三点画弧

admin1

AcGePoint2d pt1 pt2 pt3;
AcGePoint2d center.

Lets find the center point of the Arc:

double yDeltaA = pt2.y - pt1.y;

double xDeltaA = pt2.x - pt1.x;

double yDeltaB = pt3.y - pt2.y;

double xDeltaB = pt3.x - pt2.x;

//case for vertical or horizontal

if (fabs(xDeltaA) <= fuzz && fabs(yDeltaB) <= fuzz){

center.x = (pt2.x + pt3.x)/2.0;

center.y = (pt1.y + pt2.y)/2.0;

} else {

double aSlope=yDeltaA/xDeltaA;

double bSlope=yDeltaB/xDeltaB;

// checking whether the given points are colinear.

if (fabs(aSlope-bSlope) <= fuzz) return false;

center.x = (aSlope*bSlope*(pt1.y - pt3.y) + bSlope*(pt1.x + pt2.x)

- aSlope*(pt2.x+pt3.x))/(2* (bSlope-aSlope));

center.y = -1*(center.x - (pt1.x+pt2.x)/2.0)/aSlope+(pt1.y+pt2.y)/2.0;

}

Now to calculate the bulge we need the included angle.
The bulge is calculates as tan(includedAngle/4.0);

So get the Angles:
double startang = acutAngle(asPtn2d(center), asPtn2d(pt1));

double endang = acutAngle(asPtn2d(center), asPtn2d(pt3));

We now need to know the clock but there are 2 posibilities!
Your function is fine here but change it to accept to a AcGePoint2d

clock1 = cwisept (pt1, pt2, pt3);
clock2 = cwisept (pt1, center, pt3);

The diff_angle function normalises the angle
if (clock1 == clock2) {

includedAngle = 2.0*_PI-diff_angle(startang, endang);

} else {

includedAngle = diff_angle(endang, startang);

}

double bulge = tan(includedAngle/4.0);

That it!

So to make it!
AcDbPolyline *plx = new AcDbPolyline;

plx->addVertexAt(0, pt1, bulge);

plx->addVertexAt(1, pt3, 0.0);

now Append the entity to the database and you are done!



Regards Gary.

[url]www.drcauto.com[/url]

#define ANG360 (2.0*_PI)

double diff_angle(double a1x, double a2x )

{

double delta;

double a1, a2;

a1 = fmod(a1x, ANG360);

a2 = fmod(a2x, ANG360);

if(fabs(a1) > _PI ) {

if( a1 < 0.0 )

a1 += ANG360;

else

a1 -= ANG360;

}

if (fabs(a2) > _PI) {

if( a2 < 0.0 )

a2 += ANG360;

else

a2 -= ANG360;

}

delta = a1 - a2;

if(delta > ANG360) {

delta = fmod(delta, ANG360);

}

if(fabs(delta) > _PI) {

if(delta < 0.0 )

delta += ANG360;

else

delta -= ANG360;

}

return delta;

}