ArcGIS Server and GDA2020


Background

Esri has been working for to incorporate time-based geographic transformations into the software. As you can imagine, these transformations are hugely complex, since the process involves the actual position of the features on the surface of the earth, taking continental drift, and plate tectonic motion into consideration. These time-based transformations are based on a so-called “epoch”, which is the date on which all features are at located in relation to an absolute location.

There are several moving parts involved here.

1] The computer programming to perform the math to implement these geographic transformations.

2] The transformation parameters (14 for time based transformations) to transform data between an original, static datum like GDA94, which assumes that the features of the earth are in one position and not moving and a datum like GDA2020.  Later datums will be dynamic so as to take  plate motion into consideration, this is discussed here, software vendors are already planning for this new approach.

3] The transformation parameters to transform between one time-based datum, and another more current time-based transformation – GDA2020 to say, GDA2030 for example if such a thing were to exist someday.

What the ArcGIS Software does not do is calculate these transformation parameters. ArcGIS checks them and verifies that the transformation parameters provided by the national government agency perform to the accuracy provided, but does not calculate them.

Therefore, even if ArcGIS has the transformation method in place to perform a 14-parameter time-based transformation, ArcGIS needs the transformation parameters, from the national government agency that has created the specific transformation for their area of interest.

ArcGIS software does support GDA2020 Z point transformations ‘out of the box’ but not the NTv2 grid files for the mathematical and mathematical plus distortion transformations.  The NTv2 grid files will have to downloaded (which include some content from Geoscience Australia) for the appropriate ArcGIS version from;

 My Esri > Product Components > Data and Content > ArcGIS Coordinate Systems Data

Description:
Contains the data files required for the … transformation method and vertical transformation files for … the world … for use with either ArcMap, ArcGIS Enterprise, ArcGIS Engine, or an ArcGIS Pro per machine install

and install on each ArcGIS machine, this will install to C:\Program Files (x86)\ArcGIS\CoordinateSystemsData.

This installer is specific to the ArcGIS version, eg:

  • ArcGIS_Coordinate_Systems_Data_Windows_1061_163829.exe
  • ArcGIS_Coordinate_Systems_Data_Windows_1071_169282.exe

The NTv2 transformation between GDA 1994 and GDA 2020 is one small moving part of this major upheaval in the world of geodesy, and the pursuit of ever-more-accurate and ever-more-precise coordinates for features on the earth’s surface.
Esri publish documentation specific to each ArcGIS version which have included GDA2020 for some time, for instance in 10.5.1 they put the transformation GDA_1994_to_GDA_2020_NTv2_CD in 10.5.1 assuming that they knew the names of ntv2 files, then Geoscience Australia changed the file names so this transformation was deprecated in the _C versions. As far as this naming is concerned _C is for Conformal and _CD is Conformal_and_Distortion. Each of these transformations will get a unique Well Known ID (WKID) value each time the transformation changes. For example:

geographic_transformations_1060

geotran_1071_24

How To: Select the correct geographic (datum) transformation when projecting between datums

Esri Australia have been publishing blogs on GDA2020 for a while;

https://esriaustraliatechblog.wordpress.com/tag/gda2020/

Up to version 10.6.1 for some situations you needed to rename the GSB file as mentioned here;

https://esriaustraliatechblog.wordpress.com/2018/01/04/gda2020-arcgis/

The transformation 108065 was added to the Projection Engine at 10.6.0, but was removed from 10.6.1, so that transformation never existed at 10.6.1. The same transformation, but with a new name for the GSB file was added again at 10.7.1.
The conclusion here is that you should upgrade to the latest version of ArcGIS to get the most GDA2020 transformations.
A map of the approximate shifts from GDA94 to GDA2020 locations across Australia is here; https://www.icsm.gov.au/gda2020

ArcGIS Server (does not support time-dependent transformations yet)

Expect in 2020 many agencies will be publishing services natively GDA2020.
If all data is stored in GDA2020 and published in GDA2020 there should not be any issues, apart from later on taking into account the epoch of the data, as mentioned here;

https://esriaustraliatechblog.wordpress.com/2018/12/24/understanding-gda2020-and-its-relationship-with-web-gis/

If you are upgrading your servers and need to change the coordinate systems of your data or services, please republish the services. The version of the ArcGIS Coordinate Systems Data should be identical on the desktop client and server should be the same.

You can test a server’s support for a particular transformation if the GeometryServer is running;

https://localhost/server/rest/services/Utilities/Geometry/GeometryServer/project?inSR=4283&outSR=7856&geometries={“geometryType” : “esriGeometryPoint”,”geometries”: [{“x”: 153.30141143,”y”: -27.90831298}]}&transformation=108447&transformForward=true&vertical=false&f=html

should return (which is less than 1mm away from the expected ordinates);

{“geometries”: [{ “x”: 529661.2445906086, “y”: 6912919.071889246}]}

For instance, trying;

url1will return the message;

Invalid or missing input parameters.
the specified wkid or wkt is not a geotransformation

As;

url2

is at ArcGIS version 10.4.1 so is not capable of doing GDA2020 transformations.

 

 

 

 
If you access a more recent ArcGIS Server version like;

url4

 

and you get an error like;

Unable to complete operation.
Cannot load the data file Dataset_australia/GDA94_GDA2020_conformal_and_distortion for the geographic transformation GDA_1994_To_GDA2020_NTv2_2_Conformal_and_Distortion.

Then the server is capable of that transformation but the ArcGIS Coordinate Systems Data installer has not been run on the server.
What this means is that if you query the following to add a layer to a web map of yours which is going to be in a particular coordinate system like outSR=7856 https://epsg.io/7856 and you get geometry from this layer;

 

url5

{“displayFieldName”:”PROP.QLD_SURVEYCONTROL_SCDB.MRK_ID”,”fieldAliases”:{“PROP.QLD_SURVEYCONTROL_SCDB.GDALATITUDE”:”GDA latitude”,”PROP.QLD_SURVEYCONTROL_SCDB.GDALONGITUDE”:”GDA longitude”,”PROP.QLD_SURVEYCONTROL_SCDB.AHDHEIGHT”:”AHD height”},”geometryType”:”esriGeometryPoint”,”spatialReference”:{“wkid”:7856,”latestWkid”:7856},”fields”:[{“name”:”PROP.QLD_SURVEYCONTROL_SCDB.GDALATITUDE”,”type”:”esriFieldTypeDouble”,”alias”:”GDA latitude”},{“name”:”PROP.QLD_SURVEYCONTROL_SCDB.GDALONGITUDE”,”type”:”esriFieldTypeDouble”,”alias”:”GDA longitude”},{“name”:”PROP.QLD_SURVEYCONTROL_SCDB.AHDHEIGHT”,”type”:”esriFieldTypeDouble”,”alias”:”AHD height”}],”features”:[{“attributes”:{“PROP.QLD_SURVEYCONTROL_SCDB.GDALATITUDE”:-27.9083129838,”PROP.QLD_SURVEYCONTROL_SCDB.GDALONGITUDE”:153.3014114276,”PROP.QLD_SURVEYCONTROL_SCDB.AHDHEIGHT”:30.34},”geometry”:{“x”:529660.65561161563,”y”:6912917.6855818881}}]}

Or this (where you also asked for the datum transformation);

url6

{“displayFieldName”:”PROP.QLD_SURVEYCONTROL_SCDB.MRK_ID”,”fieldAliases”:{“PROP.QLD_SURVEYCONTROL_SCDB.GDALATITUDE”:”GDA latitude”,”PROP.QLD_SURVEYCONTROL_SCDB.GDALONGITUDE”:”GDA longitude”,”PROP.QLD_SURVEYCONTROL_SCDB.AHDHEIGHT”:”AHD height”},”geometryType”:”esriGeometryPoint”,”spatialReference”:{“wkid”:7856,”latestWkid”:7856},”fields”:[{“name”:”PROP.QLD_SURVEYCONTROL_SCDB.GDALATITUDE”,”type”:”esriFieldTypeDouble”,”alias”:”GDA latitude”},{“name”:”PROP.QLD_SURVEYCONTROL_SCDB.GDALONGITUDE”,”type”:”esriFieldTypeDouble”,”alias”:”GDA longitude”},{“name”:”PROP.QLD_SURVEYCONTROL_SCDB.AHDHEIGHT”,”type”:”esriFieldTypeDouble”,”alias”:”AHD height”}],”features”:[{“attributes”:{“PROP.QLD_SURVEYCONTROL_SCDB.GDALATITUDE”:-27.9083129838,”PROP.QLD_SURVEYCONTROL_SCDB.GDALONGITUDE”:153.3014114276,”PROP.QLD_SURVEYCONTROL_SCDB.AHDHEIGHT”:30.34},”geometry”:{“x”:529660.65561161563,”y”:6912917.6855818881}}]}

Then you are not going to see the points transformed onto your map as you expect (as the server does not have the NTv2 files) and the layer will be not shifted as needed.

Make it your 2020 resolution to bring your ArcGIS Servers up to date, install ArcGIS Coordinate Systems Data and discuss GDA2020 with your users!

 

 

 

 

1 thought on “ArcGIS Server and GDA2020

  1. Will B Post author

    I have made some changes to the article as suggested by Joel Haasdyk to make it clear that ArcGIS Server does not support time-dependent transformations yet, however when all the standards are in place Esri will be adding this functionality to the latest ArcGIS version. ArcGIS Server 10.8 will be available within about a week, if I notice anything has changed regarding GDA2020 I will update this blog, maybe even adding a table with rows by version to make it clearer as to what interventions are required for GDA2020 support. The pdf files that I included earlier via the screen copies (that provide the all important WKID values specific to some ArcGIS versions) are only available on request from support@esriaustralia.com.au. Thanks for taking the time to read this article.

    Reply

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