[Proj] Is there any Java compatibility ??

Frank Warmerdam warmerdam at pobox.com
Wed Oct 25 07:52:12 EDT 2006

Sandeep Kumar Jakkaraju wrote:
> Is there any Java compatibility  ??
> Can I use proj4 lib functions in a Java program ??


The PROJ source tree includes JNI based Java bindings.  I have
attached the README from proj/jniwrap, but basically if you configure
with the --with-jni option properly, you should get jni wrappers.

The GeoTools projects also includes pure Java projections classes if
a JNI wrapped PROJ seems inconvenient.

Best regards,
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | President OSGeo, http://osgeo.org

-------------- next part --------------
   -------------------- J P R O J . 4 --------------------

This is the first release of a JNI wrap of the main proj4 functions.

PLEASE read the following information.

For more information regarding JPROJ4 please contact me through the 
web page at:



What is JPROJ4:

JPROJ is a small library of java classes that wrap a few proj functions by 
using the java native interface. 


To complile the native part, configure has to be run like this:
CFLAGS=-Iinclude2 ./configure --with-jni=include1
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)

The java part is compiled by running ant inside the "jniwrap" folder. 
This will compile the classes and archive them in a jar library.
It applies to Linux, Macos and Windows (and virtually to every system 
supporting java).


Beyond the ones already put by proj, you need:
- j2sdk, the java standard development kit
- ant, to run the build
- doxygen for the documentation generation


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 achive this is to use an ant target: 
ant do_make_help




Andrea Antonello (andrea.antonello at hydrologis.com)

Usage & a fast example:

The jproj.jar is all is needed to implement proj support in java applications.
The whole job is done by the proj4, 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 read projection informations and data from a file 
and then transform the data and query the information.

First step:
create a text file, let's say test.txt, with the following in it:
srcProj: +proj=latlong +datum=WGS84
destProj: +init=epsg:32632
rows: 1
46        11    194.0

This contains info about a source and destination projection, the number of data 
triplets and then the data (in this case just one point)

Step two:
create a test code. Simply copy the following into a file called Main.java. The 
code is commented to see what we are doing:

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.LinkedHashMap;

import org.proj4.Proj4;
import org.proj4.ProjectionData;

public class Main

  public static void main(String[] args) throws IOException
    // print out the usage if no argument was given
    if (args.length < 1)
      System.out.println("Usage:      Proj datafile");

    // now the input file is going to be read
    BufferedReader br = new BufferedReader(new InputStreamReader(
        new FileInputStream(new File(args[0]))));
    LinkedHashMap mapHeader = new LinkedHashMap();
    // read the header
    String line = null;
    for (int i = 0; i < 3; i++)
      if ((line = br.readLine()) != null)
        String[] header = line.split(":", 2);
        if (header.length <= 2)
          mapHeader.put(header[0].trim(), header[1].trim());
          System.out.println("Wrong file format");
    // with what you see above, the header was read
    // now I can define the number of rows of data triplets
    int rows = new Integer((String) mapHeader.get("rows")).intValue();
    double[][] testCoord = new double[rows][2];
    double[] testValues = new double[rows];
    System.out.println("Source coordinates and values:");

    // start reading the data
    for (int i = 0; i < rows; i++)
      if ((line = br.readLine()) != null)
        String[] values = line.split(" +");
        if (values.length == 3)
          testCoord[i][0] = new Double(values[0].trim()).doubleValue();
          testCoord[i][1] = new Double(values[1].trim()).doubleValue();
          testValues[i] = new Double(values[2].trim()).doubleValue();
          System.out.println("x = " + testCoord[i][0] + " y = "
              + testCoord[i][1] + " z = " + testValues[i]);
          System.out.println("Wrong file format or empty line found");

    // create the dataset
    // this is necessary to be able to transform
    ProjectionData dataTP = new ProjectionData(testCoord, testValues);

    // here we go with the instantiation of the proj4 object
    Proj4 testProjection = new Proj4((String) mapHeader.get("srcProj"),
        (String) mapHeader.get("destProj"));

    // the instantiation of the proj4 object instantiated also the projection 
    // objects for source and destination projection
    // therefore we can already print the projection infos:

    // and transform, passing as parameter the created dataset:
    testProjection.transform(dataTP, 1, 1);
    // if we need the parameters as Hashmap for a later use:
    LinkedHashMap testMap = testProjection.getSrcProjInfo();
    // and let us print them to screen to see them
    System.out.println("Proj as a Hashmap");



Step three
compile the Main code:
we assume that proj was compiled with the right flag to support jproj.
Therefore we have a library called jproj.jar.
Thus we compile the Main.java with the command:

javac -classpath <path to the jar library>/jproj.jar Main.java

and execute the created test case with:

java -cp .:<path to the jar library>/jproj.jar -Djava.library.path=<path to the libproj, if needed> Main test.txt

That's it, enjoy!

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