transformBy?No action

[463017170]

static void msddMyGroupMyCommand () {
	ads_name ent;
	ads_point pt;
	AcDbObjectId id0;
	acedEntSel(_T("\nSelect Object"), ent, pt);
	acdbGetObjectId(id0, ent);

	AcGePoint3d startPoint;
	AcGeVector3d  XDir, YDir, ZDir;

	startPoint.set(1000, 1000, 0);

	XDir.set(0.7071  , 0.4082 ,  -0.5774 );
    YDir.set(-0.7071 , 0.4082 ,  -0.5774 );
    ZDir.set(0,         0.8165,   0.5774 );

	AcGeMatrix3d xform;

	xform.setCoordSystem(startPoint, XDir,YDir,ZDir);

	AcDbEntity *pEnt;
	Acad::ErrorStatus es = acdbOpenObject(pEnt, id0, AcDb::kForWrite,false);
	pEnt->transformBy(xform);
	pEnt->close();
}

[tbrammer · Accepted solution]

You should look at the return value of

es = pEnt->transformBy(xform);

Your xform is not a pure rotation matrix. It also contains scaling with different factors.
The scale factors are the lenghts of the vectors XDir, YDir and ZDir. 

They are 0.912822 for XDir and YDir but  1.15471 for ZDir.

Most entities don't support scaling with different scale factors.

Also the vectors are not exactly perpendicular to each other. Calculating the dotproducts yield:

XDir * YDir = 2.759 e-5
YDir * ZDir = XDir * ZDir  = -9.546 e-5