How to use EPSG geodetic dataset

The EPSG geodetic dataset is a de-facto standard providing thousands of Coordinate Reference System (CRS) definitions together with information about how to perform coordinate operations, their accuracies and their domains of validity. The EPSG dataset is owned and maintained by the International Association of Oil & Gas producers. Usage of EPSG dataset with Apache SIS is optional but strongly recommended: without that geodetic dataset, only a small subset of CRS definitions will be available (basically the constants enumerated in the CommonCRS Java class) unless full definitions are provided in Well Known Text (WKT) or Geographic Markup Language (GML) formats. Furthermore, coordinate operations between any given pair of CRS may be less accurate and their domains of validity may be unspecified if Apache SIS can not query EPSG.

The EPSG geodetic dataset is not distributed with Apache SIS because the EPSG terms of use are incompatible with Apache license. The following items are quoted from those terms of use:

  • The EPSG Facilities are published by IOGP at no charge. Distribution for profit is forbidden.
  • The data may be included in any commercial package provided that any commerciality is based on value added by the provider and not on a value ascribed to the EPSG Dataset which is made available at no charge.
  • Ownership of the EPSG Dataset by IOGP must be acknowledged in any publication or transmission (by whatever means) thereof (including permitted modifications).
  • Modification of parameter values is permitted as described in the table 1 to allow change to the content of the information provided that numeric equivalence is achieved.
  • No data that has been modified other than as permitted in these Terms of Use shall be attributed to the EPSG Dataset.

In order to use the EPSG geodetic dataset with Apache SIS, apply one of the following choices:

Install a local copy with command-line tool

If the command-line tool has been downloaded and installed, just query any CRS. For example:

sis crs EPSG:6676

The first time that the command-line tool needs to query EPSG, it will prompt the user for authorization to download EPSG geodetic dataset from Maven Central. If the user accepts EPSG terms of use, then a local copy of the EPSG geodetic dataset will be created and stored in the apache-sis-0.7/data sub-directory.

If the command-line tool does not offer to download the EPSG geodetic dataset, try adding a derby-<version>.jar file (download lib-distribution from Derby project) in the apache-sis-0.7/lib sub-directory. This is normally not needed with Oracle JDK6, JDK7 or JDK8 because Apache SIS tries to use the JavaDB embedded in those distributions, but may be necessary with other distributions or in security-constrained environments.

For using the installed EPSG geodetic dataset in your own application, apply one of the following choices:

  • Set the SIS_DATA environment variable to the path to the apache-sis-0.7/data directory (preferred choice).
  • Set the derby.system.home Java property to the path to the apache-sis-0.7/data/Databases directory.

Alternatively SIS_DATA or derby.system.home can be set to the path of any other directory which contain the same files.

Add a Maven dependency

Maven projects can get the EPSG geodetic dataset automatically, without any prompt for terms of use agreement, if they add a dependency to the org.apache.sis.non-free:​sis-epsg:​0.7 artifact in their project. We assume that developers who add this dependency explicitely in their project agree with EPSG terms of use. The <dependency> fragment to use in pom.xml files is given in the download page.

In addition, users need to apply one of the following choices:

  • Set the SIS_DATA environment variable to the path of an initially empty directory (preferred choice).
  • Set the derby.system.home Java property to the path of an initially empty directory, or a directory that contain other Derby databases.
  • Register a DataSource under the java:comp/env/jdbc/SpatialMetadata name in a JNDI directory (see next section). The database must exist but can be initially empty.

The directory referenced by SIS_DATA or derby.system.home must exist. Sub-directories in that directory will be created as needed.

Use Java Naming and Directory Interface

While Apache SIS uses Apache Derby by default, it is also possible to use another database software like HSQL or PostgreSQL. The database must exist but can be empty, in which case it will be populated with an EPSG schema when first needed if the org.apache.sis.non-free:​sis-epsg:​0.7 dependency is on the classpath (see above section).

For using an arbitrary database, register a javax.sql.DataSource instance through the Java Naming and Directory Interface (JNDI). That registration can be done programmatically (by Java code) or by configuring XML files in some environments.

Registration by Java code

Registration can be done by the following Java code, provided that a JNDI implementation is available on the classpath:

// Example using PostgreSQL data source (org.postgresql.ds.PGSimpleDataSource)
PGSimpleDataSource ds = new PGSimpleDataSource();

// Registration assuming that a JNDI implementation is available
Context env = (Context) InitialContext.doLookup("java:comp/env");
env.bind("jdbc/SpatialMetadata", ds);

Registration in web application containers

JNDI implementations are provided by web application containers like Apache Tomcat. When Apache SIS is used in a JavaEE container, the data source can be configured as below:

  1. Make the JDBC driver available to the web container and its applications. On Tomcat, this is accomplished by installing the driver's JAR files into the $CATALINA_HOME/lib directory.

  2. If using Derby, copy derby.war into the $CATALINA_HOME/webapps directory and specify the directory where the Derby databases are located (skip this step if another database is used):

    export JAVA_OPTS=-Dderby.system.home=$SIS_DATA/Databases
  3. Declare the JNDI name in application WEB-INF/web.xml file:

      <description>EPSG dataset and other metadata used by Apache SIS.</description>
  4. Configure the data source in $CATALINA_HOME/conf/context.xml or in application META-INF/context.xml file (change attribute values as needed for the chosen JDBC driver):

    <Context crossContext="true">
      <Resource name            = "jdbc/SpatialMetadata"
                auth            = "Container"
                type            = "javax.sql.DataSource"
                username        = "sa"
                password        = "sa"
                driverClassName = "org.apache.derby.jdbc.EmbeddedDriver"
                url             = "jdbc:derby:SpatialMetadata"/>
  5. If using Derby, verify on the localhost:8080/derby/derbynet page (skip this step if another database is used).

More advanced configurations are possible. For example Tomcat can invoke a custom Java method instead than fetching the data source from the context.xml file.