Module org.apache.sis.referencing
Package org.apache.sis.referencing.operation.transform

Enum Class IterationStrategy

Object
Enum<IterationStrategy>
IterationStrategy
All Implemented Interfaces:
Serializable, Comparable<Iteration­Strategy>, Constable
public enum IterationStrategy extends Enum<IterationStrategy>
Strategy for iterating over the point arrays given to Abstract­Math­Transform​.transform(…) methods. If the source and destination arrays are the same and the region of the array to be written overlaps the region of the array to be read, it may be necessary to iterate over the points in reverse order or to copy some points in a temporary array. The suggest(…) method in this class returns a strategy suitable to the transform arguments.

Usage

The following code gives a skeleton for a Abstract­Math­Transform implementation capable to transform an array of double coordinates: 
    public class MyTransform extends AbstractMathTransform {
        @Override
        public void transform(double[] srcPts, int srcOff,
                              double[] dstPts, int dstOff, int numPts)
        {
            int srcInc = getSourceDimension();
            int dstInc = getTargetDimension();
            if (srcPts == dstPts) {
                switch (IterationStrategy.suggest(srcOff, srcInc, dstOff, dstInc, numPts)) {
                    case ASCENDING: {
                        break;
                    }
                    case DESCENDING: {
                        srcOff += (numPts-1) * srcInc; srcInc = -srcInc;
                        dstOff += (numPts-1) * dstInc; dstInc = -dstInc;
                        break;
                    }
                    default: {
                        srcPts = Arrays.copyOfRange(srcPts, srcOff, srcOff + numPts*srcInc);
                        srcOff = 0;
                        break;
                    }
                }
            }
            while (--numPts >= 0) {
                double x = srcPts[srcOff    ];
                double y = srcPts[srcOff + 1];
                double z = srcPts[srcOff + 2];
                // Repeat as many time as needed for dimension of input points.

                // Transform (x,y,z) here.

                dstPts[dstOff    ] = x;
                dstPts[dstOff + 1] = y;
                dstPts[dstOff + 2] = z;
                // Repeat as many time as needed for dimension of output points.

                srcOff += srcInc;
                dstOff += dstInc;
            }
        }
    }
Since:
0.5

  • Enum Constant Details

    • ASCENDING

      public static final IterationStrategy ASCENDING
      Iterate over the points in ascending index order. There is no need to copy the array.

    • DESCENDING

      public static final IterationStrategy DESCENDING
      Iterate over the points in descending index order. There is no need to copy the array.

    • BUFFER_SOURCE

      public static final IterationStrategy BUFFER_SOURCE
      Copy the points to transform in a temporary array before to apply the transform. The temporary array will be used for fetching the source coordinates.

      This algorithm can be used as a fallback for any unknown enumeration.

    • BUFFER_TARGET

      public static final IterationStrategy BUFFER_TARGET
      Write the transformed points in a temporary array and copies them to the destination subarray when the transformation is finished.

      Developers are allowed to ignore this value and fallback on the same algorithm than BUFFER_SOURCE, which is often easier to implement.

  • Method Details

    • values

      public static IterationStrategy[] values()
      Returns an array containing the constants of this enum class, in the order they are declared.
      Returns:
      an array containing the constants of this enum class, in the order they are declared

    • valueOf

      public static IterationStrategy valueOf(String name)
      Returns the enum constant of this class with the specified name. The string must match exactly an identifier used to declare an enum constant in this class. (Extraneous whitespace characters are not permitted.)
      Parameters:
      name - the name of the enum constant to be returned.
      Returns:
      the enum constant with the specified name
      Throws:
      Illegal­Argument­Exception - if this enum class has no constant with the specified name
      Null­Pointer­Exception - if the argument is null

    • suggest

      public static IterationStrategy suggest(int srcOff, int srcDim, int dstOff, int dstDim, int numPts)
      Suggests a strategy for iterating over the points to transform in an array. This convenience method is provided for transform method implementations. It makes the following assumptions:
      • Source and target array are the same.
      • For each coordinate to be transformed, all coordinate values are read before the transformation process starts. For example if a transform goes from geographic to projected CRS, the (longitude, latitude, height) tuple must be completely read before to start writing the (x,y,z) tuple.
      Parameters:
      src­Off - the offset in the source coordinate array.
      src­Dim - the dimension of input points.
      dst­Off - the offset in the destination coordinate array.
      dst­Dim - the dimension of output points.
      num­Pts - the number of points to transform.
      Returns:
      a strategy for iterating over the points during the transformation process.
      Throws:
      Arithmetic­Exception - if the given offsets or number of points are too high.