From Ulrich Hertlein, "on my MacOS X/cmake setup the zlib plugin isn't built by default. This may be because zlib.h is

installed in /opt/local/include on my system (courtesy of DarwinPorts).  I've added a CMakeModule to
look for zlib.h and the library in various places.  The files are attached."

CMakeLists.txt

@@ -147,6 +147,7 @@ FIND_PACKAGE(COLLADA)
 FIND_PACKAGE(Xine)
 FIND_PACKAGE(OpenVRML)
 FIND_PACKAGE(Performer)
+FIND_PACKAGE(ZLIB)
 
 # SET(DESIRED_QT_VERSION 3)
 # FIND_PACKAGE(Qt)

CMakeModules/FindZLIB.cmake

@@ -0,0 +1,56 @@
+# Locate gdal
+# This module defines
+# ZLIB_LIBRARY
+# ZLIB_FOUND, if false, do not try to link to gdal 
+# ZLIB_INCLUDE_DIR, where to find the headers
+#
+# $ZLIB_DIR is an environment variable that would
+# correspond to the ./configure --prefix=$ZLIB_DIR
+# used in building gdal.
+#
+# Created by Ulrich Hertlein. 
+
+FIND_PATH(ZLIB_INCLUDE_DIR zlib.h
+    $ENV{ZLIB_DIR}/include
+    $ENV{ZLIB_DIR}
+    $ENV{OSGDIR}/include
+    $ENV{OSGDIR}
+    $ENV{OSG_ROOT}/include
+    ~/Library/Frameworks
+    /Library/Frameworks
+    /usr/local/include
+    /usr/include
+    /sw/include # Fink
+    /opt/local/include # DarwinPorts
+    /opt/csw/include # Blastwave
+    /opt/include
+    [HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\Control\\Session\ Manager\\Environment;OSG_ROOT]/include
+    /usr/freeware/include
+)
+
+FIND_LIBRARY(ZLIB_LIBRARY 
+    NAMES z libz
+    PATHS
+    $ENV{ZLIB_DIR}/lib
+    $ENV{ZLIB_DIR}
+    $ENV{OSGDIR}/lib
+    $ENV{OSGDIR}
+    $ENV{OSG_ROOT}/lib
+    ~/Library/Frameworks
+    /Library/Frameworks
+    /usr/local/lib
+    /usr/lib
+    /sw/lib
+    /opt/local/lib
+    /opt/csw/lib
+    /opt/lib
+    [HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\Control\\Session\ Manager\\Environment;OSG_ROOT]/lib
+    /usr/freeware/lib64
+)
+
+SET(ZLIB_FOUND "NO")
+IF(ZLIB_LIBRARY AND ZLIB_INCLUDE_DIR)
+    SET(ZLIB_FOUND "YES")
+ENDIF(ZLIB_LIBRARY AND ZLIB_INCLUDE_DIR)
+
+