private void calculateDistance(WhiteboxRaster outputImage) {
    String outputHeader = outputImage.getHeaderFile();
    int row, col, whichCell, i, x, y;
    double z, z2, zMin, h = 0;
    double infVal = Float.POSITIVE_INFINITY;
    int[] dX = new int[] {-1, -1, 0, 1, 1, 1, 0, -1};
    int[] dY = new int[] {0, -1, -1, -1, 0, 1, 1, 1};
    int[] Gx = new int[] {1, 1, 0, 1, 1, 1, 0, 1};
    int[] Gy = new int[] {0, 1, 1, 1, 0, 1, 1, 1};
    int progress;

    int rows = outputImage.getNumberRows();
    int cols = outputImage.getNumberColumns();
    double noData = outputImage.getNoDataValue();
    double gridRes = (outputImage.getCellSizeX() + outputImage.getCellSizeY()) / 2;

    WhiteboxRaster Rx =
        new WhiteboxRaster(
            outputHeader.replace(".dep", "_temp1.dep"),
            "rw",
            outputHeader,
            WhiteboxRaster.DataType.FLOAT,
            0);
    Rx.isTemporaryFile = true;
    WhiteboxRaster Ry =
        new WhiteboxRaster(
            outputHeader.replace(".dep", "_temp2.dep"),
            "rw",
            outputHeader,
            WhiteboxRaster.DataType.FLOAT,
            0);
    Ry.isTemporaryFile = true;

    for (row = 0; row < rows; row++) {
      for (col = 0; col < cols; col++) {
        z = outputImage.getValue(row, col);
        if (z != 0) {
          zMin = infVal;
          whichCell = -1;
          for (i = 0; i <= 3; i++) {
            x = col + dX[i];
            y = row + dY[i];
            z2 = outputImage.getValue(y, x);
            if (z2 != noData) {
              switch (i) {
                case 0:
                  h = 2 * Rx.getValue(y, x) + 1;
                  break;
                case 1:
                  h = 2 * (Rx.getValue(y, x) + Ry.getValue(y, x) + 1);
                  break;
                case 2:
                  h = 2 * Ry.getValue(y, x) + 1;
                  break;
                case 3:
                  h = 2 * (Rx.getValue(y, x) + Ry.getValue(y, x) + 1);
                  break;
              }
              z2 += h;
              if (z2 < zMin) {
                zMin = z2;
                whichCell = i;
              }
            }
          }
          if (zMin < z) {
            outputImage.setValue(row, col, zMin);
            x = col + dX[whichCell];
            y = row + dY[whichCell];
            Rx.setValue(row, col, Rx.getValue(y, x) + Gx[whichCell]);
            Ry.setValue(row, col, Ry.getValue(y, x) + Gy[whichCell]);
          }
        }
      }
      if (cancelOp) {
        cancelOperation();
        return;
      }
      progress = (int) (100f * row / (rows - 1));
      updateProgress("Calculating distances: ", progress);
    }

    for (row = rows - 1; row >= 0; row--) {
      for (col = cols - 1; col >= 0; col--) {
        z = outputImage.getValue(row, col);
        if (z != 0) {
          zMin = infVal;
          whichCell = -1;
          for (i = 4; i <= 7; i++) {
            x = col + dX[i];
            y = row + dY[i];
            z2 = outputImage.getValue(y, x);
            if (z2 != noData) {
              switch (i) {
                case 5:
                  h = 2 * (Rx.getValue(y, x) + Ry.getValue(y, x) + 1);
                  break;
                case 4:
                  h = 2 * Rx.getValue(y, x) + 1;
                  break;
                case 6:
                  h = 2 * Ry.getValue(y, x) + 1;
                  break;
                case 7:
                  h = 2 * (Rx.getValue(y, x) + Ry.getValue(y, x) + 1);
                  break;
              }
              z2 += h;
              if (z2 < zMin) {
                zMin = z2;
                whichCell = i;
              }
            }
          }
          if (zMin < z) {
            outputImage.setValue(row, col, zMin);
            x = col + dX[whichCell];
            y = row + dY[whichCell];
            Rx.setValue(row, col, Rx.getValue(y, x) + Gx[whichCell]);
            Ry.setValue(row, col, Ry.getValue(y, x) + Gy[whichCell]);
          }
        }
      }
      if (cancelOp) {
        cancelOperation();
        return;
      }
      progress = (int) (100f * (rows - 1 - row) / (rows - 1));
      updateProgress("Calculating distances: ", progress);
    }

    //        for (row = 0; row < rows; row++) {
    //            for (col = 0; col < cols; col++) {
    //                z = outputImage.getValue(row, col);
    //                outputImage.setValue(row, col, Math.sqrt(z) * gridRes);
    //            }
    //            if (cancelOp) {
    //                cancelOperation();
    //                return;
    //            }
    //            progress = (int) (100f * row / (rows - 1));
    //            updateProgress(progress);
    //        }

    outputImage.flush();
    Rx.close();
    Ry.close();
  }
  @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();
    }
  }