5.1.4 Convert Point Coordinates from Ghana War Office (feet)
Level of expertise required for this Chapter: Beginner; specifically for LUPMIS @ TCPD
This procedure can also be applied to different datum projections.
War Office in TM (Transverse Mercator) in feet is the standard projection on many sector maps of TCPD (see also Annex 8). As the precise definition of War Office is not available, this can be seen only as an approximation. War Office is actually the datum definition of the Ghana Grid, but commonly known in Ghana as the ‘War Office projection’. It is used in Ghana in some areas in feet (explained here), in other areas in meters.
1. Load Geographic Translator
(If not installed, contact TCPD-HQ / LUPMIS, email)
2. Input > Transverse Mercator > Output: UTM.
(Likewise, other projections can be chosen)
3. Datum (in the upper half of the screen): GHW Ghana WO 4_40/.99975/274320
(If not installed, contact TCPD-HQ / LUPMIS and copy file 3_param.dat to folder of Geographic Translator GeoTrans95)
4. Central Meridian: 1W
5. Origin Latitude: 4.6666666N
6. Scale Factor: 0.99975
7. False Easting: 274320
8. False Northing: 0
9. Easting value:
Take a pocket calculator and convert the feet to meter by dividing it by 3.28084 (as 1 ft = 0.30480 m) and enter the result in the Geographic Translator under Easting. (See also Annex 2.5 for conversions).
For example: If map reading shows: 1111610, divide by 3.28084, equals 338819.
10. Northing value: Repeat the same process (no.9 above) for northing
11. If converting to UTM or lat/long, check that the datum (at the bottom half of the screen) shows WGS84: World Geodetic System 1984
12. Convert button at the bottom.
13. Results are shown in the fields at the bottom
A more general description to convert between different projections (with an example to convert from lat / long to UTM) is given in Chapter 5.1.3.