diff --git a/large_image/__init__.py b/large_image/__init__.py
index e29b8885e..d92fa01f7 100644
--- a/large_image/__init__.py
+++ b/large_image/__init__.py
@@ -20,7 +20,8 @@
 import server
 from server import tilesource
 from server import cache_util
+from server import util
 
 getTileSource = tilesource.getTileSource  # noqa
 
-__all__ = ['server', 'tilesource', 'getTileSource', 'cache_util']
+__all__ = ['server', 'tilesource', 'getTileSource', 'cache_util', 'util']
diff --git a/plugin.cmake b/plugin.cmake
index b15bd9929..fcef0b9d7 100644
--- a/plugin.cmake
+++ b/plugin.cmake
@@ -107,6 +107,8 @@ add_python_test(girderless PLUGIN large_image
 set_property(TEST server_large_image.girderless APPEND PROPERTY ENVIRONMENT
   "LARGE_IMAGE_DATA=${PROJECT_BINARY_DIR}/data/plugins/large_image")
 
+add_python_test(util PLUGIN large_image)
+
 add_python_test(examples PLUGIN large_image
   # There is a bug in cmake that fails when external data files are added to
   # multiple tests, so comment out the external data directive.
diff --git a/plugin_tests/util_test.py b/plugin_tests/util_test.py
new file mode 100644
index 000000000..19b6af821
--- /dev/null
+++ b/plugin_tests/util_test.py
@@ -0,0 +1,69 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+import unittest
+
+
+class LargeImageUtilTest(unittest.TestCase):
+    def testUncrossPolygon(self):
+        from large_image import util
+
+        testPairs = [(  # (input, output)
+            # Do nothing if the polygon doesn't cross
+            [[0, 0], [0, 2], [2, 2], [2, 0]],
+            [[0, 0], [0, 2], [2, 2], [2, 0]],
+        ), (
+            # Always covner polygons to clockwise
+            [[0, 0], [2, 0], [2, 2], [0, 2]],
+            [[0, 0], [0, 2], [2, 2], [2, 0]],
+        ), (
+            # Uncross a polygon
+            [[0, 4], [0, 2], [2, 2], [2, 0], [0, 0], [2, 4]],
+            [[0, 4], [2, 4], [1, 2], [2, 2], [2, 0], [0, 0], [1, 2], [0, 2]]
+        ), (
+            # Discard degenerate polygons
+            [[0, 4]],
+            [],
+        ), (
+            # Discard degenerate polygons
+            [],
+            [],
+        ), (
+            # Discard degenerate polygons, even if they have valid holes
+            [[[0, 4]],
+             [[1, 1], [1, 3], [3, 3], [3, 1]]],
+            [[]],
+        ), (
+            # Merge a hole with a polygon if the hole crosses it
+            [[[0, 0], [0, 2], [2, 2], [2, 0]],
+             [[1, 1], [1, 3], [3, 3], [3, 1]]],
+            [[[0, 0], [0, 2], [1, 2], [1, 1], [2, 1], [2, 2], [1, 2], [1, 3],
+              [3, 3], [3, 1], [2, 1], [2, 0]]],
+        ), (
+            # Keep non-crossing holes, but holes are counter-clockwise
+            [[[0, 0], [0, 4], [4, 4], [4, 0]],
+             [[1, 1], [1, 3], [3, 3], [3, 1]]],
+            [[[0, 0], [0, 4], [4, 4], [4, 0]],
+             [[3, 1], [3, 3], [1, 3], [1, 1]]]
+        ), (
+            # Discard degenerate holes
+            [[[0, 0], [0, 4], [4, 4], [4, 0]],
+             [[1, 1], [1, 1], [1, 1], [1, 1]]],
+            [[[0, 0], [0, 4], [4, 4], [4, 0]]]
+        ), (
+            # Handle coincident lines
+            [[0, 0], [0, 2], [0, 1], [0, 3], [3, 3], [3, 0]],
+            [[0, 0], [0, 2], [0, 1], [0, 2], [0, 3], [3, 3], [3, 0]]
+        ), (
+            # Handle coincident lines with a different ordering
+            [[0, 0], [0, 3], [0, 1], [0, 2], [3, 2], [3, 0]],
+            [[0, 0], [0, 1], [0, 2], [0, 1], [0, 2], [0, 3], [0, 2], [3, 2], [3, 0]]
+        ), (
+            # Handle coincident lines with holes
+            [[0, 0], [3, 0], [3, 1], [1, 1], [1, 0], [2, 0], [2, 2], [0, 2]],
+            [[0, 0], [0, 2], [2, 2], [2, 1], [3, 1], [3, 0], [2, 0], [1, 0],
+             [2, 0], [2, 1], [1, 1], [1, 0]]
+        )]
+
+        for input, output in testPairs:
+            self.assertEqual(util.uncrossPolygon(input), output)
diff --git a/server/__init__.py b/server/__init__.py
index d1a801c34..ed39c4349 100644
--- a/server/__init__.py
+++ b/server/__init__.py
@@ -34,3 +34,4 @@
     # if girder is available, and we fail to import anything else, girder will
     # show the failure
     from .base import load  # noqa
+from . import util  # noqa
diff --git a/server/util/__init__.py b/server/util/__init__.py
new file mode 100644
index 000000000..aa3c55c8a
--- /dev/null
+++ b/server/util/__init__.py
@@ -0,0 +1,262 @@
+# General utility functions
+
+from six.moves import range
+
+
+def distance2dSquared(pt1, pt2):
+    """
+    Get the square of the Euclidean 2D distance between two points.
+
+    :param pt1: The first point.  This is an array with at least two numeric
+        elements.
+    :param pt2: The second point.
+    :returns: The distance squared.
+    """
+    dx = pt1[0] - pt2[0]
+    dy = pt1[1] - pt2[1]
+    return dx * dx + dy * dy
+
+
+def distance2dToLineSquared(pt, line1, line2):
+    """
+    Get the square of the Euclidean 2D distance between a point and a line
+    segment.
+
+    :param pt: The point.
+    :param line1: One end of the line.
+    :param line2: The other end of the line.
+    :returns: The distance squared.
+    """
+    dx = line2[0] - line1[0]
+    dy = line2[1] - line1[1]
+    lengthSquared = dx * dx + dy * dy
+    t = 0
+    if lengthSquared:
+        t = float((pt[0] - line1[0]) * dx + (pt[1] - line1[1]) * dy) / lengthSquared
+        t = max(0, min(1, t))
+    return distance2dSquared(pt, [line1[0] + t * dx, line1[1] + t * dy])
+
+
+def triangleTwiceSignedArea2d(pt1, pt2, pt3):
+    """
+    Get twice the signed area of a 2d triangle.
+
+    :param pt1: A vertex.  This is an array with at least two numeric elements.
+    :param pt2: A vertex.
+    :param pt3: A vertex.
+    :returns: Twice the signed area.
+    """
+    return (pt2[1] - pt1[1]) * (pt3[0] - pt2[0]) - (pt2[0] - pt1[0]) * (pt3[1] - pt2[1])
+
+
+def crossLineSegments2d(seg1pt1, seg1pt2, seg2pt1, seg2pt2):
+    """
+    Determine if two line segments cross.  They are not considered crossing if
+    they share a vertex.  They are crossing if either of one segment's
+    vertices are colinear with the other segment.
+
+    :param line1pt1: one endpoint on the first segment.
+    :param line1pt2: the other endpoint on the first segment.
+    :param line2pt1: one endpoint on the second segment.
+    :param line2pt2: the other endpoint on the second segment.
+    :returns: True uf the segments cross.
+    """
+    # If the segments don't have any overlap in x or y, they can't cross
+    if ((seg1pt1[0] > seg2pt1[0] and seg1pt1[0] > seg2pt2[0] and
+         seg1pt2[0] > seg2pt1[0] and seg1pt2[0] > seg2pt2[0]) or
+        (seg1pt1[0] < seg2pt1[0] and seg1pt1[0] < seg2pt2[0] and
+         seg1pt2[0] < seg2pt1[0] and seg1pt2[0] < seg2pt2[0]) or
+        (seg1pt1[1] > seg2pt1[1] and seg1pt1[1] > seg2pt2[1] and
+         seg1pt2[1] > seg2pt1[1] and seg1pt2[1] > seg2pt2[1]) or
+        (seg1pt1[1] < seg2pt1[1] and seg1pt1[1] < seg2pt2[1] and
+         seg1pt2[1] < seg2pt1[1] and seg1pt2[1] < seg2pt2[1])):
+        return False
+    # If any vertex is in common, it is not considered crossing
+    if (seg1pt1 == seg2pt1 or seg1pt1 == seg2pt2 or seg1pt2 == seg2pt1 or
+            seg1pt2 == seg2pt2):
+        return False
+    # If the lines cross, the signed area of the triangles formed between one
+    # segment and the other's vertices will have different signs.  By using
+    # > 0, colinear points are crossing.
+    if (triangleTwiceSignedArea2d(seg1pt1, seg1pt2, seg2pt1) *
+            triangleTwiceSignedArea2d(seg1pt1, seg1pt2, seg2pt2) > 0 or
+            triangleTwiceSignedArea2d(seg2pt1, seg2pt2, seg1pt1) *
+            triangleTwiceSignedArea2d(seg2pt1, seg2pt2, seg1pt2) > 0):
+        return False
+    return True
+
+
+def lineIntersection2d(line1pt1, line1pt2, line2pt1, line2pt2):
+    """
+    Given lines defined by pairs of points, find the point of intersection.
+
+    :param line1pt1: a point on the first line.
+    :param line1pt2: a second point on the first line.
+    :param line2pt1: a point on the second line.
+    :param line2pt2: a second point on the second line.
+    :returns: the point of intersection, or None if the lines are parallel.
+    """
+    line1dx, line1dy = line1pt1[0] - line1pt2[0], line1pt1[1] - line1pt2[1]
+    line2dx, line2dy = line2pt1[0] - line2pt2[0], line2pt1[1] - line2pt2[1]
+    det = float(line1dx * line2dy - line1dy * line2dx)
+    if not det:
+        return
+    return [
+        ((line1pt1[0] * line1pt2[1] - line1pt1[1] * line1pt2[0]) * line2dx -
+         (line2pt1[0] * line2pt2[1] - line2pt1[1] * line2pt2[0]) * line1dx) / det,
+        ((line1pt1[0] * line1pt2[1] - line1pt1[1] * line1pt2[0]) * line2dy -
+         (line2pt1[0] * line2pt2[1] - line2pt1[1] * line2pt2[0]) * line1dy) / det,
+    ]
+
+
+def lineIntersectionOrEndpoint(line1pt1, line1pt2, line2pt1, line2pt2):
+    """
+    Given lines defined by pairs of points, find the point of intersection.  If
+    the two lines are coincident, return a endpoint that is not in common.
+
+    :param line1pt1: a point on the first line.
+    :param line1pt2: a second point on the first line.
+    :param line2pt1: a point on the second line.
+    :param line2pt2: a second point on the second line.
+    :returns: the point of intersection, or None if the lines are parallel and
+        do not overlap.
+    """
+    crossPt = lineIntersection2d(line1pt1, line1pt2, line2pt1, line2pt2)
+    if crossPt:
+        return crossPt
+    for pt in (line1pt1, line1pt2):
+        if pt != line2pt1 and pt != line2pt2:
+            if not distance2dToLineSquared(pt, line2pt1, line2pt2):
+                return pt
+    for pt in (line2pt1, line2pt2):
+        if pt != line1pt1 and pt != line1pt2:
+            if not distance2dToLineSquared(pt, line1pt1, line1pt2):
+                return pt
+    # The two lines segments do not overlap
+
+
+def uncrossPolygonWithoutHoles(vertices):
+    """
+    Given a list of vertices ensure that the polygon does not cross itself.
+    Repeated vertices are removed.  If resulting polygon has 2 or less vertices
+    (this can only happen if so specified or there are duplicate vertices), an
+    empty list is returned.
+
+    :param vertices: a list of vertices of the polygon.  Each vertex is a list
+        of at least 2 coordinates (only the first two values are considered).
+    :returns: vertices: a list of vertices.
+    """
+    if len(vertices) <= 2:
+        return []
+    # Add the first point at the end so we can skip some modulo work
+    pts = vertices[:] + vertices[0:1]
+    idx1 = 0
+    # Iterate through all segments but the last
+    while idx1 < len(pts) - 2:
+        seg1pt1 = pts[idx1]
+        seg1pt2 = pts[idx1 + 1]
+        idx2 = idx1 + 1
+        # Iterate through the remaining segments
+        while idx2 < len(pts) - 1:  # - 1 sicne we duplicated the first point
+            seg2pt1 = pts[idx2]
+            seg2pt2 = pts[idx2 + 1]
+            # Check if the two segments cross
+            if crossLineSegments2d(seg1pt1, seg1pt2, seg2pt1, seg2pt2):
+                # If crossing, add the crossing point and reverse the loop
+                crossPt = lineIntersectionOrEndpoint(seg1pt1, seg1pt2, seg2pt1, seg2pt2)
+                pts = (pts[:idx1 + 1] + [crossPt] + pts[idx2:idx1:-1] +
+                       [crossPt] + pts[idx2 + 1:])
+                break
+            idx2 += 1
+        else:
+            idx1 += 1
+    # Get rid of duplicates except the duplicated first point
+    pts = [pt for idx, pt in enumerate(pts) if not idx or pt != pts[idx - 1]]
+    # Ensure clockwiseness (if counterclockwise, reverse points).
+    #   This still leaves the possibility that the original polygon contained
+    # two separable loops that are in different orientations.  For instance, if
+    # the polygon is two triangles that share a single vertex and no edges, the
+    # two triangles would ideally be in opposite orientations if one is inside
+    # the other and the same orientation if they are not.  Adjusting this is
+    # currently beyond the scope of this function.
+    if sum((pts[idx + 1][0] - pt[0]) * (pts[idx + 1][1] + pt[1])
+           for idx, pt in enumerate(pts[:-1])) < 0:
+        pts = pts[::-1]
+    # Remove duplicated first point
+    pts = pts[:-1]
+    return pts
+
+
+def mergeCrossingPolygons(poly1, poly2):
+    """
+    Given two polygons, check if any edge from the first polygon crosses any
+    edge in the second polygon.  If so, merge the two polygons by adding the
+    crossing point, combining the second polygon at this point, and passing the
+    result through `uncrossPolygonWithoutHoles`.
+
+    :param poly1: a list of vertices forming an uncrossed polygon without
+        holes.
+    :param poly2: a list of vertices forming an uncrossed polygon without
+        holes.
+    :returns: None if the polygons do not cross, or a new polygon if they do.
+    """
+    for idx1, seg1pt1 in enumerate(poly1):
+        seg1pt2 = poly1[(idx1 + 1) % len(poly1)]
+        for idx2, seg2pt1 in enumerate(poly2):
+            seg2pt2 = poly2[(idx2 + 1) % len(poly2)]
+            if crossLineSegments2d(seg1pt1, seg1pt2, seg2pt1, seg2pt2):
+                # If crossing, combine the polygons at the crossing point
+                crossPt = lineIntersectionOrEndpoint(seg1pt1, seg1pt2, seg2pt1, seg2pt2)
+                poly = (poly1[:idx1 + 1] + [crossPt] +
+                        (poly2[idx2 + 1:] + poly2[:idx2 + 1])[::-1] +
+                        [crossPt] + poly1[idx1 + 1:])
+                return uncrossPolygonWithoutHoles(poly)
+
+
+def uncrossPolygon(vertices):
+    """
+    Given a list of vertices, or a list of lists of vertices where the first
+    entry if the polygon and subsequent entries are holes, ensure that the
+    polygon does not cross itself.  Each hole is uncrossed on its own.  If two
+    holes (or a hole and a polygon) cross each other, they are
+    joined into a single more complicated polygon.  Repeated vertices and
+    degenerate polygons (2 or less vertices) are removed.
+
+    :param vertices: a list of vertices of the polygon.  Each vertex is a list
+        of at least 2 coordinates (only the first two values are considered).
+        Alternately, a list of lists of vertices, where the first entry is the
+        polygon and subsequent entries are holes.
+    :returns: vertices: a list of vertices or a list of lists of vertices.
+        This has the same depth as the original argument.
+    """
+    if not len(vertices) or not len(vertices[0]):
+        return vertices
+    if not isinstance(vertices[0][0], list):
+        return uncrossPolygonWithoutHoles(vertices)
+    # uncross the outer polygon and all holes
+    polygons = [uncrossPolygonWithoutHoles(pts) for pts in vertices]
+    # If the containing polygon is degenerate, return an empty set
+    if not len(polygons[0]):
+        return [[]]
+    # discard degenerate holes
+    polygons = [polygon for polygon in polygons if len(polygon)]
+    # For each polygon, check if it crosses any other polygon.  If it does,
+    # join them together at the first crossing point and uncross the result.
+    pidx1 = 0
+    while pidx1 < len(polygons) - 1:
+        poly1 = polygons[pidx1]
+        pidx2 = pidx1 + 1
+        while pidx2 < len(polygons):
+            poly2 = polygons[pidx2]
+            crossed = mergeCrossingPolygons(poly1, poly2)
+            if crossed:
+                polygons[pidx1] = crossed
+                del polygons[pidx2]
+                break
+            pidx2 += 1
+        else:
+            pidx1 += 1
+    # reverse all holes so that they are opposite direction as the main polygon
+    for idx in range(1, len(polygons)):
+        polygons[idx] = polygons[idx][::-1]
+    return polygons