The Building Coder

Analytical Support Tolerance

Here is an interesting issue dealing with the analytical model in Revit Structure. As we see below, the issue is not really API related, but since one symptom is the missing data obtainable through the API, it is worth an explanation.

Question: We have created two columns over a three-pile cap foundation and are trying to retrieve the support data from their analytical models:

Unfortunately, the support data of the column is available only if its centre line is exactly over the analytical model location of the pile cap foundation. Else, it is not available and the property simply returns null. The main purpose of this requirement is actually to find the link between the column and the pile cap. How can we achieve this, please?

Answer: Happily, this situation is easily resolved by modifying the analytical support tolerance. First, note that the missing support data is not an API-specific problem. If you select the column through the user interface, the Show Related Warnings button is active and the warning says that the column may not be supported.

The pile cap foundation is actually four foundations – one cap foundation and three pile foundations. Geometry for the cap foundation starts at Level 1 and goes down 900. The geometries for the three pile foundations start at -900 and go down 6900. In Revit, the default position for the Isolated Foundation analytical model is at the top of the geometry. Since this is at -900, the analytical models for the pile foundations are at that elevation.

Analytical Support is governed by the Analytical Support tolerance, shown on the Analytical Model Settings tab of the Structural Settings dialog. In the attached file, this tolerance is set at 300. So even when the column's analytical model is directly over the pile foundation's analytical model, the thickness of the cap foundation (900) is keeping the column from seeing the pile foundation's analytical model.

To overcome this obstacle, increase the tolerance from 300 to 900. Then when you move the column over the top of the pile foundation, it will see the pile foundation, and the column will consider the pile foundation as a valid support.

Although that resolves the current problem, here are two additional general hints for approaches to find the link between two elements located close to each other:

• FindReferencesByDirection.
• Geometric analysis.

The FindReferencesByDirection method to find the link between the two elements determines that the pile cap foundation is located directly underneath the second column and hence is supporting it. This can be achieved by shooting a ray straight down from a point slightly raised up from the lower endpoint of the column and using FindReferencesByDirection to discover the foundation element directly underneath. FindReferencesByDirection returns an array of elements, faces, and references found when moving through the model from a specified point in a specified direction. Its use is demonstrated by the RayTraceBounce SDK sample.

You can also determine their relationship by pure geometric analysis, e.g. using a filter to collect all the structural elements on the relevant levels and then comparing the locations of their solids' faces with each other. The AreSolidsCut method defined by the RoomsRoofs SDK sample may be helpful in this context. Geometric analysis may or may not be simpler than using FindReferencesByDirection.

Unrotate North

I spent this weekend on the Rigi Mountain together with seventy other people from the alpine club. Saturday it rained quite hard most of the day, unfortunately, but a couple of us still went on a very nice hike from Rigi Scheidegg across to and over the top of Rigi Hochflueh with a beautiful view down on the Lucerne Lake and the Rütli Meadow. In the evening, we also tested how many people can be shoehorned into a wood-heated hot tub outside in snow and rain, among other interesting pastimes. Sunday I went climbing with Angela. Considering the rain from the day before and the night and it still being quite cloudy on Sunday, we were maybe the only two crazy enough to even try it. It involved the same walk from Scheidegg to Hochflueh, then searching for the climbing area, doing the climbs, and, last but not least, getting back again safely. The climbing area is called Thedys Gärtli and is on the Hochflue slabs close to the summit, so we could all the time enjoy the same beautiful view as the day before. We were extremely pleased to be able to do two very nice climbs, among the easier ones, Männertrü (4c) and Fürlinie (5c). Although we knew when we started the latter one that we would get back rather late, we actually ended up descending the mountain in total darkness and spending most of the night trying to get back to civilisation. Or, rather, all of the night, since I missed the last train out of there.

Anyway, meanwhile, our inexorable exploration of the Revit API continues, and here is another question to address which expands on our analysis of the calculation of the azimuth or Revit elements:

Question: I am using the Element.Location property to query the X and Y coordinate values of an element. I also make use of the project location and project angle. I have a problem if the Project North has been rotated. How can I determine the 'real' X and Y coordinates of an element if the Project North has been rotated?

Answer: Ok, I see what you mean.

To dive into this a little bit deeper, I implemented a new Building Coder sample command CmdUnrotateNorth to calculate the coordinates of the original unrotated element location for you. It transforms the element location back to the original coordinates to cancel effect of rotating the project north by simply determining the project north rotation angle 'a' and applying a similar transformation to the element coordinates like this:

  Transform t = Transform.get_Rotation(
    XYZ.Zero, XYZ.BasisZ, a );

To simplify testing, I implemented a helper method GetElementLocation which defines a location point for any given element having a non-null Location property:

bool GetElementLocation(
  out XYZ p,
  Element e )
{
  p = XYZ.Zero;
  bool rc = false;
  Location loc = e.Location;
  if( null != loc )
  {
    LocationPoint lp = loc as LocationPoint;
    if( null != lp )
    {
      p = lp.Point;
      rc = true;
    }
    else
    {
      LocationCurve lc = loc as LocationCurve;

      Debug.Assert( null != lc,
        "expected location to be either point or curve" );

      p = lc.Curve.get_EndPoint( 0 );
      rc = true;
    }
  }
  return rc;
}

In the main method, I check that one single element is selected and then list its location point as returned by the API, or rather by this method. I then iterate over all project locations, print each one's the project north angle and list the element location point rotated around the origin by that angle.

I tested this by selecting an element and running the command with it in its original unrotated position, which returns:

Selected element location: (-23.64,1.64,0)
Angle between project north and true north: 0 degrees
Unrotated element location: (-23.64,1.64,0)

After applying a rotation to the project north by calling Manage > Project Location > Position > Rotate Project North > Align selected line or plane, invoking the same command again returns the following:

Selected element location: (-21.66,9.62,0)
Angle between project north and true north: 20 degrees
Unrotated element location: (-23.64,1.64,0)

As you can see, the element location returned by the API is different, but the original value can easily be obtained by applying the rotation described.

Here is the code of the entire mainline of the sample command in its Execute method:

Application app = commandData.Application;
Document doc = app.ActiveDocument;

ElementSet els = doc.Selection.Elements;

if( 1 != els.Size )
{
  message = "Please select a single element.";
}
else
{
  ElementSetIterator it = els.ForwardIterator();
  it.MoveNext();

  Element e = it.Current as Element;

  XYZ p;
  if( !GetElementLocation( out p, e ) )
  {
    message
      = "Selected element has no location defined.";

    Debug.Print( message );
  }
  else
  {
    string msg
      = "Selected element location: "
      + Util.PointString( p );

    double pna = 0;

    foreach( ProjectLocation location
      in doc.ProjectLocations )
    {
      ProjectPosition projectPosition
        = location.get_ProjectPosition( XYZ.Zero );

      pna = projectPosition.Angle;

      msg +=
        "\nAngle between project north and true north: "
        + Util.AngleString( pna );

      Transform t = Transform.get_Rotation(
        XYZ.Zero, XYZ.BasisZ, pna );

      msg +=
        "\nUnrotated element location: "
        + Util.PointString( t.OfPoint( p ) );

      Util.InfoMsg( msg );
    }
  }
}
return IExternalCommand.Result.Failed;

Here is version 1.1.0.50 of the complete Building Coder sample source code and Visual Studio solution including the new command.

Room Boundary Location

We already had a look at enabling the room volume computation in C#. Here is a closely related question that also prompted me to implement something similar in VB for a change.

Question: Could you please provide some VB.NET code showing how to set the Autodesk.Revit.Rooms.BoundaryLocationType in the document, for instance to 'WallCenter'?

Answer: The boundary location type is applied when calculating the room volume. These settings are defined by the document settings volume calculation options. The post mentioned above discusses how to access and modify these settings.

I implemented a VB.NET sample application RoomBoundaryLocation for you to demonstrate this in VB as well. Here is the mainline code of its Execute method:

Public Function Execute( _
  ByVal commandData As ExternalCommandData, _
  ByRef message As String, _
  ByVal elements As ElementSet) _
  As CmdResult _
  Implements IExternalCommand.Execute

  Dim app As Application = commandData.Application
  Dim doc As Document = app.ActiveDocument

  Dim opt As VolumeCalculationOptions _
    = doc.Settings.VolumeCalculationSetting _
      .VolumeCalculationOptions

  opt.VolumeComputationEnable = True

  opt.RoomAreaBoundaryLocation _
    = Rooms.BoundaryLocationType.WallCenter

  doc.Settings.VolumeCalculationSetting _
    .VolumeCalculationOptions = opt

  Dim volumes As List(Of String) = New List(Of String)
  Dim els As ElementSet = doc.Selection.Elements

  Dim e As Autodesk.Revit.Element
  For Each e In els
    If TypeOf e Is Room Then
      Dim room As Room = CType(e, Room)
      volumes.Add(room.Volume.ToString("0.##"))
      'Else
      '  volumes.Add("Not a room")
    End If
  Next

  If 0 = volumes.Count Then
    message = "Please select some rooms."
  Else
    Dim s As String = _
      +"Selected room volumes in cubic feet: " _
      + String.Join(", ", volumes.ToArray()) _
      + "."
    MsgBox(s)
  End If

  Return CmdResult.Failed
End Function

Here are some sample rooms and spaces selected in the Revit user interface:

This is the resulting dialogue displayed by running the command:

Here is the complete Visual Studio solution RoomBoundaryLocation implementing the new command.

Duplicate Family Solids

Here is a question handled by Joe Ye on multiple occurrences of solids in a pipe family definition.

Question: We were surprised to discover that the solids inside a pipe family are duplicated. This is an issue for us, because we want to determine the relationship between the family symbol and the corresponding geometrical solid. We would like to add symbol properties such as a subcategory to the solid. During the export, we don't know which sub category is used for presentation on the screen. We retrieve all the solids, but their subcategory is not defined, so we cannot determine whether or not to export the data.

Answer: There are three solids in the family definition, and they represent three different parts of the pipe. One is for the pipe fitting insulation, another is for the pipe fitting lining, and the third for the pipe itself.

If the parameter values Lining Thickness and Insulation Thickness are zero, all three solids are identical. Otherwise, their sizes are different. Here is an example displaying non-zero Lining Thickness and Insulation Thickness parameter values:

According to which solid you need to export, you can compare the sizes and export only the one that you require.

For example, if you only want to export the insulation size, then you can search for the largest solid and export that. If you want to export the lining solid, export the smallest solid.

If the Lining Thickness and Insulation Thickness are both zero, then exporting any one of them will work.

By the way, for a pipe fitting, there are only two such solids.

Many thanks to Joe for this explanation!

Remove all Geometry from a Family

Here is a question from Joel Karr of Environmental Systems Design, Inc that nicely complements the issue of identifying model elements in a project file with the subsequent correction added.

Question: Is it possible to delete all geometry from a Revit RFA family file? I would like to keep all parameters but delete all geometry.

Answer: To achieve what you desire, we first need to identify all elements contributing geometry to the model, similarly to the model element selection issues mentioned above.

This is simpler in a family file than in a project file, since there are normally less elements and almost all elements having geometry are the ones we are interested in.

I implemented a sample application RemoveRfaGeom to test this, with the following mainline code for its Execute method:

public IExternalCommand.Result Execute( 
  ExternalCommandData commandData, 
  ref string message, 
  ElementSet elements )
{
  Application app = commandData.Application;
  Document doc = app.ActiveDocument;
 
  ElementIterator it = doc.Elements;
  Options opt = app.Create.NewGeometryOptions();
  List<Element> a = new List<Element>();
 
  while( it.MoveNext() )
  {
    Element e = it.Current as Element;
 
    if( null != e.get_Geometry( opt ) )
    {
      a.Add( e );
    }
  }
 
  int n = a.Count;
  Debug.Print( 
    "{0} element{1} have non-null geometry{2}", 
    n, 
    ( 1 == n ? "" : "s" ),
    ( 0 == n ? "." : ":" ) );
 
  ElementSet els = new ElementSet();
 
  foreach( Element e in a )
  {
    string cat = (null == e.Category)
      ? "<null>"
      : e.Category.Name;
 
    Debug.Print(
      "Category={0}; Name={1}; Id={2}; Type={3}",
      cat,
      e.Name,
      e.Id.Value.ToString(),
      e.GetType().Name );
 
    if( null == e.Category )
    {
      els.Insert( e );
    }
  }
 
  ElementIdSet ids = doc.Delete( els );
 
  n = (null == ids) ? 0 : ids.Size;
 
  Debug.Print( "{0} element{1} deleted.",
    n,
    ( 1 == n ? "" : "s" ) );
 
  return IExternalCommand.Result.Succeeded;
}

It performs the following steps, assuming that the active document is indeed a family document:

• Iterate over all family document elements.
• Identify and list all elements with non-null geometry.
• Create a set of all elements with geometry whose category is null.
• Delete the latter set and display the number of deleted elements.

Running this in the metric library rectangular column family file 'M_Rectangular Column.rfa' produces the following output:

2 elements have non-null geometry:
Category=; Name=Extrusion; Id=105; Type=Extrusion
Category=Cameras; Name=View 1; Id=427; Type=Element
13 elements deleted.

As you can see from this, there are some elements having geometry that you presumably do not want to eliminate, such as the camera, so you will need to remove those from the set before deletion. In this case, I simply noted that the camera has a non-null category, whereas the category of the extrusion I want to remove is null, so I just check the null category property to select the extrusion.

Secondly, deleting an element causes other dependent elements to be deleted also, so even though we just pass in one single extrusion element to the Delete method, a whole group of other elements are eliminated as well. We already discussed and made use of this effect to determine the association between a tag and the tagged element and between a host and its hosted elements.

Here is the complete Visual Studio solution RemoveRfaGeom implementing the new command.

Elevation and Section Views

Here are some questions handled by Joe Ye, on creation of and line work in elevation views and the cut plane definition of a section view.

Question: There are different specialised kinds of views derived from the Autodesk.Revit.Elements.View class, and I see several methods in the Revit API to create some of these, such as 3D, Plan, Section, Sheet and Drafting. However, I cannot find a method to create an Elevation View. How can I do that?

Answer: Unfortunately, the Revit API currently does not provide any method to create an elevation view. At the moment, you can use the NewViewSection method to create a vertical section view very similar to an elevation view. By using a large bounding box which does not intersect with the building model, it can display the same view as an elevation view:

Question: Once I have created an elevation view, how would I change the line work of certain elements in that view? In the user interface, Revit provides the Linework tool in the ribbon for this action. How can I achieve this through the API?

Answer: As regards modifying the line work displayed in an elevation view, you can use the CutLinePatternOverrideByElement method on the View object to set the line weight for specified elements. For more information about this method, please see the Revit API help file RevitAPI.chm file in SDK.

Question: How can I get the cut plane definition from a section view programmatically? I just need any point inside the cut plane and the normal vector of the plane to continue to do some other calculations.

Answer: The section view class provides the properties you need. The Origin property of a section view is a point in the world coordinate system or WCS located in the cut plane of the section view. The ViewDirection property of a section view returns a WCS vector indicating the direction towards the viewer. You can use the section view Origin as the cut plane origin, and the ViewDirection as its normal vector. Depending to your usage, you might need to reverse the direction of the ViewDirection.

Thank you very much Joe for these answers!

Detail Lines

We previously discussed various aspects of model lines, such as model line creation, the model line sketch plane, and the minimal length of a model line. Here is a question on the related topic of detail lines handled by my colleague Saikat Bhattacharya:

Question: How can I create a detail line on a drafting view? I tried to use the following statement:

doc.Create.NewDetailCurve( View, curve, y );

It is unclear to me what the "curve" and the "sketchPlane" stand for and how to use them. Please could you provide me with a small sample.

Answer: Detail curves are created for drawings such as a detail or drafting view. They are annotation elements and are visible only in the view in which they are drawn. They can currently only be created in plan views.

Except for this, detail curves are similar to model curves. ModelLine and DetailLine both belong to the Lines category. Thus, for a sample on creating detail curves, you can refer to and slightly adapt the Revit SDK sample ModelLines, which shows how to work with the sketch plane and geometry curve to create a new model line.

For more details on sketch planes and model curves, you can also refer to the developer guide "Revit 2010 API Developer Guide.pdf", especially chapter 14, Annotation Elements, and section 14.2, Detail Curve. Another helpful section is 15.3.1 on Creating a ModelCurve and the Code Region 15-2: Creating a new model curve, which illustrates how to create new geometry curves, a sketch plane, and model curves, a ModelLine and a ModelArc. You can use the same approach to create detail curves as well.

I implemented a new external command CmdDetailCurves in The Building Coder sample application by slightly modifying the sample code provided in the developer guide. Here is the code of the new command's Execute method:

  Application app = commandData.Application;
  Document doc = app.ActiveDocument;
  View view = doc.ActiveView;
 
  // Create a geometry line
  XYZ startPoint = new XYZ( 0, 0, 0 );
  XYZ endPoint = new XYZ( 10, 10, 0 );
 
  Line geomLine = app.Create.NewLine(
    startPoint, endPoint, true );
 
  // Create a geometry arc
  XYZ end0 = new XYZ( 1, 0, 0 );
  XYZ end1 = new XYZ( 10, 10, 10 );
  XYZ pointOnCurve = new XYZ( 10, 0, 0 );
 
  Arc geomArc = app.Create.NewArc(
    end0, end1, pointOnCurve );
 
  // Create a geometry plane
  XYZ origin = new XYZ( 0, 0, 0 );
  XYZ normal = new XYZ( 1, 1, 0 );
 
  Plane geomPlane = app.Create.NewPlane(
    normal, origin );
 
  // Create a sketch plane in current document
  SketchPlane sketch = doc.Create.NewSketchPlane(
    geomPlane );
 
  // Create a DetailLine element using the 
  // created geometry line and sketch plane
  DetailLine line = doc.Create.NewDetailCurve(
    view, geomLine ) as DetailLine;
 
  // Create a DetailArc element using the 
  // created geometry arc and sketch plane
  DetailArc arc = doc.Create.NewDetailCurve(
    view, geomArc ) as DetailArc;
 
  return CmdResult.Succeeded;

As you see, the curve parameter above can be any geometric curve entity like Line, Arc, Ellipse or NurbSpline. All of these types are derived from the Curve class and can be used as parameters to create a detail curve.

Here are the resulting detail curves after running this command in a new project document:

Here is version 1.1.0.46 of the complete Building Coder sample source code and Visual Studio solution including the new command.

Thank you Saikat for this helpful explanation!

Creating a Non-rectangular Slab

Here is a question raised and answered by my colleagues Katsuaki Takamizawa and Phil Xia on creating and editing a slab. Some related topics that we already discussed are related to the analysis of the geometry of existing slabs, e.g. the slab boundary and its side faces, explorations of the geometry of other elements, the eave cut property of roof slabs, and how to edit a floor profile. Now let's look at this generic slab issue:

Question: In the user interface, we can use the shape editing tools to modify slab surfaces and to create non-rectangular slabs. Is it possible to create slabs like these through the API as well?

Also, can we define slope angles on these non-rectangular slabs?

Answer: You can modify the slab surface with the slab editor, accessible through the SlabShapeEditor property on the Floor class. The SDK sample SlabShapeEditing shows how to use it.

There is no way to modify the slope of an existing slab, but it can be specified when a new slab is created with NewSlab method:

public Floor NewSlab(
  CurveArray profile,
  Level level,
  Line slopedArrow,
  double slope,
  bool isStructural
)

The parameters are:

• profile: an array of planar lines and arcs that represent the horizontal profile of the slab.
• level: the level on which the slab is to be placed.
• slopedArrow: a line to control the sloped angle of the slab. It should be in the same face as the profile.
• slope: defines the slope.
• isStructural: specifies whether the slab is structural.

Many thanks to Phil and Katsu-san for this overview!

New Sweep and References

Here is a question posted by Mike Cotreau of Langan Engineering & Environmental Services on how to create a new sweep using a reference array, which provided a welcome opportunity to explain a little about the use of references in the Revit API:

Question: I want to use the NewSweep method to create a 3D curb line that follows along a path of 3D points. The NewSweep method can be invoked in two ways, one uses a ReferenceArray and the second uses a CurveArray. There is an example provided in the VSTA Family Sample code that illustrates the CurveArray version and I have used that code to layout an entire curbline without issues. Unfortunately, I need to use the first version that allows for a sweep to follow a 3D path using the ReferenceArray version. I keep getting an error saying the object is not referenced, and I am clueless as to why. I am using VB.NET and here is the code I modified from the sample code:

 
Dim arrarr As CurveArrArray = m_revit.Create.NewCurveArrArray()
Dim arr As CurveArray = m_revit.Create.NewCurveArray()
'****** This creates the section for the curb ********
Dim normal As XYZ = XYZ.BasisZ
Dim sketchPlane As SketchPlane = CreateSketchPlane(normal, XYZ.Zero)
Dim pnt1 As XYZ = m_revit.Create.NewXYZ(0, 0, 0)
Dim pnt2 As XYZ = m_revit.Create.NewXYZ(0, 0.5, 0)
Dim pnt3 As XYZ = m_revit.Create.NewXYZ(0.5, 0.5, 0)
Dim pnt4 As XYZ = m_revit.Create.NewXYZ(0.5, -1, 0)
Dim pnt5 As XYZ = m_revit.Create.NewXYZ(0, -1, 0)
arr.Append(m_revit.Create.NewLineBound(pnt1, pnt2))
arr.Append(m_revit.Create.NewLineBound(pnt2, pnt3))
arr.Append(m_revit.Create.NewLineBound(pnt3, pnt4))
arr.Append(m_revit.Create.NewLineBound(pnt4, pnt5))
arr.Append(m_revit.Create.NewLineBound(pnt5, pnt1))
arrarr.Append(arr)
Dim profile As SweepProfile = m_revit.Create.NewCurveLoopsProfile(arrarr)
Dim curves As CurveArray = m_revit.Create.NewCurveArray()
Dim refArray As ReferenceArray = m_revit.Create.NewReferenceArray
Dim pt1 As XYZ = m_revit.Create.NewXYZ(-265.9978, -358.3954, 0)
Dim pt2 As XYZ = m_revit.Create.NewXYZ(-265.9374, -340.4006, 0)
Dim curve As Curve = m_revit.Create.NewLineBound(pt1, pt2)
curves.Append(curve)
refArray.Append(curve.Reference)
'Create the Sweep
Dim sweep1 As Sweep = m_creationFamily.NewSweep(True, refArray, profile, 0, ProfilePlaneLocation.Start)
' move to proper place 
Dim transPoint1 As XYZ = m_revit.Create.NewXYZ(11, 0, 0)
m_familyDocument.Move(sweep1, transPoint1)

An exception is thrown on the NewSweep method. I have also tried building the Reference array using code like this without any luck:

refArray.Append(curve.get_EndPointReference(0))
refArray.Append(curve.get_EndPointReference(1))

Any help you can provide that allows me to sweep along a 3D path would be GREATLY appreciated.

Answer: NewSweep is used in the family document to create a new sweep. The overloads you refer to for creating a new sweep form are:

• NewSweep( Boolean, ReferenceArray, SweepProfile, Int32, ProfilePlaneLocation ), using an array of selected references as a 3D path.
• NewSweep( Boolean, CurveArray, SketchPlane, SweepProfile, Int32, ProfilePlaneLocation ), using a path of curve elements.

The three last arguments are the same for both overloads, so these are presumably not cause of the problem:

• SweepProfile profile,
• int profileLocationCurveIndex, and
• ProfilePlaneLocation profilePlaneLocation.

The API documentation specifies the reference array passed in to define the path in the first overload as follows:

• ReferenceArray path: The path of the sweep. The path should be reference of curve or edge obtained from existing geometry.

The cause of your problem is almost certainly the fact that the curve that you are trying to obtain references from is not part of any existing geometry, since you created it on the fly.

To understand the difference and the importance of this, here are some private hypothetical musings of mine on what references actually mean within Revit. I have never seen any hard documentation of this, but I am gradually getting the following idea:

References

All of objects living in the Revit API Geometry namespace are transient in-memory objects. The non-transient Revit BIM model resides in the database. To query the geometry of BIM objects, transient geometry is generated on the fly from their parametric representations. If a new BIM object B is to be generated and stored in the database, such as your sweep, and it needs to reference existing BIM geometry in any way, for instance some edge of an existing object A, then a reference can be generated to provide a hook from the new object B definition through the transient geometry back to the underlying BIM object A. Later on, when the BIM is saved, the transient geometry has all disappeared, but the reference ensures that B knows that it depends on the geometry and location of A in some way. If A is moved or modified, B can adapt.

In your sample, you are creating a new line between two fixed points pt1 and pt2. This is all transient geometry, and not referring back to any BIM object, so there is no way that the resulting curve can contain or provide a valid reference to anything.

The question is why you are trying to use the overload requiring a reference array at all? If your input data is fixed, you should use the curve array option instead.

By the way, for completeness sake, prompted by your query, I had a look at the VSTA family samples. They are provided in the Revit SDK VSTA Samples sub-folder, in the family file Revit_VSTA_Family_Samples.rfa. I see the code you based yours on, in the subroutine CreateSweep() of the GenericModelCreation project. This project is also provided as one of the standard SDK samples as well, albeit only in a C# version.

I hope this answers your question. Good luck!

Bottom Face of a Wall

We already went into quite a bit of detail analysing the geometry of walls and other elements, but the topic keeps cropping up again anyway. An overview of the preceding posts on this topic is given in the discussion of cylindrical columns. Here is a case handled by Joe Ye which I thought might complement the previous posts on this topic, since it is so simple and minimal.

Question: How can I find the bottom face of a wall?

Answer: We can query the wall for its solid geometry using the Element.Geometry property, which is accessed by the get_Geometry method in C#. From the returned solid, all faces can be accessed. The bottom face of the wall has a normal vector equal to (0,0,-1), and in most cases this is the unique for the bottom face. So we just iterate over all faces, and stop when we find one whose normal is (0,0,-1).

I implemented a new external command named CmdWallBottomFace to demonstrate this. Here is the code of its Execute method. As always, it returns Failed even if it did in fact succeed, so that no changes are registered in the BIM, since the command does nothing to modify the model:

Application app = commandData.Application;
Document doc = app.ActiveDocument;
 
string s = "a wall, to retrieve its bottom face";
 
Wall wall = Util.SelectSingleElementOfType(
  doc, typeof( Wall ), s ) as Wall;
 
if( null == wall )
{
  message = "Please select a wall.";
}
else
{
  Options opt = app.Create.NewGeometryOptions();
  GeoElement e = wall.get_Geometry( opt );
  XYZ vDown = -XYZ.BasisZ;
 
  foreach( GeometryObject obj in e.Objects )
  {
    Solid solid = obj as Solid;
    if( null != solid )
    {
      foreach( Face face in solid.Faces )
      {
        PlanarFace pf = face as PlanarFace;
        if( null != pf )
        {
          if( pf.Normal.Dot( vDown ) < 0.001 )
          {
            Util.InfoMsg( string.Format(
              "The bottom face area is {0},"
              + " and its origin is at {1}.",
              Util.RealString( pf.Area ),
              Util.PointString( pf.Origin ) ) );
            break;
          }
        }
      }
    }
  }
}
return CmdResult.Failed;

When the command is executed and a wall selected, the area and origin point of its bottom face is reported in a message box and in the Visual Studio debug output window:

The bottom face area is 265.82, 
and its origin is at (30.76,20.57,-9.84).

Here is version 1.1.0.44 of the complete Visual Studio solution including the new command.

Thank you very much Joe for this answer!