Welcome Geomajas Developers¶
Geomajas is a Java based client-server GIS framework for the web, that leverages the GeoTools library on the back end. Although Geomajas has it’s own Object model, many functionalities rely quite heavily on the GeoTools library.
Geomajas is very Spring oriented which results in a lot of Spring services that use GeoTools under the hood. Often the Geomajas interfaces will depend upon GeoTools objects (as parameters in the methods, or return types).
This page covers some specific examples of how and where the Geomajas framework leverages GeoTools, and how to actually use or acquire those GeoTools components.
Plugin: GeoTools Layer¶
One of the implementations of the Geomajas object model consists of a wrapper around the GeoTools feature model. Through this ‘layer’, any GeoTools vector DataStore can be used to supply vector data to a Geomajas layer.
More information on this specific plug-in can be found here:
Plugin: Hibernate Spatial Layer¶
Geomajas also supports a Hibernate Spatial based layer:
This layer allows the use of complex feature attributes based on many-to-one and one-to-many entity relationships by exploiting the POJO capabilities of Hibernate.
For filtering, Geomajas uses the
gt-opengis Filter object model and the GeoTools ECQL standard. In
order to create Filter objects for a specific Geomajas layer, there is the FilterService
interface. By default a Spring bean for that service will always be available on the classpath,
so it can always be auto wired.
The FilterService provides convenience methods for quickly creating OpenGIS Filter objects which can then be used in Geomajas (or GeoTools) layers.
@Autowired private FilterService filterService; .... Filter filter = filterService.parseFilter("<ECQL filter string>"); filter = and(filter, filterService.createWithinFilter(geometry, geometryName));
To work with all coordinate systems known to Geomajas, one must use the GeoService provided by Geomajas.
For defining coordinate systems and transformations between those coordinate systems, the GeoTools library is used. That being said, Geomajas provides the ability to register extra coordinate systems through the Spring configuration. As a result those new coordinate systems are available only through Geomajas GeoService interface (and not when directly using the GeoTools CRS helper class).
This GeoService specifically handles CRS transformations with support for transformable areas. These transformable areas define the boundaries wherein transformations between 2 coordinate systems are supported. This way unexpected transformation exceptions are avoided.