@Override
  public void run() {
    amIActive = true;

    int progress;
    int row, col, i;
    int baseCol, baseRow, appendCol, appendRow;
    double x, y, z, zN, zBase, zAppend;
    double w1, w2, dist1, dist2, sumDist;
    boolean performHistoMatching = true;

    if (args.length <= 0) {
      showFeedback("Plugin parameters have not been set.");
      return;
    }

    // read the input parameters
    String inputBaseHeader = args[0];
    String inputHeader = args[1];
    String outputHeader = args[2];
    String resampleMethod = args[3].toLowerCase().trim();
    if (!resampleMethod.equals("nearest neighbour")
        && !resampleMethod.equals("bilinear")
        && !resampleMethod.contains("cubic")) {
      showFeedback("Resample method not recognized");
      return;
    }
    if (args[4].toLowerCase().contains("true")) {
      performHistoMatching = true;
    } else {
      performHistoMatching = false;
    }
    double power = Double.parseDouble(args[5]);
    if (power > 15.0) {
      power = 15.0;
    }
    if (power < 1.0) {
      power = 1.0;
    }

    try {

      // first perform histogram matching if necessary
      if (performHistoMatching) {
        String inputHeaderAdjusted = StringUtilities.replaceLast(inputHeader, ".dep", "_temp1.dep");
        histogramMatching(inputHeader, inputBaseHeader, inputHeaderAdjusted);
        inputHeader = inputHeaderAdjusted;
      }

      WhiteboxRaster baseRaster = new WhiteboxRaster(inputBaseHeader, "r");
      WhiteboxRaster appendRaster = new WhiteboxRaster(inputHeader, "r");

      double cellSizeX = baseRaster.getCellSizeX();
      double cellSizeY = baseRaster.getCellSizeY();
      double baseNoData = baseRaster.getNoDataValue();
      double appendNoData = appendRaster.getNoDataValue();
      double outputNoData = baseNoData;
      int baseCols = baseRaster.getNumberColumns();
      int baseRows = baseRaster.getNumberRows();
      int appendCols = appendRaster.getNumberColumns();
      int appendRows = appendRaster.getNumberRows();

      // figure out the north, south, east, and west coordinates and the rows and
      // columns of the output image.
      double baseNorth = baseRaster.getNorth();
      double baseSouth = baseRaster.getSouth();
      double baseEast = baseRaster.getEast();
      double baseWest = baseRaster.getWest();
      double baseNSRange = baseNorth - baseSouth;
      double baseEWRange = baseEast - baseWest;

      double appendNorth = appendRaster.getNorth();
      double appendSouth = appendRaster.getSouth();
      double appendEast = appendRaster.getEast();
      double appendWest = appendRaster.getWest();
      double appendNSRange = appendNorth - appendSouth;
      double appendEWRange = appendEast - appendWest;

      double north, south, east, west;

      if (baseNorth > baseSouth) {
        north = Double.NEGATIVE_INFINITY;
        south = Double.POSITIVE_INFINITY;

        if (baseNorth > north) {
          north = baseNorth;
        }
        if (appendNorth > north) {
          north = appendNorth;
        }
        if (baseSouth < south) {
          south = baseSouth;
        }
        if (appendSouth < south) {
          south = appendSouth;
        }
      } else {
        north = Double.POSITIVE_INFINITY;
        south = Double.NEGATIVE_INFINITY;

        if (baseNorth < north) {
          north = baseNorth;
        }
        if (appendNorth < north) {
          north = appendNorth;
        }
        if (baseSouth > south) {
          south = baseSouth;
        }
        if (appendSouth > south) {
          south = appendSouth;
        }
      }
      if (baseEast > baseWest) {
        east = Double.NEGATIVE_INFINITY;
        west = Double.POSITIVE_INFINITY;

        if (baseEast > east) {
          east = baseEast;
        }
        if (appendEast > east) {
          east = appendEast;
        }
        if (baseWest < west) {
          west = baseWest;
        }
        if (appendWest < west) {
          west = appendWest;
        }
      } else {
        east = Double.POSITIVE_INFINITY;
        west = Double.NEGATIVE_INFINITY;

        if (baseEast < east) {
          east = baseEast;
        }
        if (appendEast < east) {
          east = appendEast;
        }
        if (baseWest > west) {
          west = baseWest;
        }
        if (appendWest > west) {
          west = appendWest;
        }
      }

      // create the new destination image.
      int nRows = (int) Math.round(Math.abs(north - south) / cellSizeY);
      int nCols = (int) Math.round(Math.abs(east - west) / cellSizeX);

      WhiteboxRaster destination =
          new WhiteboxRaster(
              outputHeader,
              north,
              south,
              east,
              west,
              nRows,
              nCols,
              WhiteboxRasterBase.DataScale.CONTINUOUS,
              WhiteboxRasterBase.DataType.FLOAT,
              outputNoData,
              outputNoData);

      int nRowsLessOne = nRows - 1;

      // distance to edge images
      String distToEdgeBaseHeader =
          StringUtilities.replaceLast(inputBaseHeader, ".dep", "_temp1.dep");
      WhiteboxRaster distToEdgeBase =
          new WhiteboxRaster(
              distToEdgeBaseHeader,
              "rw",
              inputBaseHeader,
              WhiteboxRaster.DataType.FLOAT,
              Float.POSITIVE_INFINITY);
      distToEdgeBase.isTemporaryFile = true;

      double[] data;
      for (row = 0; row < baseRows; row++) {
        data = baseRaster.getRowValues(row);
        for (col = 0; col < baseCols; col++) {
          if (row == 0 || row == baseRows - 1) {
            distToEdgeBase.setValue(row, col, 0.0);
          } else if (col == 0 || col == baseCols - 1) {
            distToEdgeBase.setValue(row, col, 0.0);
          } else {
            if (data[col] != baseNoData) {
              if (data[col - 1] == baseNoData || data[col + 1] == baseNoData) {
                distToEdgeBase.setValue(row, col, 0.0);
              }
            } else {
              distToEdgeBase.setValue(row, col, 0.0);
            }
          }
        }
      }

      calculateDistance(distToEdgeBase);

      String distToEdgeAppendHeader =
          whitebox.utilities.StringUtilities.replaceLast(inputBaseHeader, ".dep", "_temp2.dep");
      WhiteboxRaster distToEdgeAppend =
          new WhiteboxRaster(
              distToEdgeAppendHeader,
              "rw",
              inputHeader,
              WhiteboxRaster.DataType.FLOAT,
              Float.POSITIVE_INFINITY);
      distToEdgeAppend.isTemporaryFile = true;

      for (row = 0; row < appendRows; row++) {
        data = appendRaster.getRowValues(row);
        for (col = 0; col < appendCols; col++) {
          if (row == 0 || row == appendRows - 1) {
            distToEdgeAppend.setValue(row, col, 0.0);
          } else if (col == 0 || col == appendCols - 1) {
            distToEdgeAppend.setValue(row, col, 0.0);
          } else {
            if (data[col] != appendNoData) {
              if (data[col - 1] == appendNoData || data[col + 1] == appendNoData) {
                distToEdgeAppend.setValue(row, col, 0.0);
              }
            } else {
              distToEdgeAppend.setValue(row, col, 0.0);
            }
          }
        }
      }

      calculateDistance(distToEdgeAppend);

      if (resampleMethod.contains("nearest")) {
        for (row = 0; row < nRows; row++) {
          for (col = 0; col < nCols; col++) {
            x = destination.getXCoordinateFromColumn(col);
            y = destination.getYCoordinateFromRow(row);

            baseCol = baseRaster.getColumnFromXCoordinate(x);
            baseRow = baseRaster.getRowFromYCoordinate(y);

            appendCol = appendRaster.getColumnFromXCoordinate(x);
            appendRow = appendRaster.getRowFromYCoordinate(y);

            zBase = baseRaster.getValue(baseRow, baseCol);
            zAppend = appendRaster.getValue(appendRow, appendCol);

            if (zBase != baseNoData && zAppend == appendNoData) {
              destination.setValue(row, col, zBase);
            } else if (zBase == baseNoData && zAppend != appendNoData) {
              destination.setValue(row, col, zAppend);
            } else if (zBase == baseNoData && zAppend == appendNoData) {
              destination.setValue(row, col, outputNoData);
            } else { // two valid values.

              // find the distance to the nearest edge in the base image
              dist1 = distToEdgeBase.getValue(baseRow, baseCol); // baseCol;
              dist2 = distToEdgeAppend.getValue(appendRow, appendCol); // appendCol;

              sumDist = Math.pow(dist1, power) + Math.pow(dist2, power);

              w1 = Math.pow(dist1, power) / sumDist;
              w2 = Math.pow(dist2, power) / sumDist;

              z = w1 * zBase + w2 * zAppend;

              destination.setValue(row, col, z);
            }
          }
          if (cancelOp) {
            cancelOperation();
            return;
          }
          progress = (int) (100f * row / nRowsLessOne);
          updateProgress("Resampling images: ", progress);
        }
      } else {
        if (destination.getDataType() != WhiteboxRaster.DataType.DOUBLE
            && destination.getDataType() != WhiteboxRaster.DataType.FLOAT) {
          showFeedback(
              "The destination image is not of an appropriate data"
                  + " type (i.e. double or float) to perform this operation.");
          return;
        }
        double dX, dY;
        double srcRow, srcCol;
        double originRow, originCol;
        double rowN, colN;
        double sumOfDist;
        double[] shiftX;
        double[] shiftY;
        int numNeighbours = 0;
        double[][] neighbour;
        if (resampleMethod.contains("cubic")) {
          shiftX = new double[] {-1, 0, 1, 2, -1, 0, 1, 2, -1, 0, 1, 2, -1, 0, 1, 2};
          shiftY = new double[] {-1, -1, -1, -1, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2};
          numNeighbours = 16;
          neighbour = new double[numNeighbours][2];
        } else { // resampleMethod is "bilinear"
          shiftX = new double[] {0, 1, 0, 1};
          shiftY = new double[] {0, 0, 1, 1};
          numNeighbours = 4;
          neighbour = new double[numNeighbours][2];
        }

        for (row = 0; row < nRows; row++) {
          for (col = 0; col < nCols; col++) {
            x = destination.getXCoordinateFromColumn(col);
            y = destination.getYCoordinateFromRow(row);

            baseCol = baseRaster.getColumnFromXCoordinate(x);
            baseRow = baseRaster.getRowFromYCoordinate(y);

            // what are the exact col and row of the image?
            srcRow = (baseNorth - y) / baseNSRange * (baseRows - 0.5);
            srcCol = (x - baseWest) / baseEWRange * (baseCols - 0.5);

            originRow = Math.floor(srcRow);
            originCol = Math.floor(srcCol);

            sumOfDist = 0;
            for (i = 0; i < numNeighbours; i++) {
              rowN = originRow + shiftY[i];
              colN = originCol + shiftX[i];
              neighbour[i][0] = baseRaster.getValue((int) rowN, (int) colN);
              dY = rowN - srcRow;
              dX = colN - srcCol;

              if ((dX + dY) != 0 && neighbour[i][0] != baseNoData) {
                neighbour[i][1] = 1 / (dX * dX + dY * dY);
                sumOfDist += neighbour[i][1];
              } else if (neighbour[i][0] == baseNoData) {
                neighbour[i][1] = 0;
              } else { // dist is zero
                neighbour[i][1] = 99999999;
                sumOfDist += neighbour[i][1];
              }
            }

            if (sumOfDist > 0) {
              z = 0;
              for (i = 0; i < numNeighbours; i++) {
                z += neighbour[i][0] * neighbour[i][1] / sumOfDist;
              }
              zBase = z;
            } else {
              zBase = baseNoData;
            }

            appendCol = appendRaster.getColumnFromXCoordinate(x);
            appendRow = appendRaster.getRowFromYCoordinate(y);

            srcRow = (appendNorth - y) / appendNSRange * (appendRows - 0.5);
            srcCol = (x - appendWest) / appendEWRange * (appendCols - 0.5);

            originRow = Math.floor(srcRow);
            originCol = Math.floor(srcCol);

            sumOfDist = 0;
            for (i = 0; i < numNeighbours; i++) {
              rowN = originRow + shiftY[i];
              colN = originCol + shiftX[i];
              neighbour[i][0] = appendRaster.getValue((int) rowN, (int) colN);
              dY = rowN - srcRow;
              dX = colN - srcCol;

              if ((dX + dY) != 0 && neighbour[i][0] != appendNoData) {
                neighbour[i][1] = 1 / (dX * dX + dY * dY);
                sumOfDist += neighbour[i][1];
              } else if (neighbour[i][0] == appendNoData) {
                neighbour[i][1] = 0;
              } else { // dist is zero
                neighbour[i][1] = 99999999;
                sumOfDist += neighbour[i][1];
              }
            }

            if (sumOfDist > 0) {
              z = 0;
              for (i = 0; i < numNeighbours; i++) {
                z += (neighbour[i][0] * neighbour[i][1]) / sumOfDist;
              }
              zAppend = z;
            } else {
              zAppend = appendNoData;
            }

            if (zBase != baseNoData && zAppend == appendNoData) {
              destination.setValue(row, col, zBase);
            } else if (zBase == baseNoData && zAppend != appendNoData) {
              destination.setValue(row, col, zAppend);
            } else if (zBase == baseNoData && zAppend == appendNoData) {
              destination.setValue(row, col, outputNoData);
            } else { // two valid values.

              // find the distance to the nearest edge in the base image
              dist1 = distToEdgeBase.getValue(baseRow, baseCol); // baseCol;
              dist2 = distToEdgeAppend.getValue(appendRow, appendCol); // appendCol;

              sumDist = dist1 + dist2;

              w1 = dist1 / sumDist;
              w2 = dist2 / sumDist;

              z = w1 * zBase + w2 * zAppend;

              destination.setValue(row, col, z);
            }
          }
          if (cancelOp) {
            cancelOperation();
            return;
          }
          progress = (int) (100f * row / nRowsLessOne);
          updateProgress("Resampling images: ", progress);
        }
      }

      destination.addMetadataEntry("Created by the " + getDescriptiveName() + " tool.");
      destination.addMetadataEntry("Created on " + new Date());

      destination.close();
      distToEdgeBase.close();
      distToEdgeAppend.close();
      baseRaster.close();

      if (performHistoMatching) {
        File header = new File(inputHeader);
        if (header.exists()) {
          header.delete();
        }
        File dataFile = new File(StringUtilities.replaceLast(inputHeader, ".dep", ".tas"));
        if (dataFile.exists()) {
          dataFile.delete();
        }
      } else {
        appendRaster.close();
      }

      returnData(outputHeader);

    } catch (OutOfMemoryError oe) {
      myHost.showFeedback("An out-of-memory error has occurred during operation.");
    } catch (Exception e) {
      myHost.showFeedback("An error has occurred during operation. See log file for details.");
      myHost.logException("Error in " + getDescriptiveName(), e);
    } finally {
      updateProgress("Progress: ", 0);
      // tells the main application that this process is completed.
      amIActive = false;
      myHost.pluginComplete();
    }
  }
  /** Used to execute this plugin tool. */
  @Override
  public void run() {
    amIActive = true;

    String streamsHeader;
    String pointerHeader;
    String outputFileName;
    int row, col, x, y;
    double xCoord, yCoord;
    int progress;
    int c;
    int[] dX = new int[] {1, 1, 1, 0, -1, -1, -1, 0};
    int[] dY = new int[] {-1, 0, 1, 1, 1, 0, -1, -1};
    double[] inflowingVals = new double[] {16, 32, 64, 128, 1, 2, 4, 8};
    boolean flag;
    double flowDir;
    double previousFlowDir;
    double linkLength;
    double streamValue;

    if (args.length <= 0) {
      showFeedback("Plugin parameters have not been set.");
      return;
    }

    streamsHeader = args[0];
    pointerHeader = args[1];
    outputFileName = args[2];

    // check to see that the inputHeader and outputHeader are not null.
    if ((streamsHeader == null) || (pointerHeader == null) || (outputFileName == null)) {
      showFeedback("One or more of the input parameters have not been set properly.");
      return;
    }

    try {
      WhiteboxRaster streams = new WhiteboxRaster(streamsHeader, "r");
      int rows = streams.getNumberRows();
      int cols = streams.getNumberColumns();
      double noData = streams.getNoDataValue();
      double gridResX = streams.getCellSizeX();
      double gridResY = streams.getCellSizeY();
      double diagGridRes = Math.sqrt(gridResX * gridResX + gridResY * gridResY);
      double[] gridLengths =
          new double[] {
            diagGridRes,
            gridResX,
            diagGridRes,
            gridResY,
            diagGridRes,
            gridResX,
            diagGridRes,
            gridResY
          };
      double east = streams.getEast() - gridResX / 2.0;
      double west = streams.getWest() + gridResX / 2.0;
      double EWRange = east - west;
      double north = streams.getNorth() - gridResY / 2.0;
      double south = streams.getSouth() + gridResY / 2.0;
      double NSRange = north - south;

      WhiteboxRaster pntr = new WhiteboxRaster(pointerHeader, "r");

      if (pntr.getNumberRows() != rows || pntr.getNumberColumns() != cols) {
        showFeedback("The input images must be of the same dimensions.");
        return;
      }

      DBFField fields[] = new DBFField[3];

      fields[0] = new DBFField();
      fields[0].setName("FID");
      fields[0].setDataType(DBFField.DBFDataType.NUMERIC);
      fields[0].setFieldLength(10);
      fields[0].setDecimalCount(0);

      fields[1] = new DBFField();
      fields[1].setName("STRM_VAL");
      fields[1].setDataType(DBFField.DBFDataType.NUMERIC);
      fields[1].setFieldLength(10);
      fields[1].setDecimalCount(3);

      fields[2] = new DBFField();
      fields[2].setName("Length");
      fields[2].setDataType(DBFField.DBFDataType.NUMERIC);
      fields[2].setFieldLength(10);
      fields[2].setDecimalCount(3);

      // set up the output files of the shapefile and the dbf
      ShapeFile output = new ShapeFile(outputFileName, ShapeType.POLYLINE, fields);

      byte numNeighbouringStreamCells;
      int FID = 0;
      for (row = 0; row < rows; row++) {
        for (col = 0; col < cols; col++) {
          streamValue = streams.getValue(row, col);
          if (streamValue > 0) {
            // see if it is a headwater location
            numNeighbouringStreamCells = 0;
            for (c = 0; c < 8; c++) {
              x = col + dX[c];
              y = row + dY[c];
              if (streams.getValue(y, x) > 0 && pntr.getValue(y, x) == inflowingVals[c]) {
                numNeighbouringStreamCells++;
              }
            }
            if (numNeighbouringStreamCells != 1) {
              // it's the start of a link.
              FID++;
              linkLength = 0;
              int[] parts = {0};
              PointsList points = new PointsList();
              x = col;
              y = row;
              previousFlowDir = -99;
              flag = true;
              do {
                // find the downslope neighbour
                flowDir = pntr.getValue(y, x);
                if (flowDir > 0) {
                  if (flowDir != previousFlowDir) {
                    // it's a bend in the stream so add this point
                    xCoord = west + ((double) x / cols) * EWRange;
                    yCoord = north - ((double) y / rows) * NSRange;
                    points.addPoint(xCoord, yCoord);

                    previousFlowDir = flowDir;
                  }

                  // update the row and column values to the
                  // cell that the flowpath leads to.
                  c = (int) (Math.log(flowDir) / LnOf2);
                  if (c > 7) {
                    showFeedback(
                        "An unexpected value has "
                            + "been identified in the pointer "
                            + "image. This tool requires a "
                            + "pointer grid that has been "
                            + "created using either the D8 "
                            + "or Rho8 tools.");
                    return;
                  }

                  x += dX[c];
                  y += dY[c];

                  linkLength += gridLengths[c];

                  if (streams.getValue(y, x) <= 0) { // it's not a stream cell
                    flag = false;
                  } else {
                    // is it a confluence
                    numNeighbouringStreamCells = 0;
                    int x2, y2;
                    for (int d = 0; d < 8; d++) {
                      x2 = x + dX[d];
                      y2 = y + dY[d];
                      if (streams.getValue(y2, x2) > 0
                          && pntr.getValue(y2, x2) == inflowingVals[d]) {
                        numNeighbouringStreamCells++;
                      }
                    }
                    if (numNeighbouringStreamCells > 1) {
                      // It's a confluence and you should stop here.
                      flag = false;
                    }
                  }

                } else {
                  flag = false;
                }

                if (!flag) {
                  // it's the end of the stream link so
                  // add the point.
                  xCoord = west + ((double) x / cols) * EWRange;
                  yCoord = north - ((double) y / rows) * NSRange;
                  points.addPoint(xCoord, yCoord);
                }

              } while (flag);

              // add the line to the shapefile.
              PolyLine line = new PolyLine(parts, points.getPointsArray());
              Object[] rowData = new Object[3];
              rowData[0] = new Double(FID);
              rowData[1] = new Double(streamValue);
              rowData[2] = new Double(linkLength / 1000.0);
              output.addRecord(line, rowData);
            }
          }
        }
        if (cancelOp) {
          cancelOperation();
          return;
        }
        progress = (int) (100f * row / (rows - 1));
        updateProgress(progress);
      }
      output.write();

      pntr.close();
      streams.close();

      // returning a header file string displays the image.
      returnData(outputFileName);

    } catch (OutOfMemoryError oe) {
      myHost.showFeedback("An out-of-memory error has occurred during operation.");
    } catch (Exception e) {
      myHost.showFeedback("An error has occurred during operation. See log file for details.");
      myHost.logException("Error in " + getDescriptiveName(), e);
    } finally {
      updateProgress("Progress: ", 0);
      // tells the main application that this process is completed.
      amIActive = false;
      myHost.pluginComplete();
    }
  }