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I'm an architect, so not too well versed with all this datum/transformation talk.

My little problem: i want to be able to enter a position using UTM or deg/sec/min coordinates into google earth and fly there.

the cadastral maps we have come with eastings and northings and a general reference that reads: coordinates referred to Equator and 37* E (37deg E), all in meters

station:A +X (Easting):116379.70 -Y(Northing) : 6309.10

any help out there??

AndreJ
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Charles
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  • I've solved by going to a friend who used GEOCALC software wich is made in italy. You may give it a try. –  May 08 '14 at 23:43

2 Answers2

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UTM is surely not the right projection. UTM 37 is centered on 39°E, and has a false Easting of 500000 metres to that. South of the equator, UTM 37S is measuring from the south pole to avoid negative values.

Apart from UTM, there was a Cassini-Soldner projection (possibly in feet instead of metres), and a 5 degree wide "East Africa War" transverse mercator CRS used in earlier times.

Using a Cassini-Soldner projection centered on 37°E/0°N with ARC 1960 datum, I get for your point in WGS84:

38.046282° East 0.059779° South (decimal degrees)

located about 43km east of Nkubu town.

Based on the documents linked in Convert Cassini-Soldner Projection coordinates from Kenya to UTM I suggest to use the following proj.4 parameters for a custom CRS:

For the central meridian 37° (valid 36°-38°E)

+proj=cass +lat_0=0 +lon_0=37 +x_0=0 +y_0=0 +a=6378350.87 +rf=294.26 +towgs84=-306,-6,-101,0,0,0,0 +units=m +no_defs

For the central meridian 39° (valid 38°-40°E)

+proj=cass +lat_0=0 +lon_0=39 +x_0=0 +y_0=0 +a=6378350.87 +rf=294.26 +towgs84=-321,0,-135,0,0,0,0

Ellipsoid parameters are taken from Clifford Mugniers article, Datum shift parameters were computed from the coordinate tables in the document by Gordon Okumu Wayumba

AndreJ
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  • I have a similar query to the original poster. Your answer is promising, but can you expand on how you centred the projection? – chiyogami Apr 03 '16 at 16:33
  • @chiyogami Using QGIS, I had set up this custom CRS: +proj=cass +lat_0=0 +lon_0=37 +x_0=0 +y_0=0 +a=6378249.145 +b=6356514.96582849 +towgs84=-160,-6,-302,0,0,0,0 +units=m +no_defs. It contains the given center, and the ARC 1960 datum shift to WGS84. This is just a guess, and may need further investigation with known reference points. If you can provide more details, feel free to start a new question with those. – AndreJ Apr 03 '16 at 17:24
  • @chiyogami I updated my answer to reflect the documents linked in https://gis.stackexchange.com/questions/243642/convert-cassini-soldner-projection-coordinates-from-kenya-to-utm – AndreJ Jun 14 '17 at 18:50
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Datums and projections are fairly complex topics so in the long term I would recommend doing some research to develop a solid understanding of the concepts. To answer your current question you can use a UTM to Lat/Lon conversion tool that will do the transformations for you, here is one that I use from time to time:

UTM Lat/Lon calculator

Based on the information you provided I would guess that the UTM Zone of the coordinates is 37, this is important because Kenya crosses two UTM zones and you will need to know which zone the coordinates are in to properly convert from UTM to Lat/Lon.

However, be careful before you use this as there are many factors that will affect how accurate the calculations will be. If you need a high level of accuracy then you will need to determine what datum was used to create your source map and this may be difficult to sort out. This is not really critical if you only want to know the general area for the purposes of viewing the location on Google Earth.

dblanchett
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  • This answer could use some work - it doesn't provide much information. E.g. "there are many factors that will affect how accurate the calculations will be", without describing said factors. – Radar Oct 28 '13 at 16:18