points_at_distance.go

func pointsAtDistance(a, b, c s5t.Point, d float64) (s5t.Point, s5t.Point) {
  // Slope of A-B
	slope := (b.Y - a.Y) / (b.X - a.X)

	// Slope of line perpendicular to A-B
	perpSlope := -1 / slope

	// X components of intersection of circle with radius d with line perpendicular to A-B through C
	xd := d / math.Sqrt(1+math.Pow(perpSlope, 2.0))
	newX1 := c.X + xd
	newX2 := c.X - xd
	newY1 := c.Y - perpSlope*(c.X-newX1)
	newY2 := c.Y - perpSlope*(c.X-newX2)

	return s5t.Point{X: newX1, Y: newY1}, s5t.Point{X: newX2, Y: newY2}
}