I was thinking of some constraints I would be interested in using, something like Angle/Angle ratios, ArcLen/Arclen ratios, or ArcLen/LineLen ratios. Currently I can simulate those constraints by doing some convoluted multi-constraining (Arclength1 = LengthA, LengthA / LengthB ratio, LengthB = ArcLength2 ). But ideally these could be implemented as a single constraint.

I took a look at the code and was wondering the amount of work required to implement these. I prototyped some constraint code in the constrainteq file, but I don't know if I'm on the right track, as I don't have the correct compile environment set up.

case ARCL_ARCL_RATIO: {
EntityBase *arc1 = SK.GetEntity(entityA),
*arc2 = SK.GetEntity(entityB);

// And get the arc1 radius, and the cosine of its angle
EntityBase *ao1 = SK.GetEntity(arc1->point[0]),
*as1 = SK.GetEntity(arc1->point[1]),
*af1 = SK.GetEntity(arc1->point[2]);

ExprVector aos1 = (as1->PointGetExprs()).Minus(ao1->PointGetExprs()),
aof1 = (af1->PointGetExprs()).Minus(ao1->PointGetExprs());
Expr *r1 = aof1.Magnitude();

ExprVector n1 = arc1->Normal()->NormalExprsN();
ExprVector u1 = aos1.WithMagnitude(Expr::From(1.0));
ExprVector v1 = n1.Cross(u1);
// so in our new csys, we start at (1, 0, 0)
Expr *costheta1 = aof1.Dot(u1)->Div(r1);
Expr *sintheta1 = aof1.Dot(v1)->Div(r1);

double thetas1, thetaf1, dtheta1;
arc1->ArcGetAngles(&thetas1, &thetaf1, &dtheta1);
Expr *theta1;
if(dtheta1 < 3*PI/4) {
theta1 = costheta1->ACos();
} else if(dtheta1 < 5*PI/4) {
// As the angle crosses pi, cos theta1 is not invertible;
// so use the sine to stop blowing up
theta1 = Expr::From(PI)->Minus(sintheta1->ASin());
} else {
theta1 = (Expr::From(2*PI))->Minus(costheta1->ACos());
}

// And get the arc2 radius, and the cosine of its angle
EntityBase *ao2 = SK.GetEntity(arc2->point[0]),
*as2 = SK.GetEntity(arc2->point[1]),
*af2 = SK.GetEntity(arc2->point[2]);

ExprVector aos2 = (as2->PointGetExprs()).Minus(ao2->PointGetExprs()),
aof2 = (af2->PointGetExprs()).Minus(ao2->PointGetExprs());
Expr *r2 = aof2.Magnitude();

ExprVector n2 = arc2->Normal()->NormalExprsN();
ExprVector u2 = aos2.WithMagnitude(Expr::From(1.0));
ExprVector v2 = n2.Cross(u2);
// so in our new csys, we start at (1, 0, 0)
Expr *costheta2 = aof2.Dot(u2)->Div(r2);
Expr *sintheta2 = aof2.Dot(v2)->Div(r2);

double thetas2, thetaf2, dtheta2;
arc2->ArcGetAngles(&thetas2, &thetaf2, &dtheta2);
Expr *theta2;
if(dtheta2 < 3*PI/4) {
theta2 = costheta2->ACos();
} else if(dtheta2 < 5*PI/4) {
// As the angle crosses pi, cos theta2 is not invertible;
// so use the sine to stop blowing up
theta2 = Expr::From(PI)->Minus(sintheta2->ASin());
} else {
theta2 = (Expr::From(2*PI))->Minus(costheta2->ACos());
}
// And write the equation; (r1*theta1) / ( r2*theta2) = some ratio
AddEq(l, (r1->Times(theta1))->Div(r2->Times(theta2))->Minus(exA), 0);
break;
}
case ARC_LINE_LENGTH_RATIO: {
EntityBase *line = SK.GetEntity(entityA),
*arc1 = SK.GetEntity(entityB);

Expr *ll = Distance(workplane, line->point[0], line->point[1]);

// And get the arc1 radius, and the cosine of its angle
EntityBase *ao1 = SK.GetEntity(arc1->point[0]),
*as1 = SK.GetEntity(arc1->point[1]),
*af1 = SK.GetEntity(arc1->point[2]);

ExprVector aos1 = (as1->PointGetExprs()).Minus(ao1->PointGetExprs()),
aof1 = (af1->PointGetExprs()).Minus(ao1->PointGetExprs());
Expr *r1 = aof1.Magnitude();

ExprVector n1 = arc1->Normal()->NormalExprsN();
ExprVector u1 = aos1.WithMagnitude(Expr::From(1.0));
ExprVector v1 = n1.Cross(u1);
// so in our new csys, we start at (1, 0, 0)
Expr *costheta1 = aof1.Dot(u1)->Div(r1);
Expr *sintheta1 = aof1.Dot(v1)->Div(r1);

double thetas1, thetaf1, dtheta1;
arc1->ArcGetAngles(&thetas1, &thetaf1, &dtheta1);
Expr *theta1;
if(dtheta1 < 3*PI/4) {
theta1 = costheta1->ACos();
} else if(dtheta1 < 5*PI/4) {
// As the angle crosses pi, cos theta1 is not invertible;
// so use the sine to stop blowing up
theta1 = Expr::From(PI)->Minus(sintheta1->ASin());
} else {
theta1 = (Expr::From(2*PI))->Minus(costheta1->ACos());
}

// And write the equation; (r1*theta1) / ( length) = some ratio
AddEq(l, (r1->Times(theta1))->Div(ll)->Minus(exA), 0);
break;
}