Revit Plugin Development: Automated Grid Alignment Made Easy

During project development, meshes are often flipped or selected incorrectly, resulting in unattractive meshes. To address this, a mesh alignment feature has been added. Let’s dive straight into the practical details.

First, some preparation is needed. Create a mesh filtering class, which will be used later. Here is the code:

class GridSelectionFilter : ISelectionFilter
{
    public bool AllowElement(Element element)
    {
        int idValue = element.Category.Id.IntegerValue;
        if (idValue == (int)BuiltInCategory.OST_Grids)
        {
            return true;
        }
        return false;
    }

    public bool AllowReference(Reference reference, XYZ position)
    {
        return false;
    }
}

Next, here is the core grid alignment implementation:

// Create a new grid selection filter
GridSelectionFilter gridSelectionFilter = new GridSelectionFilter();

// Select grids within a frame
IList<Element> selectedGrids = sel.PickElementsByRectangle(gridSelectionFilter, "Select grids");

// Pick a point to serve as the alignment reference
XYZ alignmentPoint = sel.PickPoint("Please select an alignment point");

// Start a transaction to modify grids
Transaction transaction = new Transaction(doc);
transaction.Start("Modify grids");

if (selectedGrids.Count > 1)
{
    foreach (Element elem in selectedGrids)
    {
        Grid grid = elem as Grid;
        Line line = grid.Curve as Line;
        XYZ start = line.GetEndPoint(0);
        XYZ end = line.GetEndPoint(1);

        // Determine which endpoint is closer to the selected alignment point
        double distanceToEnd = alignmentPoint.DistanceTo(end);
        double distanceToStart = alignmentPoint.DistanceTo(start);

        if (distanceToEnd < distanceToStart)
        {
            // End point is closer
            XYZ vectorToPoint = new XYZ(alignmentPoint.X - end.X, alignmentPoint.Y - end.Y, alignmentPoint.Z - end.Z);
            double distance = Math.Sqrt(vectorToPoint.X * vectorToPoint.X + vectorToPoint.Y * vectorToPoint.Y + vectorToPoint.Z * vectorToPoint.Z);

            // Calculate angle between grid direction and vector to alignment point
            double angle = line.Direction.AngleTo(vectorToPoint);

            // Calculate new end point coordinates
            XYZ newEnd = start + (line.Length + distance * Math.Cos(angle)) * line.Direction;

            // Create a new grid line with the updated endpoint
            Line newLine = Line.CreateBound(start, newEnd);
            Grid newGrid = Grid.Create(doc, newLine);
            string originalName = grid.Name;

            // Delete the old grid and assign the original name to the new one
            doc.Delete(grid.Id);
            newGrid.Name = originalName;
        }
        else
        {
            // Start point is closer
            XYZ vectorToPoint = new XYZ(alignmentPoint.X - start.X, alignmentPoint.Y - start.Y, alignmentPoint.Z - start.Z);
            double distance = Math.Sqrt(vectorToPoint.X * vectorToPoint.X + vectorToPoint.Y * vectorToPoint.Y + vectorToPoint.Z * vectorToPoint.Z);

            // Calculate angle between grid direction and vector to alignment point
            double angle = line.Direction.AngleTo(vectorToPoint);

            // Calculate new start point coordinates
            XYZ newStart = end - (line.Length - distance * Math.Cos(angle)) * line.Direction;

            // Create a new grid line with the updated start point
            Line newLine = Line.CreateBound(newStart, end);
            Grid newGrid = Grid.Create(doc, newLine);
            string originalName = grid.Name;

            // Delete the old grid and assign the original name to the new one
            doc.Delete(grid.Id);
            newGrid.Name = originalName;
        }
    }
}

transaction.Commit();

The code above provides a basic approach to grid alignment. If you find any errors or have suggestions for improvements, feel free to leave a comment!

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