Exactly - I am surprised he is surprised the coordinates are not spot on.

Anyway, after a bit of research,

"This is the cartographic projection system used in Egypt; Egypt
Transverse Mercator (ETM)

Designation: EGYPT RED BELT NORTH
Projection type: MERCATOR TRANSVERSE
Reference ellipsoid: HELMERT 1907
Semi-major axis: a = 6378200 m
Degree of flattening: 1/f = 298.300
Meridian of origin: GREENWICH "

The GPS GSM84 is offset from the Greenwich Meridian by about 97m at Greenwich - if the Egyptian system is based on this then the 'error' could be around 150m in Egypt (exagerated due to expansion of meridians towards the equator).

If ML was using survey data based on the Egyptian map grid then this may explain the discrepance. Strictly speaking you should always quote what system you are using when you quote coordinates.


Given the number of decimal places he is quoting to, it sounds like this is Total Station data - so may be tied into the local grid system rather than the GPS system.

Dave L




Edited 2 time(s). Last edit at 11/15/2006 07:11AM by Dave L.