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+# Proj bridge to Java
+
+This is the third release of JNI wrappers for the main Proj functions.
+The first release of JNI wrappers were created by http://www.hydrologis.com.
+The second release of JNI wrappers were created by http://www.geoapi.org.
+
+
+
+## What is "Proj bridge to Java"
+
+_Proj bridge to Java_ is a small library of Java classes that wrap a few Proj functions
+by using the Java Native Interface (JNI). The main Java class is `org.proj4.PJ`.
+
+
+
+### Compilation
+
+To compile the native part, `configure` has to be run in the Proj directory like this:
+
+    CFLAGS=-Iinclude2 ./configure --with-jni=include1
+
+where
+
+* `include1` = folder in which the header file `jni.h` resides (usually `$JAVA_HOME/include`)
+* `include2` = folder in which the header file `jni_md.h` resides (usually `$JAVA_HOME/include/linux` or whatever)
+
+On MacOS, those two folders are `/Library/Java/JavaVirtualMachines/.../Contents/Home/include/`.
+
+
+The java part is compiled by running Ant inside the `jniwrap` folder.
+This will compile the classes and archive them in a JAR file.
+It applies to Linux, MacOS and Windows (and virtually to every system supporting java).
+
+
+
+### Requirements
+
+Beyond the ones already put by Proj, you need:
+
+* For compilation:
+  * Java 9+, the Java standard development kit version 9 or above
+  * Ant 1.9.8+, to run the build.
+* For execution:
+  * If a Java version less than the current version on the local machine is desired,
+    add an `release` attribute in the `javac` task of `build.xml`.
+
+
+
+### Documentation
+
+The documentation is held inside the code and can be retrieved by running
+doxygen inside the folder jniwrap. This will create the HTML format
+documentation inside of jniwrap/docs
+
+The standard way to achieve this is to use an Ant target:
+
+    ant do_make_help
+
+
+
+### License
+
+GPL for the first release.
+Proj.4 license for the second release.
+
+
+
+### Authors
+
+* Andrea Antonello (andrea.antonello@hydrologis.com)
+* Martin Desruisseaux (martin.desruisseaux@geomatys.com)
+
+
+
+## Usage & a fast example:
+
+The `proj.jar` is all is needed to implement Proj support in java applications.
+The whole job is done by the Proj library, so there are just a couple of functions that be used.
+
+The best way is to see everything through an example.
+In the following example we create two Coordinate Reference System and transform 3 points.
+The Coordinate Reference Systems and the points are hard-coded for simplicity.
+Of course, real applications would read them from a file or other data source.
+
+    import org.proj4.*;
+    import java.util.Arrays;
+
+    /**
+     * Converts coordinates from EPSG:32632 (WGS 84 / UTM zone 32N) to WGS84,
+     * then prints the result to the standard output stream.
+     */
+    public class Main {
+        public static void main(String[] args) throws PJException {
+            PJ sourcePJ = new PJ("+init=epsg:32632");           // (x,y) axis order
+            PJ targetPJ = new PJ("+proj=latlong +datum=WGS84"); // (λ,φ) axis order
+            double[] coordinates = {
+                500000,       0,   // First coordinate
+                400000,  100000,   // Second coordinate
+                600000, -100000    // Third coordinate
+            };
+            sourcePJ.transform(targetPJ, 2, coordinates, 0, 3);
+            System.out.println(Arrays.toString(coordinates));
+        }
+    }
+
+
+
+### compile the Main code
+
+we assume that Proj was compiled with the right flag to support the bridge to Java
+Therefore we have a library called `proj.jar`.
+Thus we compile the `Main.java` with the command:
+
+    javac -classpath <path to the jar library>/proj.jar Main.java
+
+and execute the created test case with:
+
+    java -cp .:<path to the jar library>/proj.jar -Djava.library.path=<path to the libproj, if needed> Main
+
+That's it, enjoy!