Coordinate system conversion

[RonMan]

I am a beginner at ArcGIS and i do have a question related to coordinate system conversion.

I just need to convert coordinates from WGS84 UTM 37S to ARC 1960? I know that is horizontal conversion.  My question is do i still have to do vertical datum transformation though i am concerned with equivalent horizontal coordinates?  Another thing is i would do the WGS84 37S to ARC 1960 projection in Arcmap 10.3.  But the vertical transformation in Geographic Calculator software.  Is that correct?

Thank you in advance.

Regards,

Ron

(U.A.E.)

[RonMan]

Also i checked the reprojected value against other software which can transform like Civil 3D/Map and Bentley Microstation.  They have separate values but close enough around 10m to 20m. Is that expected to get different answers?

Thanks.

Regards,

Ron

[DanPatterson_Retired]

If you have a transformation available use it in all circumstances to avoid the differences.  Check other software to see if they offer the same capabilities

[MelitaKennedy]

If you're in ArcGIS Desktop, yes. In Desktop, transformations came in a release or two later than the first release and at that point, we had never set a particular "default" transformation for any pair of GCS. ArcGIS Pro does set a transformation by default but it's using the data extents to try to set a reasonable transformation, rather than the most generic one (generic AKA the one that covers the most area and usually has the worst accuracy).

Those values are big enough that I would suspect that they're using a different or no transformation.

[RonMan]

Thanks Melita and Dan.

Regards,

Ron

[NeilAyres]

My 2c about all this stuff surrounding datum transformations.

In general, I advise users to leave the data as it came and let ArcMap do the transformation on-the-fly. The reason for this is that at least you can see, by checking the transformation button in the df properties, what exactly is going on, ie which transformation is being used for whatever datum pair. This also means that if a new transformation becomes available, you can take advantage of it, if it provides a more "accurate" answer.

If new data is created using either the project tool or an export from the df with a transformation set, once created, the knowledge of quite how that data has been transformed (which exact transformation and its parameters) is lost. You never know how it got to be where it is now.

This has always been a problem with the documentation of data.

[RonMan]

Thanks Neil for your advice.

[MelitaKennedy]

Neil, 

It's true that an export from the data frame won't record what transformation was used, but geoprocessing tools do record that information in the history, and I think somewhere in the data's metadata, but yes, it's hard to get at.

Melita

[NeilAyres]

Melita,

if you can let me know where this info is stored in the metadata, that would be great.

I have never managed to find it.

Thanks,

Neil

[MelitaKennedy]

I haven't tried this: Viewing tool execution history—Help | ArcGIS Desktop 

[RonMan]

Thanks for the viewing tool Melita.

It would be good if the transformation history can be  found, EDIT:> viewing tool seems to be the way.  Thanks Melita

I did a quick search through the files generated by the project tool using notepad++, i didn't find any record showing the history.

I think either have the filename contain the transformation or have a record of every transformation tasks.