What values are used from the ESRI Terrain service if used as DEM in FMV Video Multiplexor?

[Anonymous User]

What values are used from the ESRI Terrain service if used as DEM in FMV Video Multiplexor?

The terrain service accepts definition queries to use specific underlying DEM datasets.

If no definition query is used, how do we know what values (and subsequently, the vertical datum) are used to report orthometric elevation?

EDIT: This question could be also be generalized to any analysis step on the Terrain layer e.g. Extract Values to Points.

[RyanDeBruyn]

@Anonymous User   If I understand your question correctly...

A terrain service could be a cached service or image service referencing to mosaic dataset depending on which endpoint you are looking at.

For the ESRI terrain service (https://www.arcgis.com/home/item.html?id=58a541efc59545e6b7137f961d7de883 )  see the notes on datasource and mosaic method. 

By default for the mosaic dataset ,  it will give you the best data available on the AOI otherwise if you can make a query to ask for SRTM/NED specifically.

[Anonymous User]

@RyanDeBruynThe documentation says that it's sorting by the "Best" field, which relates to smallest pixel size.

However, that refers to the mosaic and "display" of the data. Does that sorting also apply when the service is used for analysis, such as a geoprocessing tool?

What I'm trying to get at is it seems like there's no way to be confident about the values the Terrain service returns without using a definition query. For example, if the spatial extent of my vector data is larger (even by a single small feature!) than the extent of the underlying "Best" part of the service, then it is unclear what the results are. Does the tool apply "Best" to the features it covers, and then "Second Best" to a feature beyond its extent? Or is the entire area reduced to "Second Best" to ensure coverage?

Sometimes when I used the FMV Video Multiplexor, the tool fails due to raster input errors with the ESRI Terrain service. I think the specific tool here isn't so important. Just trying to understand what's actually happening with the data.

[RyanDeBruyn · Accepted solution]

Yes you are correct in your understanding.  By default the "best" would be the highest resolution (smallest pixel size) for your area of interest.  For an analysis tool such as CopyRaster (or Extract) the output result would be values that pertain to the best available data (sampled at the smallest resolution) for your AOI, which could be a mix of data sources if you features or extent cover a wide area.    

Did you look at the following coverage map?  The coverage and extents of various datasets comprising this service in an interactive map, see Elevation Coverage Map.

As to the error, not sure what the you are running into.  Again make sure to look at environments and that you are not running into a service request limit (the service layer is restricted to a 5,000 x 5,000 pixel limit in a single request).

If you have a particular reproducible case or details you can contact technical support or share your issue and error messages and we can go from there.

Good luck. 

[Anonymous User]

For posterity, the Summarize Elevation toolbox describes it like this.

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• The tool uses a single resolution elevation source for the input features. The highest resolution elevation source that covers the extent all of the input features will be used.

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So unless a user adds a definition query, or checks the elevation source extent and is certain their features are within, there's no additional information that the tool provides to determine the source elevation.

[RajinderNagi]

For summarize elevation, various DEM resolution supported are listed under Parameters DEM Resolution. If you are developer, here is the API help: https://developers.arcgis.com/rest/elevation/api-reference/get-started-with-elevation-services.htm

Coverage: https://developers.arcgis.com/rest/elevation/api-reference/source-data-for-elevation-analysis-tasks....