function getMinNorthing(zoneLetter) {
    var northing;
    switch (zoneLetter) {
    case 'C':
      northing = 1100000.0;
      break;
    case 'D':
      northing = 2000000.0;
      break;
    case 'E':
      northing = 2800000.0;
      break;
    case 'F':
      northing = 3700000.0;
      break;
    case 'G':
      northing = 4600000.0;
      break;
    case 'H':
      northing = 5500000.0;
      break;
    case 'J':
      northing = 6400000.0;
      break;
    case 'K':
      northing = 7300000.0;
      break;
    case 'L':
      northing = 8200000.0;
      break;
    case 'M':
      northing = 9100000.0;
      break;
    case 'N':
      northing = 0.0;
      break;
    case 'P':
      northing = 800000.0;
      break;
    case 'Q':
      northing = 1700000.0;
      break;
    case 'R':
      northing = 2600000.0;
      break;
    case 'S':
      northing = 3500000.0;
      break;
    case 'T':
      northing = 4400000.0;
      break;
    case 'U':
      northing = 5300000.0;
      break;
    case 'V':
      northing = 6200000.0;
      break;
    case 'W':
      northing = 7000000.0;
      break;
    case 'X':
      northing = 7900000.0;
      break;
    default:
      northing = -1.0;
    }
    if (northing >= 0.0) {
      return northing;
    }
    else {
      throw ("Invalid zone letter: " + zoneLetter);
    }

  }
The function getMinNorthing returns the minimum northing value of a MGRS
zone.

Ported from Geotrans' c Lattitude_Band_Value structure table.

@private
@param {char} zoneLetter The MGRS zone to get the min northing for.
@return {number}