From 983919404f90fdc489f9adfef10d9b04e95bd3b4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Johannes=20Sch=C3=B6nberger?= <jsch@demuc.de>
Date: Wed, 24 Dec 2014 15:24:34 +0100
Subject: [PATCH] Improve conditioning of homography design matrix

---
 skimage/transform/_geometric.py | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/skimage/transform/_geometric.py b/skimage/transform/_geometric.py
index cd9d9487..ca8f6329 100644
--- a/skimage/transform/_geometric.py
+++ b/skimage/transform/_geometric.py
@@ -264,6 +264,10 @@ class ProjectiveTransform(GeometricTransform):
             Destination coordinates.
 
         """
+
+        src_matrix, src = _center_and_normalize_points(src)
+        dst_matrix, dst = _center_and_normalize_points(dst)
+
         xs = src[:, 0]
         ys = src[:, 1]
         xd = dst[:, 0]
@@ -296,6 +300,9 @@ class ProjectiveTransform(GeometricTransform):
         H.flat[list(self._coeffs) + [8]] = - V[-1, :-1] / V[-1, -1]
         H[2, 2] = 1
 
+        # De-center and de-normalize
+        H = np.dot(np.linalg.inv(dst_matrix), np.dot(H, src_matrix))
+
         self.params = H
 
     def __add__(self, other):