how to access the surface material of a wall or other building element. There are several different ways to access materials defined on building elements. One method is discussed in the section 16.3 Element Material in the Revit 2009 API Developer Guide. Another method goes through the geometry and retrieves the material associated with each face. We will discuss the latter approach in this and the next post. Retrieving the material associated with element... Read more →

Application Events in VB

I do not work much in VB, but somebody recently asked how to subscribe to the Revit application events in that language. There is no VB sample for this in the Revit SDK samples, so I created the following little solution to demonstrate it. The steps to create it are exactly the same as for a C# project, and were actually described in detail for both C# and VB in the post on Debugging a Revit Add-In, but here is... Read more →

RVT File Version

And now for something completely different. The Revit API does not provide any method for determining the version of an RVT file on disk. And even if it did, it would often be useful to be able to determine the file version from outside of Revit, i.e. without having access to the Revit API. Happily, this is easily possible and also gives us a chance to look at a completely different programming environment, for a welcome change. To see how... Read more →

Picking a Point

I am regularly asked by developers how to pick a point in Revit. This is currently not possible. The wish has been registered, but there are no plans to provide this functionality in the short term. The only interactive selection methods available in the API are the PickOne() and WindowSelect() methods on the Selection class in the Autodesk.Revit namespace, which prompt the user to select one or several building elements. If you need the user to specify a point somewhere... Read more →

SDK Update Posted

The Revit 2009 web update 2 has been posted to the Autodesk product site for the English versions of Revit Architecture, MEP and Structure. Unlike previous versions, this update makes use of patching technology and does not require a complete reinstallation. For this reason, the SDK is not included in the update, like it used to be in previous versions. Therefore, the Revit 2009 SDK web update 2 has been posted separately. It is available under the link Revit 2009... Read more →

Filter Performance Conclusion

Continuing the topic of the Revit API filter performance, Guy responds to Ralf: Ralf raises some good points. A good point on the order in filters, I did not think about that and I did think the speed improvement was larger than normal. I've found in past testing using the TypeFilter in most cases 2-10% slower than using some form of .NET filtering for real world projects and where other filters are not appropriate. I agree that an anonymous method... Read more →

More Filter Performance

This post is a response to Guy Robinson's contribution on Filter Performance, and is also by a reader, Ralf Huvendiek. Ralf only recently started working on the Revit API, but brings such a wealth of prior programming experience and enthusiasm that I am very grateful for his invaluable input. He says: Guy raises an interesting question regarding the performance of the Revit filters. I think he comes to the right conclusion, but not the best solution or explanation. First we... Read more →

AU 2008

I am very much looking forward Autodesk University 2008 in December in Las Vegas, where I will be presenting classes on some Revit API topics: DE101-3 The Revit SDK Sample Smörgåsbord Tue. 12/2 8:15 am - 9:45 am DE205-3 Enhancing Your Revit Add-In Wed. 12/3 10:15 am - 11:45 am DE301-2 The Ins and Outs of Revit MEP Programming Thu. 12/4 8:15 am - 9:45 am I will also be part of the panel for DE315-1 AEC API Talk Thu.... Read more →

Filter Performance

This post is entirely thanks to Guy Robinson, who has always been the quickest to test and comment on performance issues in the Revit API, in response to the previous post. He says: Like you, I initially thought the TypeFilter was a more elegant filter for FamilyInstances etc., but having done a lot of testing I now have my suspicions regarding how filters work internally and why it's not necessarily a good filter option for certain element types. In the... Read more →

Relationship Inverter

Moving away from the topic of geometry, I have another sample that I would like to share from the Revit API introductory workshop that I recently held. In this sample, we address the following topics: Using a Boolean combination of Revit API filters to find certain elements. Retrieving the hosted to host relationship between doors, windows, and walls. Inverting the relationship, i.e. determining the host to hosted one. This sample also introduces some new little utility functions, such as ElementDescription()... Read more →