Programming with JViews Maps > Creating a Map Application Using the API > Handling Spatial Reference Systems > Converting Between Two Spatial Reference Systems

Converting Between Two Spatial Reference Systems

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The conversion between two Spatial Reference Systems (SRS) is performed by a coordinate transformation, that is, a mathematical transformation or a chain of mathematical transformations.

For example, when superimposing Global Positioning System (GPS) points (expressed in longitude and latitude) on a state map (where coordinates are expressed in meters, in UTM projection), the GPS coordinates are expressed in a geographic coordinate system, while the state map coordinates are in a projected coordinate system. Once the SRS for each data source is known, the JViews Maps package is able to construct a mathematical transformation to convert from one coordinate system to another.

SRS and coordinate transformations are mainly used for two purposes.

The first one is to render the pipeline of the reader framework, and the main steps are:

  1. Defining the source SRS
    2. The SRS of source data is often stored in the reader or in the feature of the iterator that is used. If not, the reader provides the setSourceCoordinateSystem() method. The SRS of source data is stored in map features returned by the iterator.
  2. Defining the target SRS
    3. The SRS of target data is optional. In fact, the rendering mechanism only needs a coordinate transformation. Before rendering your graphic objects, you have to create the coordinate transformation once.
  3. Creating the coordinate transformation
    4. If no coordinate transformation is needed, the rendering can be performed using an identity transformation.
  4. Iterating on map features provided by the iterator, and rendering them.

The second one is to position free data, (without the renderers, you create the coordinate of the graphic object yourself), and the main steps are nearly the same:

  1. Defining the source SRS.
  2. Defining the target SRS.
  3. Creating the coordinate transformation.
  4. Transforming each coordinate manually.

The following packages define some useful SRS to be used with maps:

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