I try to make a coordinate converter using Proj4JS for mobile app, I use this source code. Before I tested conversion for WGS84 geographic and WGS84 UTM, there was not problem with it. I tested conversion from TUREF TM zone:27 to ED50 TM zone:27 that input coordinates are Easting:507768.06 Northing:4354677.64. For proj4js output is; Easting:507819.315 Northing:4354847.596 But when I tested it for epsg.io or pyproj output was Easting:507815.93 Northing:4354857.26.

Edit: I use proj4 text parameters for pyproj and proj4js.

TUREF / TM27: +proj=tmerc +lat_0=0 +lon_0=27 +k=1 +x_0=500000 +y_0=0 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs 
ED50 / TM27: +proj=tmerc +lat_0=0 +lon_0=27 +k=1 +x_0=500000 +y_0=0 +ellps=intl +towgs84=-87,-98,-121,0,0,0,0 +units=m +no_defs 

What am I missing?

1 Answer 1


I used proj4.js file. After replacing it with proj4-src.js it transforms properly right now. I will continue testing.

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