GeoMesa Transformations Example

This tutorial shows how to use GeoTools to select and modify the attributes returned from a query.

About this Tutorial

In the spirit of keeping things simple, the code in this tutorial only does a few small things:

  1. Demonstrate basic queries against GeoMesa

  2. Demonstrate projection queries against GeoMesa

  3. Demonstrate transformation queries against GeoMesa

These terms are potentially ambiguous, so we will describe them next.


GeoMesa allows users to perform relational projections on query results. Projection is an overloaded term; when we use it here, we refer to the relational sense. Although projections can also modify an attribute’s value, in this tutorial we will refer to such modifications as transformations to keep things clearer.

Projections and transformations have the following uses and advantages:

  1. Subset to specified columns - reduces network overhead of returning results

  2. Rename specified columns - alters the schema of data on the fly

  3. Compute new attributes from one or more original attributes - adds derived fields to results

When possible, projections and transformations are applied in parallel across the back-end cluster, thus making them very fast. They are analogous to the map tasks in a map-reduce job. Transformations are also extensible; developers can implement new functions and plug them into the system using standard mechanisms from Geotools.

Choice of Backing Storage

This tutorial will work with several different back-ends. For simplicity, the rest of the tutorial will assume the use of HBase. Alternatively, you may use Accumulo, Cassandra, Redis, or the GeoMesa FileSystem DataStore. If not using HBase, the commands in the rest of the tutorial will vary slightly.


Before you begin, you must have the following:

  • Java JDK 1.8

  • Apache Maven 3.6 or later

  • a GitHub client

  • Completion of the GeoMesa quick start for your choice of back end


This tutorial will use the data you wrote in the initial quick start, so make sure you complete that first.

Download and Build the Tutorial

Pick a reasonable directory on your machine, and run:

$ git clone
$ cd geomesa-tutorials


Make sure that you download or checkout the version of the tutorials project that corresponds to your GeoMesa version. See About Tutorial Versions for more details.

To ensure that the tutorial works with your environment, modify the pom.xml to set the appropriate versions for HBase, Hadoop, etc.

For ease of use, the project builds a bundled artifact that contains all the required dependencies in a single JAR. To build, run:

$ mvn clean install -pl geomesa-tutorials-hbase/geomesa-tutorials-hbase-transforms -am


The module name will vary depending on choice of back end.

Run the Tutorial

On the command-line, run:

$ java -cp geomesa-tutorials-hbase/geomesa-tutorials-hbase-transforms/target/geomesa-tutorials-hbase-transforms-$VERSION.jar \
    org.geomesa.example.hbase.transformations.HBaseQueryTutorial \
    --hbase.zookeepers <zookeepers>                              \
    --hbase.catalog <table>

where you provide the following arguments:

  • <zookeepers> the HBase Zookeeper quorum. If you installed HBase in stand-alone mode, this will be localhost. Note that for most use cases, it is preferable to put the hbase-site.xml from your cluster on the GeoMesa classpath instead of specifying Zookeepers.

  • <table> the name of the table that holds your quick-start data


The path, class name, and required arguments will vary depending on choice of back end.

The code will query GeoMesa using various projections and transforms and print out the results.

Looking at the Code

The source code is meant to be accessible for this tutorial. The main logic is contained in the generic org.geomesa.example.transformations.GeoMesaQueryTutorial in the geomesa-tutorials-common module, which is datastore agnostic. Some relevant methods:

  • basicQuery executes a base filter without any further options. All attributes are returned in the data set.

  • basicProjectionQuery executes a base filter but specifies a subset of attributes to return.

  • basicTransformationQuery executes a base filter and transforms one of the attributes that is returned.

  • renamedTransformationQuery executes a base filter and transforms one of the attributes, returning it in a separate derived attribute.

  • mutliFieldTransformationQuery executes a base filter and transforms two attributes into a single derived attributes.

  • geometricTransformationQuery executes a base filter and transforms the geometry returned from a point into a polygon by buffering it.

Additional transformation functions are listed here.

Please note that currently not all functions are supported by GeoMesa.

Basic query with no projections

This query does not use any projections or transformations. Note that all attributes are returned in the results.

Query query = new Query(simpleFeatureTypeName, cqlFilter);

Query with a projection for two attributes

This query uses a projection to only return the ‘Actor1Name’ and ‘geom’ attributes.

String[] properties = new String[] { "Actor1Name", "geom" };
Query query = new Query(simpleFeatureTypeName, cqlFilter, properties);

Sample Output




POINT (32 49)

Query with an attribute transformation

This query performs a transformation on the ‘Actor1Name’ attribute, to print it in a more user-friendly format.

String[] properties = new String[] { "geom", "Actor1Name=strCapitalize(Actor1Name)" };
Query query = new Query(simpleFeatureTypeName, cqlFilter, properties);

Sample Output



POINT (30.5167 50.4333)

United States

Query with a derived attribute

This query creates a new attribute called ‘derived’ based off a join of the ‘Actor1Name’ and ‘Actor1Geo_FullName’ attribute. This could be used to show the actor and location of the event, for example.

String property = "derived=strConcat(Actor1Name,strConcat(' - ',Actor1Geo_FullName))";
String[] properties = new String[] { geom, property };
Query query = new Query(simpleFeatureTypeName, cqlFilter, properties);

Sample Output



POINT (30.5167 50.4333)

UNITED STATES - Kyiv, Kyyiv, Misto, Ukraine

Query with a geometric transformation

This query performs a geometric transformation on the points returned, buffering them by a fixed amount. This could be used to estimate an area of impact around a particular event, for example.

String[] properties = new String[] { "geom", "derived=buffer(geom, 2)" };
Query query = new Query(simpleFeatureTypeName, cqlFilter, properties);

Sample Output



POINT (30.5167 50.4333)

POLYGON ((32.5167 50.4333, 32.478270560806465 50.04311935596775, 32.36445906502257 49.66793313526982, 32.17963922460509 49.3221595339608, 31.930913562373096 49.01908643762691, 31.627840466039206 48.77036077539491, 31.28206686473018 48.58554093497743, 30.906880644032256 48.47172943919354, 30.5167 48.4333, 30.126519355967744 48.47172943919354, 29.75133313526982 48.58554093497743, 29.405559533960798 48.77036077539491, 29.102486437626904 49.01908643762691, 28.85376077539491 49.3221595339608, 28.668940934977428 49.66793313526983, 28.55512943919354 50.04311935596775, 28.5167 50.4333, 28.55512943919354 50.82348064403226, 28.668940934977428 51.198666864730185, 28.85376077539491 51.54444046603921, 29.102486437626908 51.8475135623731, 29.405559533960798 52.09623922460509, 29.751333135269824 52.281059065022575, 30.126519355967748 52.39487056080647, 30.516700000000004 52.4333, 30.906880644032263 52.39487056080646, 31.282066864730186 52.281059065022575, 31.62784046603921 52.09623922460509, 31.9309135623731 51.847513562373095, 32.1796392246051 51.5444404660392, 32.36445906502258 51.19866686473018, 32.478270560806465 50.82348064403225, 32.5167 50.4333))