The issue is that the yellow dots should be fully overlapped with the black points (We are simply extracting Lat/long and elevation values from a Raster Image). The portion of the image where yellow dots are not overlapped means the data has not been extracted for those points. The no data has been handled in line "Double.isNaN(t.getDouble(j, i)". There is nothing in-memory We have converted everything back into disk and visualizing the image on QGIS, I have updated the code snippet with comments which might help you in further understanding. I appreciate you helping on this
public void testMethod(String rastedImageDir, String TAB_SEP, JavaSparkContext javaSparkContext) {
// List of file supported
List<String> tiffExtensions = new ArrayList<>();
tiffExtensions.add(".tif");
tiffExtensions.add(".TIF");
tiffExtensions.add(".tiff");
tiffExtensions.add(".TIFF");
// Creation of Options object to be passed to be used in HadoopGeoTiffRDD for reading Raster
final scala.Option<CRS> crsNone = scala.Option.apply(null);
final scala.Option<Object> objectNone = scala.Option.apply(null);
final scala.Option<Object> numPartitionsObject = scala.Option.apply(new Integer(10));
final scala.Option<Object> tileSize = scala.Option.apply(Integer.parseInt("256"));
final scala.Option<Object> partitionBytes = scala.Option.apply(128l * 1024 * 1024);
HadoopGeoTiffRDD.Options options = new HadoopGeoTiffRDD.Options$().apply(
JavaConverters.asScalaIteratorConverter(tiffExtensions.iterator()).asScala().toSeq(), crsNone,
HadoopGeoTiffRDD.GEOTIFF_TIME_TAG_DEFAULT(), HadoopGeoTiffRDD.GEOTIFF_TIME_FORMAT_DEFAULT(), tileSize,
numPartitionsObject, partitionBytes, objectNone);
// End of creation of Options object to be passed to be used in HadoopGeoTiffRDD
// Read the raster file from the directory and use the options object created in previous step
RDD<Tuple2<ProjectedExtent, Tile>> rasterImageRdd = HadoopGeoTiffRDD.spatial(new Path(rastedImageDir), options,
javaSparkContext.sc());
// convert to Java RDD
JavaRDD<Tuple2<ProjectedExtent, Tile>> rasterImageJavaRdd = rasterImageRdd.toJavaRDD();
// Extract Lat/Long value as a point and elevation value of each pixel of Raster Image
JavaRDD<String> pixelRdd = rasterImageJavaRdd
.flatMap(new FlatMapFunction<Tuple2<ProjectedExtent, Tile>, String>() {
private static final long serialVersionUID = -6395159549445351446L;
public Iterator<String> call(Tuple2<ProjectedExtent, Tile> v1) throws Exception {
ArrayList<String> list = new ArrayList<String>();
Tile t = v1._2;
ProjectedExtent projectedExtent = v1._1;
ProjectedRaster<CellGrid> r = new ProjectedRaster<CellGrid>(
new Raster<CellGrid>(t, projectedExtent.extent()), projectedExtent.crs());
GeometryFactory geometryFactory = new GeometryFactory(new PrecisionModel(), 4283);
WKTWriter wktWriter = new WKTWriter();
for (int i = 0; i < t.rows(); i++) {
for (int j = 0; j < t.cols(); j++) {
StringBuilder sb = new StringBuilder();
if (!Double.isNaN(t.getDouble(j, i))) {
Double elevation = t.getDouble(j, i);
Tuple2<Object, Object> longLatTupel = r.raster().rasterExtent().gridToMap(j, i);
if (longLatTupel._2() != null && longLatTupel._1() != null) {
Double latitude = Double.parseDouble(longLatTupel._2() + "");
Double longitude = Double.parseDouble(longLatTupel._1() + "");
Point point = geometryFactory.createPoint(new Coordinate(longitude, latitude));
sb.append(elevation).append(TAB_SEP);
sb.append(point);
list.add(sb.toString());
}
}
}
}
return list.iterator();
}
});
}
