topic Re: Transformation from GRS_1980 to OGSB_1936 in Coordinate Reference Systems Questions

Transformation from GRS_1980 to OGSB_1936

MS10 — Wed, 04 May 2016 12:21:49 GMT

Hi, I'm attempting a transformation between these two coordinate systems. I've tried by adding the GRS_1980 raster then selecting Transformations > Using, however the only option is <custom> New Geographic Transformation. I used this method then tried to clip the GRS_1980 raster to the OGSB_1936 however I dont think it has worked correctly as the GRS raster doesnt align and overlay properly with the OGSB raster. Anyone have any advice, some details on the datasets below.

GRS_1980:

Spatial coverage: Europe

Pixel size: 500m

OGSB_1936:

Digital Elevation Model of area in southern England

Pixel size:50

Re: Transformation from GRS_1980 to OGSB_1936

AdrianWelsh — Wed, 04 May 2016 12:50:19 GMT

Hi, are you using ArcMap? Which version? In any case, I am tagging Melita Kennedy on this to hopefully give you a good answer!

Re: Transformation from GRS_1980 to OGSB_1936

MS10 — Wed, 04 May 2016 12:55:08 GMT

Hi, yes I'm using ArcMap 10.3.1. Thanks

Re: Transformation from GRS_1980 to OGSB_1936

DanPatterson_Retired — Wed, 04 May 2016 13:05:02 GMT

You are using the Project Raster—Help | ArcGIS for Desktop tool, I presume. As the help topic suggests there is a transformation document (geographic_transformations.pdf) in you install directory ... C:\Program Files (x86)\ArcGIS\Desktop10.4\Documentation ... in my case 10.4 ... where you can find the transformation parameters if they haven't been implemented specifically

Re: Transformation from GRS_1980 to OGSB_1936

MS10 — Wed, 04 May 2016 13:10:26 GMT

Hi Dan, I wasn't using that tool initially, I attempted it through the 'Geographic Coordinate Systems Warning' that opened when i added the layer. I will try what you suggested. Thanks

Re: Transformation from GRS_1980 to OGSB_1936

MS10 — Wed, 04 May 2016 13:48:40 GMT

Can't seem to find any mention of a GRS_1980_IUGG to OGSB_1936 transformation in the .pdf.

Re: Transformation from GRS_1980 to OGSB_1936

DanPatterson_Retired — Wed, 04 May 2016 13:52:49 GMT

there may not be a transformation create, but you can at least compare the spheroids used to see if there are any matches...given that the latter one seems to be old

Re: Transformation from GRS_1980 to OGSB_1936

MS10 — Wed, 04 May 2016 15:29:18 GMT

The OSGB spheroid is Airy 1980 (EPSG 7001), not sure of the spheroid for the GRS_1980. The pdf doesnt contain mentions of spheroids used in the transformations either.

Re: Transformation from GRS_1980 to OGSB_1936

DanPatterson_Retired — Wed, 04 May 2016 15:58:27 GMT

The Digital National Framework for OSGB

But I will have to toss you off to Ordnance Survey National Grid - Wikipedia, the free encyclopedia

until Melita Kennedy shows up

Re: Transformation from GRS_1980 to OGSB_1936

MelitaKennedy — Thu, 05 May 2016 18:39:18 GMT

I would expect that the European data is on ETRS89 which uses GRS80. Can you redefine the (Define Projection or in "catalog") the geographic coordinate system for the raster to ETRS 1989? Then you should starting seeing OSGB_1936_To_ETRS_1989_1 as a possible transformation. It's file-based and will only affect data in the UK.

Edit: If you don't see that transformation, you might be on an earlier version that didn't have the grid file. Please post what software version you're using.

Melita

Re: Transformation from GRS_1980 to OGSB_1936

MS10 — Fri, 06 May 2016 10:12:15 GMT

Hi thanks for the reply, I redfined the raster to ETRS 1989 (Data Management > Define Projection), I then tried Project Raster using the following:

Output coordinate system: OSGB 1936

Geographic transformation: OSGB_1936_To_ETRS_1989_1

However i get the error

"ERROR 999999: Error executing function.

General function failure [Rf_ProjectRaster]

The operation was attempted on an empty geometry.

Failed to execute (ProjectRaster)."

Im using ArcMap 10.3.1, the raster also dissappears once i've defined the projection as ETRS 1989. Just to clarify the raster Spatial Reference is defined as GRS_1980_IUGG_1980_Lambert_Azimuthal_Equal_Area.

Thanks.

Re: Transformation from GRS_1980 to OGSB_1936

MelitaKennedy — Sat, 07 May 2016 19:22:13 GMT

Ack, sorry about that. When you redefined the spatial reference/coordinate system, you should change only the geographic coordinate system portion. Keep the Lambert azimuthal definition as it is.

Melita

Re: Transformation from GRS_1980 to OGSB_1936

MS10 — Sun, 08 May 2016 20:43:03 GMT

Sorry i'm not following there, what should I do differently? Thanks

Re: Transformation from GRS_1980 to OGSB_1936

NeilAyres — Mon, 09 May 2016 06:52:57 GMT

What Melita is saying that that you should have only changed the underlying GCS of your existing coordinate system,

scoot down using the arrow to the bottom half of the edit window. (picture 2 below).

Re: Transformation from GRS_1980 to OGSB_1936

MelitaKennedy — Mon, 09 May 2016 19:30:35 GMT

When you go to edit the coordinate system (spatial reference), on the bottom half of the projected coordinate system dialog, you can click the Change button to edit just the geographic coordinate system.

Re: Transformation from GRS_1980 to OGSB_1936

MS10 — Wed, 11 May 2016 09:47:38 GMT

Hi, I changed the Geographic Coordinate System to ETRS 1989 using this dialog, however i'm still getting the same error when I use Project Raster.

Re: Transformation from GRS_1980 to OGSB_1936

NeilAyres — Wed, 11 May 2016 15:05:09 GMT

What was the coordinate system for your original GRS80 based data?

If you messed it up before reset it back to the original (or get the data again).

Then in Catalog, look at the coordinate system tab on the properties page.

There you should be able to modify this coordinate system. But only change the GCS part.

From GRS 80 to WGS84. Then and only then will you have a transformation available between OGSB and WGS when you do the project.

Re: Transformation from GRS_1980 to OGSB_1936

NeilAyres — Wed, 11 May 2016 15:06:10 GMT

And, how closely are you expecting these 2 datasets to align anyway. The one has 500m pixels the other 50m...???

Re: Transformation from GRS_1980 to OGSB_1936

MS10 — Wed, 11 May 2016 20:57:54 GMT

This is the original data:

Following what you said Neil I changed the GCS to WGS 84 through this dialog:

Then I used Project Raster > OSGB to WGS84:

However i'm still getting this error:

Thanks for the help

Re: Transformation from GRS_1980 to OGSB_1936

NeilAyres — Thu, 12 May 2016 06:46:43 GMT

Can you show us the extent of that OSBG raster. Also on the layer properties.