topic Re: Coordinate system conversion in Coordinate Reference Systems Questions

Coordinate system conversion

RonMan — Sun, 28 Jan 2018 04:58:33 GMT

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.)

Re: Coordinate system conversion

DanPatterson_Retired — Sun, 28 Jan 2018 09:12:40 GMT

You need to do a projection using the Project tool

A list of vertical transformations that are supported can be found in the Geographic datum transformation link. (Equivalent documentation exists for 10.3)

Re: Coordinate system conversion

RonMan — Sun, 28 Jan 2018 10:53:34 GMT

Thank you Dan for your response. I appreciate it and thanks for the link of

"ArcGIS 10.6.0 and ArcGIS Pro 2.1 Geographic and Vertical Transformation Tables"

So is there a need for a vertical transformation?

As a beginner i am swamped with the long list. Could you be able to explain further how the table will be used in my transformation task?

Thank you.

Regards,

Ron

Re: Coordinate system conversion

DanPatterson_Retired — Sun, 28 Jan 2018 13:17:27 GMT

If your concern is with the horizontal, then there should be no need. The various horizontal transformations are provided in the link that I sent. At the bottom of the page is a link to a pdf which shows those that are directly supported. If you were offered a horizontal transformation transformation then you could it

Re: Coordinate system conversion

RonMan — Sun, 28 Jan 2018 16:51:28 GMT

Thank you for your help Dan.

Regards,

Ron

Re: Coordinate system conversion

DanPatterson_Retired — Sun, 28 Jan 2018 17:00:31 GMT

No problem Ron, hope it all works out

Re: Coordinate system conversion

RonMan — Tue, 30 Jan 2018 18:05:31 GMT

I have a follow up question regarding this coordinate transformation.

I made a simple test.

I made one sample point in a shapefile with CS of WGS84 37S and imported it in ArcMap.

I set the dataframe's CS to Arc 1960 37S and calculated the point's X and Y into additioanal fields in the attribute table using geometry calculator and using dataframe's CS.

The value i a getting from the above is different from the value i get when i use project tool.

I am expecting they should be the same values. I did one excercise 2 months back and arrived at the same value.

Is there any known discrepancies between the two methods? I know that i should trust the project tool more.

Thanks in advance.

Regards,

Ron

(U.A.E.)

Re: Coordinate system conversion

DanPatterson_Retired — Tue, 30 Jan 2018 18:18:20 GMT

How different? If they are in the order of 10s or 100s or meters, then a datum shift is not being applied. If none was offered, then the 60's one may not exist within arcmap.

I will flag MKennedy-esristaff‌ (just another easy one Melita )

Re: Coordinate system conversion

RonMan — Tue, 30 Jan 2018 18:23:46 GMT

Thanks Dan for your quick reply.

I could give the exact numbers tomorrow.

Regards,

Ron

Re: Coordinate system conversion

MelitaKennedy — Tue, 30 Jan 2018 18:58:01 GMT

Did you use the Calculate Geometry option on the fields? Was it set to use the data frame's coordinate system? If so, did you set the transformation in ArcMap? If not, open data frame properties, select the coordinate systems tab and click the Transformations button.

If the data frame is Arc 1960, in the top box, select WGS 1984. Click the pull-down at the bottom and select the same transformation that you used in the Project Tool.

Re: Coordinate system conversion

RonMan — Wed, 31 Jan 2018 05:54:58 GMT

Thank you Melita for your response.

So it is the transformation button i am missing. I got now the same value with the project tool. Thanks.

Do I have to set it everytime i calculate geometry using dataframe's coordinate system?

I was thinking that reprojection is 'on the fly' so i do not have to set any transformation using the calculate geometry method.

Regards,

Ron

Re: Coordinate system conversion

RonMan — Wed, 31 Jan 2018 06:00:45 GMT

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

Re: Coordinate system conversion

DanPatterson_Retired — Wed, 31 Jan 2018 10:24:42 GMT

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

Re: Coordinate system conversion

MelitaKennedy — Thu, 01 Feb 2018 23:47:04 GMT

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.

Re: Coordinate system conversion

RonMan — Fri, 02 Feb 2018 07:49:30 GMT

Thanks Melita and Dan.

Regards,

Ron

Re: Coordinate system conversion

NeilAyres — Mon, 05 Feb 2018 14:13:53 GMT

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.

Re: Coordinate system conversion

RonMan — Mon, 05 Feb 2018 17:01:28 GMT

Thanks Neil for your advice.

Re: Coordinate system conversion

MelitaKennedy — Mon, 05 Feb 2018 21:35:33 GMT

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

Re: Coordinate system conversion

NeilAyres — Wed, 07 Feb 2018 08:02:07 GMT

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

Re: Coordinate system conversion

MelitaKennedy — Wed, 07 Feb 2018 19:14:03 GMT

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