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/* joint[0], joint[1] and joint[3] are in degrees and joint[2] is in length units */
static
int scaraKinematicsForward(const double * joint,
                      EmcPose * world,
                      const KINEMATICS_FORWARD_FLAGS * fflags,
                      KINEMATICS_INVERSE_FLAGS * iflags)
{
    double a0, a1, a3;
    double x, y, z, c;

/* convert joint angles to radians for sin() and cos() */

    a0 = joint[0] * ( PM_PI / 180 );
    a1 = joint[1] * ( PM_PI / 180 );
    a3 = joint[3] * ( PM_PI / 180 );
/* convert angles into world coords */

    a1 = a1 + a0;
    a3 = a3 + a1;

    x = D2*cos(a0) + D4*cos(a1) + D6*cos(a3);
    y = D2*sin(a0) + D4*sin(a1) + D6*sin(a3);
    z = D1 + D3 - joint[2] - D5;
    c = a3;

    *iflags = 0;
    if (joint[1] < 90)
        *iflags = 1;

    world->tran.x = x;
    world->tran.y = y;
    world->tran.z = z;
    world->c = c * 180 / PM_PI;

    world->a = joint[4];
    world->b = joint[5];

    return (0);
} //scaraKinematicsForward()

static int scaraKinematicsInverse(const EmcPose * world,
                                  double * joint,
                                  const KINEMATICS_INVERSE_FLAGS * iflags,
                                  KINEMATICS_FORWARD_FLAGS * fflags)
{
    double a3;
    double q0, q1;
    double xt, yt, rsq, cc;
    double x, y, z, c;

    x = world->tran.x;
    y = world->tran.y;
    z = world->tran.z;
    c = world->c;

    /* convert degrees to radians */
    a3 = c * ( PM_PI / 180 );

    /* center of end effector (correct for D6) */
    xt = x - D6*cos(a3);
    yt = y - D6*sin(a3);

    /* horizontal distance (squared) from end effector centerline
        to main column centerline */
    rsq = xt*xt + yt*yt;
    /* joint 1 angle needed to make arm length match sqrt(rsq) */
    cc = (rsq - D2*D2 - D4*D4) / (2*D2*D4);
    if(cc < -1) cc = -1;
    if(cc > 1) cc = 1;
    q1 = acos(cc);

    if (*iflags)
        q1 = -q1;

    /* angle to end effector */
    q0 = atan2(yt, xt);

    /* end effector coords in inner arm coord system */
    xt = D2 + D4*cos(q1);
    yt = D4*sin(q1);

    /* inner arm angle */
    q0 = q0 - atan2(yt, xt);

    /* q0 and q1 are still in radians. convert them to degrees */
    q0 = q0 * (180 / PM_PI);
    q1 = q1 * (180 / PM_PI);

    joint[0] = q0;
    joint[1] = q1;
    joint[2] = D1 + D3 - D5 - z;
    joint[3] = c - ( q0 + q1);
    joint[4] = world->a;
    joint[5] = world->b;

    *fflags = 0;

    return (0);
} // scaraKinematicsInverse()