Doesn't get the minimal bounding box from the solid of the structural column

[yuvdal]

Hello,

I am trying to get the bounding box from the solid of structural column but unfortunately, I don't get the minimal one.

In order to demonstrate it, I modeled in-place the following structural column:

Then I tried to run the following function that gets the bounding boxes from all the solids and merges them. In order to show the result, I display the bounding box.

            // Application context
            var uidoc = commandData.Application.ActiveUIDocument;
            var doc = uidoc.Document;

            var selectionReference = uidoc.Selection.PickObject(ObjectType.Element);
            var selectionElement = doc.GetElement(selectionReference);

            //Override the options to use Fine detail level
            List<BoundingBoxXYZ> solidsBoundingBoxes = new List<BoundingBoxXYZ>();

            Options options = new Options { ComputeReferences = true, DetailLevel = ViewDetailLevel.Fine };
            GeometryElement geometryElement = selectionElement.get_Geometry(options);

            foreach (GeometryObject geomObject in geometryElement)
            {
                // You can obtain wall solid with method in the top but some other elements need this type conversion
                if (geomObject is GeometryInstance geomInst)
                {
                    // Instance geometry is obtained so that the intersection works as
                    // expected without requiring transformation
                    GeometryElement instElem = geomInst.GetInstanceGeometry();
                    foreach (GeometryObject instObj in instElem)
                    {
                        if (instObj is Solid innerSolid)
                        {
                            if (innerSolid.Volume > 0)
                            {
                                BoundingBoxXYZ boundingBox = new BoundingBoxXYZ();

                                XYZ bBoxOrigin = innerSolid.GetBoundingBox().Transform.Origin;

                                boundingBox.Max = innerSolid.GetBoundingBox().Max + bBoxOrigin;
                                boundingBox.Min = innerSolid.GetBoundingBox().Min + bBoxOrigin;

                                solidsBoundingBoxes.Add(boundingBox);
                            }
                        }
                    }
                }
            }

            //Get the surrounding bounding boxes that were collected by finding the lowest min point and highest max point
            BoundingBoxXYZ surroundingBoundingBox = GetBoundingBoxUtils.GetSurroundingBoundingBox(solidsBoundingBoxes);

            // Display the Merged Bounding Box from the Solids
            var elem = DisplayUtils.DisplayBoundingBox(surroundingBoundingBox);

The problem is that the bounding box that I get from the solids is not the minimal one. There is an offset of 1/16" from each side of the structural column.

I'm trying to figure out what I'm missing, because for comparison when I run a similar graph in Dynamo, it shows me the correct bounding box from the solids.

I would be glad if someone could help me understand what the difference is between what I do in the code and the Dynamo graph.

Thanks a lot,

Yuval

[jeremy_tammik]

Dear Yuval,

You seem to be repeating the same question I already answered in this previous recent thread:

• Get bounding box from solid of a structural column is not accurate -- https://forums.autodesk.com/t5/revit-api-forum/get-bounding-box-from-solid-of-a-structural-column-is...

Remember: a bounding box is a bounding box. There is no guarantee that a bounding box is minimal. Never.

The main purpose of a bounding box is speed, not accuracy, and definitely not to be minimal.

Since you can never assume that a bounding box is minimal, and if this is causing an issue with your code, I would recommend checking whether is is erroneously making this assumption. If it is, it might be safer to fix it.

If your application requires a minimal bounding box, the safest way to obtain it is to query the element geometry for all its vertices and create a convex hull or truly minimal bounding box from those.

I described an approach to retrieve the element geometry vertices in this other recent discussion:

• Face Vertex -- https://forums.autodesk.com/t5/revit-api-forum/face-vertex/m-p/11201131

I would create a list of unique values while iterating over all the face vertices. The Building Coder demonstrates several variations of this with methods such as GetVertices in CmdNestedInstanceGeo.cs:

• https://github.com/jeremytammik/the_building_coder_samples
• https://github.com/jeremytammik/the_building_coder_samples/blob/master/BuildingCoder/CmdNestedInstan...

I hope this clarifies.

Best regards,

Jeremy