[Proj] WGS84 to NAD27 Coordinate conversion in Android

[Martin Desruisseaux]

Hello Robb

I you look for a pure Java implementation, Apache Spatial Information
System (http://sis.apache.org/) can do this coordinate transformation.
Apache SIS is a source of inspiration for the new PROJ version
(https://gdalbarn.com/) in progress. Pros and cons below:

Advantages:

  * Strong emphasis on OGC and ISO standards, including GML, WKT 1 and
    2, etc.
  * Advanced features not found even in Proj.4 (late-binding
    implementation, etc.). PROJ is catching-up with gdalbarn however.
  * You can use it in a way that does not make you too dependent on this
    particular implementation, through GeoAPI interfaces.

Inconvenient:

  * Not as many projections than Proj.
  * Relatively large binary (~3 Mb) with many features not needed for
    WGS84 to NAD27 UTM transformations.
  * Depends on JAXB, which is not available by default on Android.
  * Making sure that SIS runs on Android would probably require more work.

The JAR size problem may be mitigated by trimming down the classes not
needed by your application. I think Maven Shader plugin can do that.
Since Java 9, jlink can also do that but the result is a native binary
instead than a portable Java Archive file. A Google Summer of Code
student started a port of SIS to Android (e.g. removing JAXB
dependencies), but this work has not been completed.

Let me know if you wish any additional information,

    Martin


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