GDA2020 Basemaps

[KylieMiddleton]

@GordonSumerling 

The Esri Tech blog on GDA2020 https://esriaustraliatechblog.wordpress.com/2018/12/24/understanding-gda2020-and-its-relationship-wi... recommends>

1. Transform all data to GDA2020 and republish to Web GIS in GDA2020 or a GDA2020-based projected coordinate system.
2. When publishing to WGS84, utilise the projection path GDA2020⇒GDA94⇒ Data will be published with GDA94 accuracy and coordinate transformations between WGS84 and GDA94 can be Performed.
3. Create your own basemaps (Imagery, Street and Topographic) in GDA2020
4. DO NOT mix data from GDA94 and GDA2020 in Web GIS as there will be a 1.8 metre alignment error regardless
5. If coordinate conversion is required in Web GIS from WGS84 to GDA2020 then a transformation path of WGS84⇒GDA94⇒GDA2020 should be utilised

On point 3. Create your own basemaps in GDA2020 - has anybody done this and also successfully published as a WMTS? Is this even possible as default cache method is WGS84? Is this recommendation implying using the method GDA2020>WGS84 using null projection (EPSG:8450). As a side note customers using Geocortex require services to be published in the same datum as their basemap datums so the getcaps would need to specify GDA2020. 

P.S a dedicated GDA2020 section in communities would be great 🙂 Kylie

[Anonymous User · Accepted solution]

Hi Kylie,

While, I have not come across that workflow before, I can address some of the points that you raised. You are correct in that by default, tile caches use the Web Mercator/WGS84 projection. If you would like to cache your data using a different projection, you will have to use the Generate Tile cache Tiling Scheme geoprocessing tool. this allows you to specify scales and coordinate system, among other parameters

https://pro.arcgis.com/en/pro-app/tool-reference/data-management/generate-tile-cache-tiling-scheme.h...

Then, when caching your service, import the XML file that was created from running the tool, and the cache will be built according to your specifications.

Hope this helps!

-Calvin

[KylieMiddleton]

So you would need to use ArcGIS Pro then? We are not currently using Pro to publish our data as it's not integrated into our architecture yet.

[Anonymous User]

Hi Kylie,

The same tool also exists in ArcGIS Desktop.

https://desktop.arcgis.com/en/arcmap/latest/tools/data-management-toolbox/generate-tile-cache-tiling...

Here is a technical article outlining this workflow:

https://support.esri.com/en/technical-article/000012213

Best,

Calvin

[GordonSumerling · Accepted solution]

Hello Kylie,

Creating your own basemap in GDA2020 (Projected or geographical) will mean that you need to 

1) Define your own tiling scheme for that basemap. Yes this is different to the global basemaps as they are all in WGS84 Web Mercator Auxiliary Sphere. The traditional tiling scheme for the global basemaps is defined if you choose the ArcGIS Online tiling scheme.  (Generate Tile Cache Tiling Scheme)

2) Use this tiling scheme as the definition for your basemaps. (Manage Tile Cache). 

      NOTE: I would consider using Vector Tile Packages as they are more efficient and faster to create and update.

3) Package the tile cache for loading to ArcGIS Online or ArcGIS Enterprise by using the Export Tile cache tool

4) Once you have this basemap package then you publish to ArcGIS Online or ArcGIS Enterprise using the Share tools

5) You can use this as you basemap but everything you place on-top of it now will be projected to GDA2020. You cannot add other global basemaps behind as they are in WGS84 Web Mercator Auxiliary Sphere but the map will be in GDA2020. 

6) From this you should be able to add the WMS capability (Which includes the WMTS for cached basemaps).

Also good suggestion on the GeoNet for creating a GDA2020 discussion group I will look into this

Cheers

Gordon

[KylieMiddleton]

Thanks Gordon and Travis for your very helpful responses! Cheers Kylie

[GordonSumerling]

NOTE: in January 2021 ICSM released new transformations that support GDA2020 to WGS84 and Esri released ArcGIS Pro 2.8 in May 2021 which supports these. Please refer the following article for these updates  New GDA2020 transformations for WebGIS

[PeterMacKenzie2]

@GordonSumerling - would ESRI or ESRI Australia ever create  vector tiles in GDA2020 of some of the core basemaps (such as ESRI Topographic) and host them for all of us to use? Has that been proposed before?
Perhaps not because of the null transformation between GDA94 / WGS84  but now we're going to using GDA2020 basemaps and avoiding WGS84 like the plague,it seems inefficient to all create our own vector tiles of "ESRI's" basemaps  and continually update them. Steer me back if I've got this concept wrong here. 

[GordonSumerling]

@PeterMacKenzie2 We are investigating this as part of the whole GDA2020 data migration. Currently the Esri basemaps are classified as WGS84 ensemble which does not define level of accurcay. However it is understood that the GDA94 data is directly translated to WGS84 with a NULL transformation. There is a discusion happing to re-align these with the GDA2020 position. This though is a significant piece of work and needs public notification.