lw_dist2d_circle_intersections()

static int lw_dist2d_circle_intersections ( const POINT2D *  A1, const POINT2D *  A2, const POINT2D *  A3, const POINT2D *  center_A, double  radius_A, const POINT2D *  P, POINT2D *  I, uint32_t *  ni  )

static

Calculates the intersection points of a circle and line.

This function assumes the center and test point are distinct. Finds the line between the circle center and test point, and the two intersection points on the circle defined by that line. If those points fall within the provided arc (A1,A2,A3) then the points are added to the provided array (I) and the array length counter is incremented.

Parameters

A1	Point of arc
A2	Point of arc
A3	Point of arc
center_A	Center of arc A circle
radius_A	Radius of arc A circle
P	Point to use in calculating intersection line
I	[out] Pointer to an return value array
ni	[out] Pointer to return array size counter

Returns

int

Definition at line 1577 of file measures.c.

{
        POINT2D R;
 
        // If the test point is on the center of the other
        // arc, some other point has to be closer, by definition.
        if (p2d_same(center_A, P))
                return 0;
 
        // Calculate vector from the center to the pt
        double dir_x = center_A->x - P->x;
        double dir_y = center_A->y - P->y;
        double dist = sqrt(dir_x * dir_x + dir_y * dir_y);
 
        // Normalize the direction vector to get a unit vector (length = 1)
        double unit_x = dir_x / dist;
        double unit_y = dir_y / dist;
 
        // Calculate the two intersection points on the circle
        // Point 1: Move from center_A along the unit vector by distance radius_A
        R.x = center_A->x + unit_x * radius_A;
        R.y = center_A->y + unit_y * radius_A;
        if (lw_pt_in_arc(&R, A1, A2, A3))
                I[(*ni)++] = R;
 
        // Point 2: Move from center_A against the unit vector by distance radius_A
        R.x = center_A->x - unit_x * radius_A;
        R.y = center_A->y - unit_y * radius_A;
        if (lw_pt_in_arc(&R, A1, A2, A3))
                I[(*ni)++] = R;
 
        return 0;
}

References lw_pt_in_arc(), p2d_same(), POINT2D::x, and POINT2D::y.

Referenced by lw_dist2d_arc_arc().

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