Geographic coordinate change

Question

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)

To

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.

Answer 1

Esri has that transformation definition, which is EPSG:1272. I believe that your input data's projected coordinate reference system includes a geographic coordinate reference system with one or more names that don't match how it's defined in the Esri software.

If you look at the definition you posted, here are the first two lines:

GGRS87_Greek_Grid

Authority: Custom

Note that the Authority is listed as Custom. If ArcGIS recognized the definition, it would list 2100 here instead.

Use the Define Projection Tool to redefine the input data's coordinate system. When using the tool, type in 2100 to find the GGRS87 Greek Grid definition. Once the definition is updated, you should be able to use the Project Tool to convert to EPSG:3857.

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Another solution if you don't want to change the original data's coordinate reference system, you can use the Create Custom Geographic Transformation tool, but you must select the geographic coordinate reference system from the data, rather than Esri's definition of GGRS87.