From 164cb51dc5bc4debc6a95a54f213f6dc20994b99 Mon Sep 17 00:00:00 2001
From: snowman2 <alansnow21@gmail.com>
Date: Thu, 7 Jan 2021 18:50:45 -0600
Subject: [PATCH] BUG: Allow transformations with empty arrays

---
 docs/history.rst         |  1 +
 pyproj/_transformer.pyx  |  4 ++--
 test/test_transformer.py | 19 ++++++++++++++++++-
 3 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/docs/history.rst b/docs/history.rst
index a2173c280..bc17c6e80 100644
--- a/docs/history.rst
+++ b/docs/history.rst
@@ -4,6 +4,7 @@ Change Log
 3.0.1
 -----
 * Use `proj_context_errno_string` in PROJ 8+ due to deprecation (issue #760)
+* BUG: Allow transformations with empty arrays (issue #766)
 
 3.0.0
 -----
diff --git a/pyproj/_transformer.pyx b/pyproj/_transformer.pyx
index 339fadb49..6a80bb794 100644
--- a/pyproj/_transformer.pyx
+++ b/pyproj/_transformer.pyx
@@ -481,8 +481,8 @@ cdef class _Transformer(Base):
             buflent = xbuff.len
             tt = NULL
 
-        if not xbuff.len or not (xbuff.len == ybuff.len == buflenz == buflent):
-            raise ProjError('x, y, z, and time must be same size')
+        if not (xbuff.len == ybuff.len == buflenz == buflent):
+            raise ProjError('x, y, z, and time must be same size if included.')
 
         cdef Py_ssize_t iii
         cdef int errno = 0
diff --git a/test/test_transformer.py b/test/test_transformer.py
index 06504533c..eb1b943ec 100644
--- a/test/test_transformer.py
+++ b/test/test_transformer.py
@@ -7,7 +7,7 @@
 
 import numpy as np
 import pytest
-from numpy.testing import assert_almost_equal
+from numpy.testing import assert_almost_equal, assert_array_equal
 
 import pyproj
 from pyproj import Proj, Transformer, itransform, transform
@@ -402,6 +402,23 @@ def test_always_xy__itransform():
         )
 
 
+@pytest.mark.parametrize("empty_array", [(), [], np.array([])])
+def test_transform_empty_array_xy(empty_array):
+    transformer = Transformer.from_crs(2193, 4326)
+    assert_array_equal(
+        transformer.transform(empty_array, empty_array), (empty_array, empty_array)
+    )
+
+
+@pytest.mark.parametrize("empty_array", [(), [], np.array([])])
+def test_transform_empty_array_xyzt(empty_array):
+    transformer = Transformer.from_pipeline("+init=ITRF2008:ITRF2000")
+    assert_array_equal(
+        transformer.transform(empty_array, empty_array, empty_array, empty_array),
+        (empty_array, empty_array, empty_array, empty_array),
+    )
+
+
 def test_transform_direction__string():
     forward_transformer = Transformer.from_crs(4326, 3857)
     inverse_transformer = Transformer.from_crs(3857, 4326)