GeometryHelper.CadConvert

NuGet Version License: MIT

Converts geometry between AutoCAD and GeometryHelper, both ways: points, vectors, line segments and Line entities, polylines and polygons with the arcs their bulges draw, arcs, circles, and Extents2d/Extents3d as rectangles.

Installation

dotnet add package GeometryHelper.CadConvert

You must add the AutoCAD assemblies yourself

This package does not contain any AutoCAD assembly. They are Autodesk's to distribute rather than ours, so it ships only its own code and leaves those references to you. Until you add them, code that touches this library fails to compile with CS0012: the type is defined in an assembly that is not referenced.

The library itself resolves against acdbmgd.dll alone — that is where Point3d, Polyline, Circle, Line and Extents3d live. A plugin normally also wants acmgd.dll and accoremgd.dll for the editor and application APIs, so all three are shown below.

Take them from either source:

From your AutoCAD installation — the usual choice, because it guarantees you build against the same version you run:

<Reference Include="accoremgd">
  <HintPath>C:\Program Files\Autodesk\AutoCAD 2024\accoremgd.dll</HintPath>
  <Private>false</Private>
</Reference>
<Reference Include="acdbmgd">
  <HintPath>C:\Program Files\Autodesk\AutoCAD 2024\acdbmgd.dll</HintPath>
  <Private>false</Private>
</Reference>
<Reference Include="acmgd">
  <HintPath>C:\Program Files\Autodesk\AutoCAD 2024\acmgd.dll</HintPath>
  <Private>false</Private>
</Reference>

Or from Autodesk's own package on nuget.org:

dotnet add package AutoCAD.NET

Keep Copy Local false. AutoCAD supplies those assemblies at run time from its own installation, and a copy sitting next to your plugin risks loading a build that does not match the running AutoCAD.

Which AutoCAD version

The package is built against the AutoCAD 2024 API (assembly version 24.0.0.0). Autodesk keeps the Autodesk.AutoCAD.Geometry and Autodesk.AutoCAD.DatabaseServices types this library touches stable across releases, so building from source against another version needs no source changes.

AutoCAD.NET on nuget.org carries no netstandard2.0 assets — version 24–25 ship net47 and version 26 ships net10.0 — so a project taking that dependency has to target the framework matching the AutoCAD it runs in. Referencing the DLLs directly, as above, avoids that constraint.

Usage

using Autodesk.AutoCAD.DatabaseServices;
using Autodesk.AutoCAD.Geometry;
using GeometryHelper.CadConvert;
using GeometryHelper.Geometry;

// AutoCAD to GeometryHelper
GeoPoint2 point = new Point3d(100, 200, 0).ToGeoPoint2();
GeoPolyline2 path = acadPolyline.ToGeoPolyline2();
GeoRectangle2 bounds = extents.ToGeoRectangle2();
GeoCircle2 circle = acadCircle.ToGeoCircle2();

// GeometryHelper back to AutoCAD
Polyline drawn = path.ToAcadPolyline();
Line drawnLine = geoLine.ToAcadLine();
Point3d back = point.ToAcadPoint3();

Point chains

EnumerableExtension covers the step before a polyline exists: a raw list of points read out of a drawing, usually carrying more of them than the geometry needs.

// Drop points that sit within the tolerance of the point kept before them.
List<Point3d> thinned = points.RemoveConsecutiveNearPoints(0.5);

// One segment per consecutive pair; the chain is left open.
List<LineSegment3d> segments = thinned.ToLineSegments3d();

LineSegment3d longest = segments.GetLongestLength();

RemoveConsecutiveNearPoints compares each point against the last one kept, not against its original neighbour, which is what guarantees no two points of the result are within the tolerance of each other. The first point always survives; the last one is not privileged, so re-append it yourself when the endpoint matters.

Arcs and bulges

An AutoCAD polyline carries a bulge against each vertex, and a vertex with a bulge is joined to the next one by an arc. Reading such a polyline as points alone used to straighten it silently, so a slot came back a rectangle. It no longer does.

// Keeps every arc: the bulge AutoCAD stores is the bulge GeometryHelper stores.
GeoPolylineArc2 chain = acadPolyline.ToGeoPolylineArc2();
GeoPolygonArc2 loop   = acadPolyline.ToGeoPolygonArc2();

// Cuts the arcs into straight pieces, within 0.2 % of each radius, and says so in GeometryHelperLog.
GeoPolyline2 path = acadPolyline.ToGeoPolyline2();
GeoPolygon2 area  = acadPolyline.ToGeoPolygon2(0.05);   // or name the chord tolerance yourself

// Refuses rather than approximates, for a caller that needs the shape exactly.
if (acadPolyline.TryToGeoPolygon2(out GeoPolygon2 exact)) { ... }

// And back, bulge for bulge; the loop comes back closed.
Polyline drawnChain = chain.ToAcadPolyline();
Polyline drawnLoop  = loop.ToAcadPolyline();

ToGeoPolyline2 and ToGeoPolygon2 still return the straight types they always did, so nothing that used them has to change — they now trace the arc instead of cutting across it. Work on the shape with the whole of GeometryHelper, then write it back:

GeoPolygonArc2 rounded = acadPolyline.ToGeoPolygonArc2().Fillet(25.0);
acadPolyline.Erase();
blockTable.AppendEntity(rounded.ToAcadPolyline());

The Arc and Circle entities convert on their own too:

GeoArc2 flat = acadArc.ToGeoArc2();     // in plan; throws if the arc is tilted out of XY
GeoArc3 real = acadArc.ToGeoArc3();     // whatever plane it lies in
acadArc.TryToGeoArc2(out GeoArc2 read); // false rather than throwing

Arc drawn = flat.ToAcadArc();
Circle hole = new GeoCircle2(center, 12.5).ToAcadCircle();

An AutoCAD arc always sweeps counter-clockwise about its normal and has nowhere to put a direction of its own, so a clockwise GeoArc2 is written with its two angles exchanged: the same curve, read back counter-clockwise.

Licence

MIT. The AutoCAD assemblies this library compiles against are covered by Autodesk's own licence terms, not by this one.

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