topic Re: AcGeCircArc2d problem with tangent function in ObjectARX Forum

AcGeCircArc2d problem with tangent function

mconficconi — Wed, 03 Feb 2016 15:29:41 GMT

AcGePoint2d p2d01(0.73418800649031368,17.848733056886374);

AcGePoint2d p2d02(-61.740762501740704,-4.9277122828104929);

double dBulge=0.19787629562480538;

AcGeCircArc2d ca2dCCW(p2d01, p2d02, dBulge, Adesk::kFalse);

AcGeLine2d l2dTg;

ca2dCCW.tangent(p2d01, l2dTg);

AcGeVector2d v2dDzTg=l2dTG.direction();

v2dDzTg is in the wrong way; the triangle ca2dCCW.center(), p2d01, p2d01+v2dDzTg is clock wise, but the arc is counter clock wise

Is this an error, or i'm not understund how tangent work?

Thank's in advance

Re: AcGeCircArc2d problem with tangent function

tbrammer — Tue, 09 Feb 2016 08:40:47 GMT

I suppose you have been confused by the AcGeCircArc2d object because you didn't consider AcGeCircArc2d::refVec().

The code below shows what I mean. I have renamed your variables for better readability but took the same values.

The function just creates an AcDbArc from the AcGeCircArc2d, an AcDbLine for the tangent and another AcDbLine between the arc's start- and endpoint. Note the value refAng = arc.refVec().angle(). If you don't add this value to the start-/endangle you'll get a misplaced arc!

void cmdTangent()
{
	AcGePoint2d p1(0.73418800649031368,17.848733056886374);
	AcGePoint2d p2(-61.740762501740704,-4.9277122828104929);
	double dBulge = 0.19787629562480538;
	AcGeCircArc2d arc(p1, p2, dBulge, Adesk::kFalse);

	AcGeLine2d line;
	arc.tangent(p1, line);

	// Draw the arc
	AcGePoint3d P1(p1.x, p1.y, 0.0);
	AcGePoint3d P2(p2.x, p2.y, 0.0);
	AcGePoint2d c(arc.center());
	AcGePoint3d Center(c.x, c.y, 0.0);
	AcGeVector2d refvec(arc.refVec());	// <-- 
	double refAng = refvec.angle();		// <-- This is important!

	AcDbArc *pArc = new AcDbArc(
		Center,
		arc.radius(),
		refAng + arc.startAng(), // <--
		refAng + arc.endAng()	 // <--
	);
	Acad::ErrorStatus postToDb(AcDbEntity* pEnt);
	pArc->setDatabaseDefaults();
	postToDb(pArc);

	// Draw the tangent line
	AcGePoint2d  pl = line.pointOnLine();
	AcGeVector2d dir = line.direction();
	AcGePoint3d pl1(pl.x, pl.y, 0.0);
	AcGeVector3d Dir(dir.x, dir.y, 0.0);

	AcDbLine *pTangentLine = new AcDbLine(pl1, pl1+Dir);
	pTangentLine->setDatabaseDefaults();
	pTangentLine->setColorIndex(1); // red
	postToDb(pTangentLine);


	// Draw a connection line between start- and endpoint
	AcDbLine *pStartToEndPtLine = new AcDbLine(P1, P2);
	pStartToEndPtLine->setDatabaseDefaults();
	pStartToEndPtLine->setColorIndex(3); // green
	postToDb(pStartToEndPtLine);
}

Acad::ErrorStatus postToDb(AcDbEntity* pEnt)
{
	Acad::ErrorStatus      es, es2;
	AcDbBlockTable*        pBlockTable = 0;
	AcDbBlockTableRecord*  pSpaceRecord = 0;

	if (!pEnt)
		return Acad::eNullEntityPointer;

	AcDbDatabase *pDb = acdbHostApplicationServices()->workingDatabase();
	if ((es = pDb->getBlockTable(pBlockTable, AcDb::kForRead)) != Acad::eOk)
		return es;

	if ((es = pBlockTable->getAt(ACDB_MODEL_SPACE, pSpaceRecord, AcDb::kForWrite)) == Acad::eOk)
	{
		AcDbObjectId objId;
		es = pSpaceRecord->appendAcDbEntity(objId, pEnt);
		es2 = pSpaceRecord->close();

		if (es == Acad::eOk)
		{
			es2 = pEnt->downgradeOpen();
			es2 = pEnt->draw();
			pEnt->close();
		}
	}
	es2 = pBlockTable->close();

	return es;
}

Re: AcGeCircArc2d problem with tangent function

mconficconi — Tue, 09 Feb 2016 11:23:13 GMT

I've added the tangent on p2; if the arc is drawed from p1 to p2, why tangent are in the p2-p1 direction?

This was the original question, not how to draw an arc from an AcGeCircArc2dentity...

Sorry for my english;

Best regards

Massimo Conficconi

Re: AcGeCircArc2d problem with tangent function

tbrammer — Tue, 09 Feb 2016 13:16:43 GMT

Yep. Sorry. I should read questions more carefull .

The docs don't say anything about the tangent's direction. I agree with you - I would expect the other direction.

Maybe you should use this base class method instead of tangent():

AcGePoint2d AcGeCurve2d::evalPoint(double,int,AcGeVector2dArray&) const;

Like this:

    AcGeVector2d dir2;
    double param = 0.0;

    if (arc.isOn(p1))
        param = arc.paramOf(p1);
    else
    {
        AcGePointOnCurve2d pntOnCrv;
        arc.getClosestPointTo(p1, pntOnCrv);
        param = pntOnCrv.parameter();
    }

    AcGeVector2dArray derivArray;
    arc.evalPoint(param, 1, derivArray);
    dir2 = derivArray[0];
    dir2.normalize();

dir2 should be guaranteed to point in the right direction.

Re: AcGeCircArc2d problem with tangent function

mconficconi — Tue, 09 Feb 2016 13:29:50 GMT

i'm already test the direction of the curve with the direction formed by center, point, point+direction; different direction imply the negate vector is needed...

Re: AcGeCircArc2d problem with tangent function

tbrammer — Tue, 09 Feb 2016 13:36:19 GMT

The solution I presented above has the advantage to work for every AcGeCurve2d-derived object. So you don't need any class specific code to fix the direction. Use whatever makes you happy