CADSoftTools

Posted: **12 May 2006, 13:54**

Hi,

There is a case where the angle of the Insert circular arc of SimpleImport reverses.

<b>procedure</b> TForm1.ReadCADEntities(Entity: TsgDXFEntity);
<b>var</b>
.....
<b>begin</b>
  C := EntColor(Entity, FCADParams.Insert);
  L := EntStyle(Entity);
  
  <b>if</b> Entity <b>is</b> TsgDXFArc <b>then
    begin</b>
      P := PtXMat(TsgDXFArc(Entity).Point, FCADParams.Matrix);
      sa := TsgDXFArc(Entity).StartAngle;
      ea := TsgDXFArc(Entity).EndAngle;

      <b>if</b> FCADParams.Insert <> <b>nil then
        if</b> FCADParams.Insert.Angle <> 0.0 <b>then
          begin</b>
            sa := sa + FCADParams.Insert.Angle;
            ea := ea + FCADParams.Insert.Angle;
          <b>end</b>;

      <b>while</b> sa > ea <b>do</b> sa:=sa-360.0;

      DB_AddArc(P.X, P.Y, TsgDXFArc(Entity).Radius, DegToRad(sa), DegToRad(ea), L, C);
    <b>end</b>;
<b>end</b>;

What is the problem?

Posted: **18 May 2006, 19:40**

Hello,

If an ARC entity is located inside a block or has an extrusion, then this ARC can't be represented in planar view if it had not earlier been converted into polyline.
All CAD systems can draw an ARC as a polyline. So what you need to do is:
1) to get the transformation matrix (FCADParams.Matrix),
2) to brake the ARC into linear sections (defined by a set of points):
{ ConvertsEllipticArcToPolyline
AStart, AEnd angles in radians (AStart=0, AEnd=2*Pi for circle)
A, B - big and small radiuses (A=B for circle)
ASin, ACos - parameters that determine a tilt angle of major semiaxis of the ellipse
( - for TsgDXFEllipse object: ASin= TsgDXFEllipse.RadPt.Y/TsgDXFEllipse.Radius and ACos= TsgDXFEllipse.RadPt.X/TsgDXFEllipse.Radius;
- ASin=0, ACos=1 for circle. )

Returns list of points. Please clear this TList after using. }

Code: Select all

<b>function</b> ConvertsEllipticArcToPolyline(Arc: TsgDXFCircle; A, B, ASin, ACos, AStart, AEnd: Double): TList;
<b>const</b>
  cnstNumberPartsInCircle = 36;
<b>var</b>
  X, Y, Delta: Double;
  S, C: Extended;
  I: Integer;
  vPPoint: PFPoint;  
<b>begin</b>
  Result := TList.Create;
  Params(A, B, AStart, AEnd, ASin, ACos);  
  Delta := (AEnd - AStart) / cnstNumberPartsInCircle;
  <b>for</b> I := 0 <b>to</b> cnstNumberPartsInCircle <b>do
  begin</b>
    SinCos(AStart, S, C);
    New(vPPoint);
    X := A * C;
    Y := B * S;
    vPPoint^.X := Point.X + X * ACos - Y * ASin;
    vPPoint^.Y := Point.Y + X * ASin + Y * ACos;
    vPPoint^.Z := Point.Z;
    Result.Add(vPPoint);
    AStart := AStart + Delta;
  <b>end</b>;
<b>end</b>;

3) Do for each point from ConvertsEllipticArcToPolyline list:
vRealPoint := PtXMat(listpoint, FCADParams.Matrix);

Sergey.

please post questions to the forum or write to support@cadsofttools.com

Posted: **23 May 2006, 13:35**

Thank you for answering.

However, the angle is necessary for me.
I want to know whether the direction of drawing is clockwise or opposite, too.

best regards.

Posted: **24 May 2006, 12:30**

Hello,

Commonly this is impossible to get angle. EntArc works correctly only for some private cases and it always sets direction for ARC clockwise (otherwise, it just changes places StartPoint and EndPoint).

Sergey.

please post questions to the forum or write to support@cadsofttools.com

CADSoftTools

Angle of SimpleImport circular arc

Angle of SimpleImport circular arc