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I'm in the process of adding automatic CRS conversion to a Spark application and running into some problems with the implementation.

Each row in a dataframe that is being converted will contain columns Latitude, Longitude, and EPSGCode and will result in new columns for the converted Lat/Long in WGS84.

Spark itself isn't the issue (included for context only), as wiring this up to run within a UDF is fairly simple.

Right now, I'm running into issues with a common conversion, given EPSGCode 4267 and targeting 4326, I either get an error or just get back the original coordinates.

I've tried two libraries...

OrbisGIS CTS: https://github.com/orbisgis/cts (throws error)

Proj4j: https://github.com/locationtech/proj4j (returns same points)

Here's a sample of my scala code using CTS:


class DatumConversionSpec extends FunSpec {

  val cRSFactory = new CRSFactory()
  val registryManager: RegistryManager = cRSFactory.getRegistryManager
  registryManager.addRegistry(new EPSGRegistry)

  def getCRSFromEpsgCode(code: Int): GeodeticCRS = cRSFactory.getCRS(s"EPSG:$code").asInstanceOf[GeodeticCRS]

  it("handles NAD27 to WGS84 conversion") {

    val source = getCRSFromEpsgCode(4267)
    val target = getCRSFromEpsgCode(4326)

    println(source)
    println(target)

    // throws exception here!!!
    val ops = CoordinateOperationFactory.createCoordinateOperations(source, target)

    val op = CoordinateOperationFactory.getMostPrecise(ops)

    .....

which throws the exception java.lang.IllegalArgumentException: No transformation found from EPSG:4267 to EPSG:4326.

When using proj4j I just got back the original coordinates.

Is there another library that could recommended for this or a different approach I should be taking?

note: our Spark infrastructure runs Scala 2.11.8 currently against Java 8. Upgrading to a newer Java version to use another library is not an option right now

  • Turns out I get the same failure going from NAD83 to WGS84 as well. – Ron DeFreitas Sep 4 '19 at 16:00
  • With proj4j, does the nad27 / 4267 definition include a +towgs84 parameter? CTS says for NAD27 that it needs file-based tfm and that's not implemented yet. It might be possible to add a three or seven parameter tfm instead into its definition but it won't be very accurate. – mkennedy Sep 4 '19 at 23:20
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Answer using Proj4J.

Better accomplish this task in a two-step datum transform,

First

NAD27 to NAD83

and then

NAD83 to WGS84

or not, considering you can assimilate NAD83 and WGS84 to be the same, depending on your accuracy requirements.

In any case, for that you'll have to download the corresponding datum grids from,

https://github.com/OSGeo/proj-datumgrid

(scroll-down to see a detailed description of every grid, in order to choose the ones you're going to download)

After that, copy them to this folder of your source tree

https://github.com/locationtech/proj4j/tree/master/src/main/resources/proj4/nad

and then, build Proj4J with the grids included.

From the following code snippet you can see Proj4J is going to try opening these grid files.

static {
    Datum temp = new Datum("NAD27", new ArrayList<Grid>(), Ellipsoid.CLARKE_1866, "North_American_Datum_1927");
    try {
        temp = new Datum("NAD27", Grid.fromNadGrids("@conus,@alaska,@ntv2_0.gsb,@ntv1_can.dat"), Ellipsoid.CLARKE_1866, "North_American_Datum_1927");
    } catch (IOException e) {
        // TODO: Logging
    }
    NAD27 = temp;
}

https://github.com/locationtech/proj4j/blob/master/src/main/java/org/locationtech/proj4j/datum/Datum.java

And there you have the confirmation of the grids you're going to need!

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