acad-dimensions

name	acad-dimensions
description	Dimensions — aligned, rotated, arc, radial, angular, ordinate, text overrides

AutoCAD Dimensions

Use this skill when creating or modifying dimension objects - linear, aligned, angular, radial, diametric, arc, and ordinate dimensions, plus dimension styles.

Dimension Class Hierarchy

Dimension (abstract base)
├── AlignedDimension
├── RotatedDimension
├── ArcDimension
├── DiametricDimension
├── RadialDimension
├── LineAngularDimension2
├── Point3AngularDimension
└── OrdinateDimension

Creating Dimensions

Aligned Dimension

AlignedDimension dim = new AlignedDimension(
    new Point3d(0, 0, 0),      // first extension line point
    new Point3d(100, 0, 0),    // second extension line point
    new Point3d(50, 20, 0),    // dimension line position
    "",                         // dimension text (empty = measurement)
    db.Dimstyle);              // dimension style ObjectId

btr.AppendEntity(dim);
tr.AddNewlyCreatedDBObject(dim, true);

Rotated Dimension

RotatedDimension dim = new RotatedDimension(
    0.0,                        // rotation angle (radians)
    new Point3d(0, 0, 0),      // first extension line point
    new Point3d(100, 50, 0),   // second extension line point
    new Point3d(50, 70, 0),    // dimension line position
    "",                         // dimension text
    db.Dimstyle);

Arc Dimension

ArcDimension dim = new ArcDimension(
    new Point3d(50, 50, 0),    // center point
    new Point3d(100, 50, 0),   // first extension line point
    new Point3d(50, 100, 0),   // second extension line point
    new Point3d(80, 80, 0),    // arc point (dimension position)
    "",                         // dimension text
    db.Dimstyle);

Radial Dimension

RadialDimension dim = new RadialDimension(
    new Point3d(50, 50, 0),    // center point
    new Point3d(100, 50, 0),   // chord point (on circle)
    10.0,                       // leader length
    "",                         // dimension text
    db.Dimstyle);

Diametric Dimension

DiametricDimension dim = new DiametricDimension(
    new Point3d(100, 50, 0),   // chord point (near side)
    new Point3d(0, 50, 0),     // far chord point (opposite side)
    10.0,                       // leader length
    "",                         // dimension text
    db.Dimstyle);

Angular Dimension (2-Line)

LineAngularDimension2 dim = new LineAngularDimension2(
    new Point3d(0, 0, 0),      // first line start
    new Point3d(100, 0, 0),    // first line end
    new Point3d(0, 0, 0),      // second line start
    new Point3d(0, 100, 0),    // second line end
    new Point3d(30, 30, 0),    // arc point (dimension position)
    "",                         // dimension text
    db.Dimstyle);

Angular Dimension (3-Point)

Point3AngularDimension dim = new Point3AngularDimension(
    new Point3d(50, 50, 0),    // center point (vertex)
    new Point3d(100, 50, 0),   // first point on angle
    new Point3d(50, 100, 0),   // second point on angle
    new Point3d(80, 80, 0),    // arc point (dimension position)
    "",                         // dimension text
    db.Dimstyle);

Ordinate Dimension

OrdinateDimension dim = new OrdinateDimension(
    true,                       // true = X axis, false = Y axis
    new Point3d(100, 50, 0),   // defining point
    new Point3d(100, 80, 0),   // leader end point
    "",                         // dimension text
    db.Dimstyle);

Dimension Styles

DimStyleTable dst = (DimStyleTable)tr.GetObject(
    db.DimStyleTableId, OpenMode.ForWrite);

DimStyleTableRecord dstr = new DimStyleTableRecord();
dstr.Name = "MyDimStyle";

// Text settings
dstr.Dimtxt = 2.5;           // text height
dstr.Dimtxsty = textStyleId;  // text style
dstr.Dimgap = 1.0;           // text gap
dstr.Dimtad = 1;             // text above (0=centered, 1=above)

// Arrow settings
dstr.Dimasz = 2.5;           // arrow size
dstr.Dimtsz = 0.0;           // tick size (0 = use arrows)

// Line settings
dstr.Dimexe = 1.25;          // extension line extension
dstr.Dimexo = 0.625;         // extension line offset

// Scale
dstr.Dimscale = 1.0;         // overall scale

// Units
dstr.Dimdec = 2;             // decimal places
dstr.Dimlunit = 2;           // decimal (2=Decimal, 4=Architectural)

ObjectId styleId = dst.Add(dstr);
tr.AddNewlyCreatedDBObject(dstr, true);

// Apply style to a dimension
dim.DimensionStyle = styleId;

Gotchas

• Empty string "" for DimensionText shows the measured value; use "<>" to embed the measurement within custom text (e.g., "Length: <> mm")
• All Dim* properties on a Dimension entity are per-entity overrides - they only take effect when they differ from the dimension style
• Use SetDimstyleData() to apply all dim variable overrides from a style at once; individual property sets only override specific variables
• Measurement is read-only and computed from geometry points - move the points to change the measurement
• RecomputeDimensionBlock(true) must be called after changing geometry points programmatically for the visual to update
• Angular dimensions measure the angle on the side where ArcPoint is placed - the arc point determines which of the four possible angles is measured
• DimStyleTableRecord.Dimtxsty is the text style; Dimension.TextStyleId is the same thing but with a friendlier name
• Dimblk sets both arrows; use Dimblk1/Dimblk2 with Dimsah = true for separate arrow heads
• Ordinate dimensions: UsingXAxis = true measures X coordinates, UsingXAxis = false measures Y coordinates
• GetDimstyleData() returns a temporary DimStyleTableRecord not owned by the database — call Dispose() on it after use to avoid memory leaks: using (var tmp = dim.GetDimstyleData()) { ... }
• DimStyleTableRecord.CopyFrom(sourceDstr) copies all dim variable values but overwrites the Name property — reassign dstr.Name immediately after calling CopyFrom()

Related Skills

• acad-geometry — Point3d coordinates for dimension definition points
• acad-mtext — MText formatting in dimension text overrides
• acad-layers — layer assignment for dimension entities