code: public static @Nonnull double[][] fromJsonJLineString(@Nonnull JsonArray lineString) {
          double[][] result = new double[lineString.size()][lineString.get(0).asArray().size()];
          for(int i =0; i<lineString.size();i++) {
              JsonArray subArray = lineString.get(i).asArray();
              for(int j =0; j<subArray.size();j++) {
                  result[i][j] = subArray.get(j).asPrimitive().asDouble();
              }
          }
          return result;
      }
docs: Convert json array of arrays of double primitives to a double[][].
  @param lineString 2d JsonArray of doubles
  @return a double[][] 2d array of doubles