From 277233bd1a589feeb648947256e34b0b4fb6f540 Mon Sep 17 00:00:00 2001
From: Thomas Robitaille <thomas.robitaille@gmail.com>
Date: Tue, 24 May 2016 11:27:56 +0100
Subject: [PATCH] Fix a bug that caused WCSAxes to crash when trying to
 transform arrays with zero coordinates.

---
 CHANGES.md            |  3 +++
 wcsaxes/transforms.py | 10 ++++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/CHANGES.md b/CHANGES.md
index a02b228..1fcd307 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -3,6 +3,9 @@
 
 - Added property getters for color and linewidth in BaseFrame. [#203]
 
+- Fix a bug that caused WCSAxes to crash when trying to transform arrays with
+  zero coordinates. [#202]
+
 0.7 (2016-05-06)
 ----------------
 
diff --git a/wcsaxes/transforms.py b/wcsaxes/transforms.py
index 44d2b76..bc6401a 100644
--- a/wcsaxes/transforms.py
+++ b/wcsaxes/transforms.py
@@ -95,7 +95,10 @@ def transform(self, world):
         if world.shape[1] != self.wcs.wcs.naxis:
             raise ValueError("Second dimension of input values should match number of WCS coordinates")
 
-        pixel = self.wcs.wcs_world2pix(world, 1) - 1
+        if world.shape[0] == 0:
+            pixel = np.zeros((0, 2))
+        else:
+            pixel = self.wcs.wcs_world2pix(world, 1) - 1
 
         if self.slice is None:
             return pixel
@@ -162,7 +165,10 @@ def transform(self, pixel):
 
         pixel_full += 1
 
-        world = self.wcs.wcs_pix2world(pixel_full, 1)
+        if pixel_full.shape[0] == 0:
+            world = np.zeros((0, 2))
+        else:
+            world = self.wcs.wcs_pix2world(pixel_full, 1)
 
         # At the moment, one has to manually check that the transformation
         # round-trips, otherwise it should be considered invalid.