Hi,

I tried the following.

1. Create Point with grid coordinates with Creator
2. Define refsys for this point with CoordinateSystemSetter to EPSG:23031m which is ED50 UTM31N.
3. Then, with ArcGIS, create a Shapefile and define refsys to EPSG:32632 which is WGS84 UTM32N.
4. Write directly from CoordinateSystemSetter to the Shapefile
5. Inspect the new Shapefile and clearly XY values are changed

Must conclude that FME "picks up" some transformation method and parameters.

I can see in Your case there is listed just one set of parameters and method for the transformation. In the ED50 <-> WGS84 case I tested there is a number of possible transformation methods and parameters. In my opinion one should therefore explicit specify the transformation in a Workspace.

Yes, if the datum changes in a reprojection, then FME must apply a method (parameters or a grid) to convert the data. That dialog just shows the list of transformation. If you go to Tools > FME Options > Coordinate Systems then you can look up a certain transformation (say AGD84 to GDA94) and - if there are grids available - edit the default options. Sometimes (like NAD27 to NAD83) there are different options that you can choose as the default by moving it up in the list.

I don't think HK1980 has a grid, so there is no option to change the order.

Thanks @mark2atsafe for clarifying I will stick to explicit define my transformations. With "all" the available methods (EsriReprojector, Reprojector, CsmapReprojector, GransReprojector..) and its associated parameters I would now rely upon understanding the "default settings" (my limitations ..)

\\Thanks for your reply.

\\Do you know whether under the geographic transformation gallery, the names of SRC_DRM and TRG_DTM must meet with the datum name that available in the datum of coordinate system gallery such that the transformation can be performed automatically ?

\\On the other hand, if the names of SRC_DRM and TRG_DTM are not available in the default coordinate system gallery, then I need to create it by myself , please correct me if I am wrong ?

\\ Is there any naming rules of the datum names?

/Thanks for your reply.

/ I also try the coordinate transformation in ArcMap using the create custom transformation tool and same result is found as FME. It can conclude that FME do make the transformation automatically but it seems that the datum names from the SRC_DRM and TRG_DTM must meet with that available in the default coordinate system gallery. Otherwise, it has to be created manually.

In answer to your questions, yes the datum names in the Geographic Transformation Gallery must match a datum already available in FME.

If the datum is not already available in FME, then yes, you could create it by yourself. Our Help documents tell you how to create a new datum.

Yes, there are naming rules:

• must be no more than 23 characters
• first character must be alphanumeric or ':' (cs_Unique)
• must not include special characters other than those in this set: ' _-$:.;~/'
• must contain at least one alphabetic character
• must not contain two consecutive spaces
• if the first character is numeric, the first non-numeric character must be alphabetic or an underscore
• case is preserved for display, but is not considered significant (yet for historical reasons, names defined in this file are ALWAYS case sensitive)

I would also try to use plain Ascii characters (no accents) and not use anything that might already exist or be a reserved word.

If you create a datum that doesn't have an appropriate entry in the Transformation Gallery, then I am not sure what happens when you carry out that translation. I have asked our developers for that information. But you can create a custom transformation, and that too is in our Help documents.

I'm told that if you create a datum that doesn't have an appropriate entry in the Transformation Gallery, then any reprojection will be attempted through WGS84 using the transformation defined in the datum.