I am using ArcMap 10.4 and I want to convert my layer of Athens (http://geodata.gov.gr/dataset/api0unon-o1kodou1kwv-tetpaywvwv-anuou-a0nvaiwv/resource/d2e17dd6-8e1e-4c34-9111-fb3ac1bc9da4) municipality which is in
Current coordinate system:
GGRS87_Greek_Grid Authority: Custom Projection: Transverse_Mercator false_easting: 500000,0 false_northing: 0,0 central_meridian: 24,0 scale_factor: 0,9996 latitude_of_origin: 0,0 Linear Unit: Meter (1,0)
WGS_1984_Web_Mercator_Auxiliary_Sphere WKID: 3857 Authority: EPSG Projection: Mercator_Auxiliary_Sphere False_Easting: 0,0 False_Northing: 0,0 Central_Meridian: 0,0 Standard_Parallel_1: 0,0 Auxiliary_Sphere_Type: 0,0 Linear Unit: Meter (1,0)
My goal is to make a web map and use also OpenStreetMap as a basemap.
I have tried to use the project tool but it does not have this transformation.
I have also tried to make a new transformation as described in this link https://georepository.com/transformation_1272/GGRS87-to-WGS-84-1.html
Parameter Value / File Ref Sign Reversible Unit X-axis translation -199.87 YES metreOpen Y-axis translation 74.79 YES metreOpen Z-axis translation 246.62 YES metreOpen
and still I get an error.