Saturday, October 14, 2017

Origin Point for the grid system for Laconia Survey, Cavanagh, etc.

Users of Chapter 23 of the Laconia Survey, Cavanagh et al. [1996], etc. will probably be frustrated by the unnecessarily arcane Transverse Mercator system used by the authors.  Those who wish to use the location information in the book should be aware that the origin of their system (which they do not supply) is equivalent to  UTM:

34S, 619880.00 m E, 4091741.00 m N.

It is about 1300 m. N and slightly west of Mt. Taygetus.

In decimal lat/lon terms this is:  36.964135° N,  22.346662° E

(The absolute origin of their system is approximately 519880.00 m E, 3991741.00 m N in UTM.  The authors describe this as being to the SW of Cape Tainaron.  It is, in fact, to the SW of Cape Akritas.)

The value I have supplied for their origin is an approximation but very close to the real value and was obtained by manual iteration.  At any rate precision of placement is not a real goal for these authors since their coordinates designate 100 m. (1 hectare) squares.  Nevertheless the reader may use this origin value with some confidence and I believe it useful to locate most of their sites.


Here's an example from Cavanagh et al. [1996],  p. 289:

The Palace of the Despots in Mystràs is located at UTM:  621480.00 m E,  4104041.00 m N (the sector is 34S).  This value obtained by inspection in Google Earth.

The position given by them for this location is 1600 m E, 12300 m. N, which is to say, 1,600 m. E of their origin (given above) and 12300 meters N of their origin.   Adding these two values to the origin is:

Easting: 619880 + 1600 = 621480 (result in UTM, suitable for entering into Google Earth)
Northing: 4091741 + 12300 = 4104041 (UTM)

Setting the Tools> Options > Show Lat/Long to Universal Transverse Mercator and then creating a place mark with coordinates 621480, 4104041 will put the place mark on the Palace of Despots in Mystràs.


Cavanagh et al.  [2005]:  Cavanagh, Wiliam,  Christopher Mee, Peter James Neil Brodie and Tristan Carter.  'The Laconia Rural Sites Project', in The British School at Athens, Supplementary Volume 36, pp. iii-xv and 1-350, [2005].

Cavanagh et al. [1996]:  Cavanagh, William,  Joost Crouwel, R. W. V. Catling, Graham Shipley, Pamela Armstrong, Tristan Carter, David Hibler, Richard Jones, Jo Lawson, Marco Overbeek, Apostolos Sarris, Heleen Visscher And  Mark Ydo.  'Continuity And Change In A Greek Rural Landscape: The Laconia Survey. Volume II: Archaeological Data',  The British School at Athens. Supplementary Volumes, no. 27, pp. iii-xxx and 1-459.

1 comment:

  1. When reading the coordinates from the 1996 article 2 different sets of coordinates systems where used. The first one is based on the Greek Army Service and the second one i have no clue of.

    The GAS variant used in the article consist of 2 sets of 4 number. Example: The Palace of the Despots in Mystràs is shown as ¹016 ¹123. This means that the location is 101600 meters Eastings and 112300 meter Northings (instead of 1600m E and 12300m N used above).

    This also means that the GAS Absolute origin is: 519880.00m E, 3991741.00m Northings in *UTM N34*, not UTM S34.

    By adding the Eastings and Northings values to the values written in the article, you should be able to show the locations inside a GIS when using the UTM N34 Coordinate system.

    The Geodienst