Title: projection woes for madagascar.
Many thanks to Sam Knight and Spencer Simpson for their replies..
 
There is'nt a definitive sum to this posting, but  it raises an issue i'd thought i'd share with other listers (esp. if you are working in madagascar)
 
Basically the projection information is as posted on many internet docs:

projection :   oblique Mercator  (hotine)
datum  :   Tananarive_1925
spheroid:    international 1924
Origin long :  46.43722917
Origin Latt:    -18.9
Azimuth:   18.9
scale factor:   0.9995
false east :   400000
false north :  800000
units:    m.

which would suggest a PRJ file entry of:

"Laborde CS", 7, 147, 7,  46.43722917, -18.9, 18.9, 0.9995, 400000, 800000

However..this doesnt work for me, the false easting and northing needed to be 'adjusted' for my data to work (thanks Spencer). I therefore assumed that my data 'supplier' had fudged the  coordinates in the map information thereby ruining the  chances of the data projecting properly........BUT  on testing the original data and the projection info  in ArcGIS 9 i find  everything works fine....Madagascar appears in the right place with spot-on laborde coords and correct lat longs....so..the mystery is...why is mapinfo not able to replicate the laborde projection?  having fiddled (at random)  with the false eastings/northings  i have not been able to get a unifying parameter to re-scale the values to compensate for any simple 'metric-imperial units'  type errors (thanks Sam)..in other words the E and N need differing factors for MI to get madagascar to 'locate' properly in the world.. curious and a little annoying  (its also the first time Mapinfo has seriously stumped me in nearly 12 years...)

regards

 

r

 



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