getLetter100kID static method Null safety

String getLetter100kID(int column, int row, int parm)

Get the two-letter MGRS 100k designator given information translated from the UTM northing, easting and zone number.

@private @param {number} column the column index as it relates to the MGRS 100k set spreadsheet, created from the UTM easting. Values are 1-8. @param {number} row the row index as it relates to the MGRS 100k set spreadsheet, created from the UTM northing value. Values are from 0-19. @param {number} parm the set block, as it relates to the MGRS 100k set spreadsheet, created from the UTM zone. Values are from 1-60. @return {string} two letter MGRS 100k code.

Implementation

static String getLetter100kID(int column, int row, int parm) {
  // colOrigin and rowOrigin are the letters at the origin of the set
  var index = parm - 1;
  var colOrigin = unicode.toRune(SET_ORIGIN_COLUMN_LETTERS[index]);
  var rowOrigin = unicode.toRune(SET_ORIGIN_ROW_LETTERS[index]);
  // colInt and rowInt are the letters to build to return
  var colInt = colOrigin + column - 1;
  var rowInt = rowOrigin + row;
  var rollover = false;
  if (colInt > Z) {
    colInt = colInt - Z + A - 1;
    rollover = true;
  }
  if (colInt == I ||
      (colOrigin < I && colInt > I) ||
      ((colInt > I || colOrigin < I) && rollover)) {
    colInt++;
  }
  if (colInt == O ||
      (colOrigin < O && colInt > O) ||
      ((colInt > O || colOrigin < O) && rollover)) {
    colInt++;
    if (colInt == I) {
      colInt++;
    }
  }
  if (colInt > Z) {
    colInt = colInt - Z + A - 1;
  }
  if (rowInt > V) {
    rowInt = rowInt - V + A - 1;
    rollover = true;
  } else {
    rollover = false;
  }
  if (((rowInt == I) || ((rowOrigin < I) && (rowInt > I))) ||
      (((rowInt > I) || (rowOrigin < I)) && rollover)) {
    rowInt++;
  }
  if (((rowInt == O) || ((rowOrigin < O) && (rowInt > O))) ||
      (((rowInt > O) || (rowOrigin < O)) && rollover)) {
    rowInt++;
    if (rowInt == I) {
      rowInt++;
    }
  }
  if (rowInt > V) {
    rowInt = rowInt - V + A - 1;
  }
  var twoLetter =
      '${String.fromCharCode(colInt)}${String.fromCharCode(rowInt)}';
  return twoLetter;
}