5

I have some geo data from a collaborator with coordinates that look like this:

Grid    UTM X   UTM Y
30C10   696033  8967310
25C05   690997  8962938
25C05   690688  8962268

sometimes lower case (assume it's a typo?)

25c17   702859  8962900

and sometimes only one digit following the letter:

38c9    692363  8972661

These points should be in Zambia...

If I take just the first three characters as the UTM Zone (e.g. 38C) and use Perl's Geo::Coordinates::UTM to convert to WGS-84 it all looks very wrong.

Can anybody shed some light?

I am also asking the collaborator.

  • Did @AndreJoost's answer prove to be correct? The Zambia Lands Division has its own projection for UTM that they use for Zambia, which this might be from! – Simbamangu Jun 9 '16 at 14:36
  • @Simbamangu do you have any further information on this projection used by the Zambia Lands Division? – Oliver Burdekin Jun 18 at 14:09
6

I suggest to use UTM zone 35. The points fall inside the Zambia borders:

enter image description here

For UTM Zone 34 and 36, the points would be outside of the country, shifted horizontally into the next UTM zone.

The "Grid" could be some local kilometer-wide grid for finding streets and places. It seems to be build from a Northing coordinate, "c" and an Easting coordinate in kilometers:

enter image description here

This works for most points, except the northernmost.

  • Thank you very much - this works great for me now for demo purposes - I'll contact the contributors to be absolutely sure though. – uncoolbob May 14 '16 at 18:30
4

Zambia falls in the UTM zones 34 and 35 (quick check on Google Earth). The grid most probably refers to a grid of map sheets.

Looking at the X in the coordinates, the points should fall within zone 34. The X in zone 35 does not go over ~684,000 (again, this is based on looking at GE).

My answer is based on the information you provided and looking at GE.

Your best bet is to get back to the source of the data and get accurate info.

0

I have done some further digging into this and because Zambia traverses 3 UTM zones, it has been common practice in the past to use the UTM system with longitude 27o

"The common practice, in GIS, of using UTM system with longitude 27o east as central meridian for country-wide mapping is not supported by any scientific study with regards to the inherent errors and possible corrections."

This is from a Masters Thesis but may go some way to explaining odd CRSs coming out of Zambia.

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