Dear list, I have been quickly through the archive but didn’t find any topic on this. I have a projection issue concerning Madagascar. Historically there is one dedicated projection called ‘Laborde’, using International 1925 ellipsoïd with others parameters. From what i know it has been approximate with an oblique mercator projection and another called hotine oblique mercator. Then, I use ArcGIS usually for my application and want slowly to move towards R and QGIS, espacially to transform point coordinates in R (spTransform). The big problem is that none of three have the same projection definition and do display large offset when projecting GPS in WGS84 to ‘Laborde’. From the projection definition, you will see below that there is some agreement (lat of origine, scale factor, false easting, false northing, azymuth) but some are completly different : longitude of origine and prime meridian etc. As I consider ArcGIS definition and transformation to be the right one (works well!), my question are: – Is the EPSG parameters up to date? – How can i tune the parameters to obtain the same coordinates that with arcGIS. – Why lonc and not lon_0 ? (lon_0 does not give anything good) I hope I m not missing something obvious. Clovis # EPSG 29700 Via R print(CRSargs(CRS(‘+init=epsg:29700’)))  ‘ +init=epsg:29700 +proj=omerc +lat_0=-18.9 +lonc=44.10000000000001 +alpha=18.9 +k=0.9995000000000001 +x_0=400000 +y_0=800000 +ellps=intl +towgs84=-189,-242,-91,0,0,0,0 +pm=paris +units=m +no_defs’ # EPSG 29700 Via GQIS +proj=omerc +lat_0=-18.9 +lonc=41.76277083000001 +alpha=18.9 +k=0.9995000000000001 +x_0=400000 +y_0=800000 +ellps=intl +towgs84=-189,-242,-91,0,0,0,0 +pm=paris +units=m +no_defs # Laborde projection in ArcGIS laborde Projection: Hotine_Oblique_Mercator_Azimuth_Center False_Easting: 400000,000000 False_Northing: 800000,000000 Scale_Factor: 0,999500 Azimuth: 18,900000 Longitude_Of_Center: 46,437229 Latitude_Of_Center: -18,900000 GCS_Tananarive_1925 Name: GCS_Tananarive_1925 Remarks: Angular Unit: Degree (0,017453292519943299) Prime Meridian: Greenwich (0,000000000000000000) Datum: D_Tananarive_1925 Spheroid: International_1924 Semimajor Axis: 6378388,000000000000000000 Semiminor Axis: 6356911,946127946500000000 Inverse Flattening: 297,000000000000000000 Source.