allows user to specify polar_angle direction (#37)

TESTS/unitTests.py

@@ -1069,6 +1069,27 @@ def test10(self):
         res = pt.synthetic_images.square_wave(20, frequency=(1,2), amplitude=3.2, phase=-2, origin=(2,3), twidth=.55)
         self.assertTrue(pt.compareRecon(matPyr['res'], res))
 
+class polarAngleTests(unittest.TestCase):
+    def test0(self):
+        ang = pt.synthetic_images.polar_angle(100, direction='clockwise')
+        idx = np.argmin((ang - np.pi/2)**2)
+        # check that pi/2 is in the bottom half of the image
+        self.assertTrue(np.unravel_index(idx, (100, 100))[0] > 50)
+        idx = np.argmin((ang + np.pi/2)**2)
+        # check that -pi/2 is in the top half of the image
+        self.assertTrue(np.unravel_index(idx, (100, 100))[0] < 50)
+    def test1(self):
+        ang = pt.synthetic_images.polar_angle(100, direction='counter-clockwise')
+        idx = np.argmin((ang - np.pi/2)**2)
+        # check that pi/2 is in the top half of the image
+        self.assertTrue(np.unravel_index(idx, (100, 100))[0] < 50)
+        idx = np.argmin((ang + np.pi/2)**2)
+        # check that -pi/2 is in the bottom half of the image
+        self.assertTrue(np.unravel_index(idx, (100, 100))[0] > 50)
+    def test2(self):
+        with self.assertRaises(ValueError):
+            pt.synthetic_images.polar_angle(100, direction='-clockwise')
+
 # TODO
 
 # python version of histo

src/pyrtools/tools/synthetic_images.py

@@ -136,11 +136,12 @@ def polar_radius(size, exponent=1, origin=None):
     return res
 
 
-def polar_angle(size, phase=0, origin=None):
+def polar_angle(size, phase=0, origin=None, direction='clockwise'):
     '''make polar angle matrix (in radians)
 
-    Compute a matrix of given size containing samples of the polar angle (in radians, CW from the
-    X-axis, ranging from -pi to pi), relative to given phase, about the given origin pixel.
+    Compute a matrix of given size containing samples of the polar angle (in radians,
+    increasing in user-defined direction from the X-axis, ranging from -pi to pi), relative to
+    given phase, about the given origin pixel.
 
     Arguments
     ---------
@@ -153,13 +154,20 @@ def polar_angle(size, phase=0, origin=None):
         the center of the image. if an int, we assume the origin is at `(origin, origin)`. if a
         tuple, must be a 2-tuple of ints specifying the origin (where `(0, 0)` is the upper left).
         if None, we assume the origin lies at the center of the matrix, `(size+1)/2`.
+    direction : {'clockwise', 'counter-clockwise'}
+        Whether the angle increases in a clockwise or counter-clockwise direction from
+        the x-axis. The standard mathematical convention is to increase
+        counter-clockwise, so that 90 degrees corresponds to the positive y-axis.
 
     Returns
     -------
     res : `np.array`
         the polar angle matrix
 
     '''
+    if direction not in ['clockwise', 'counter-clockwise']:
+        raise ValueError("direction must be one of {'clockwise', 'counter-clockwise'}, "
+                         f"but received {direction}!")
     if not hasattr(size, '__iter__'):
         size = (size, size)
 
@@ -172,6 +180,8 @@ def polar_angle(size, phase=0, origin=None):
                                np.arange(1, size[0]+1)-origin[0])
     xramp = np.array(xramp)
     yramp = np.array(yramp)
+    if direction == 'counter-clockwise':
+        yramp = np.flip(yramp, 0)
 
     res = np.arctan2(yramp, xramp)