code release

xlib/math/math_.py

@@ -0,0 +1,46 @@
+import numpy as np
+import numpy.linalg as npla
+
+
+def segment_length(p1 : np.ndarray, p2 : np.ndarray):
+    """
+        p1  (2,)
+        p2  (2,)
+    """
+    return npla.norm(p2-p1)
+
+def segment_to_vector(p1 : np.ndarray, p2 : np.ndarray):
+    """
+        p1  (2,)
+        p2  (2,)
+    """
+    x = p2-p1
+    x /= npla.norm(x)
+    return x
+
+
+def intersect_two_line(a1, a2, b1, b2) -> np.ndarray:
+    """
+    Returns the point of intersection of the lines (not segments) passing through a2,a1 and b2,b1.
+    a1: [x, y] a point on the first line
+    a2: [x, y] another point on the first line
+    b1: [x, y] a point on the second line
+    b2: [x, y] another point on the second line
+    """
+    s = np.vstack([a1,a2,b1,b2])        # s for stacked
+    h = np.hstack((s, np.ones((4, 1)))) # h for homogeneous
+    l1 = np.cross(h[0], h[1])           # get first line
+    l2 = np.cross(h[2], h[3])           # get second line
+    x, y, z = np.cross(l1, l2)          # point of intersection
+    if z == 0:                          # lines are parallel
+        return (float('inf'), float('inf'))
+    return np.array( [x/z, y/z], np.float32 )
+
+def polygon_area(poly : np.ndarray) -> float:
+    """
+    calculate area of n-vertices polygon with non intersecting edges
+
+        poly   np.ndarray (n,2)
+    """
+    return float( np.abs(np.sum( poly[:,0] * np.roll( poly[:,1], -1  ) - poly[:,1] * np.roll( poly[:,0], -1  )  ) / 2) )
+