With the recent support for high accuracy GPS receives in the ArcGIS Collector application, we are looking to use a cm accuracy GPS receiver (EOS Arrow 200) to collect accuracy horizontal and vertical elevations. I am aware that GNSS will only allow me to collect vertical elevations within 2-4cm with an open sky, but that is enough for the application we are using it for.
My question is, how does ArcGIS Collector handle collecting elevations? I don't have a ton of knowledge about Geoids and how this comes into play with the elevation values. Does ArcGIS Collector handle the geoid data? Is there some post processing or conversion I have to do to actually have an accuracy elevation value?
Thanks for your help!
Our Arrow 200 paired with Collector stores the RTK ellipsoidal elevation value in Meters. There does not appear to be support yet right in collector to convert this to orthometric feet. In our case the values stored for elevation need to be adjusted about 116.6 feet after converting it through NGS geoid 12b https://www.ngs.noaa.gov/cgi-bin/GEOID_STUFF/geoid12B_prompt1.prl
Esri does have some tools to update your lat, long, and elevation attribute values in ArcMap automatically back in the office https://github.com/Esri/collector-tools/tree/master/CollectorUtils
Hopefully someone from the collector team can verify this approach and whether the next update of collector will include support for vertical datum transformations on the fly.
Where do you access the elevation values once you capture them? Are they stored in a field of the feature you are collecting, or are they transferred to the geometry of a z-enabled feature?
I discovered that you need to prepare your data with a set of GPS metadata fields. Depending if you're working out of ArcMap, ArcGIS Pro, or AGOL, your workflow will look different. The article below describes the process quite well.
We just release a guide on this in Eos January 2019 newsletter. The 1st paragraph below is for the New Collector (Aurora) on iOS. (For those still using Classic, you can use the Offset menu to collect ortho heights following this older guide How to Configure ArcGIS, Collector for ArcGIS, and Eos Tools Pro for Laser Offset Mapping and Orthom....)
Eos has recently introduced support for Geoid Models (Geoid12B for the US and three Canadian geoid models in the first release). You can record orthometric heights directly in the field in Collector and Survey123 (for iOS and Android only for now). The January 2019 issue of Eos Newsletter explains the workflow on how to add the Z-Value in your map. The article is titled: How to Record Orthometric Heights in Collector v18.1.0 (Aurora) with Your Eos Arrow GNSS Receiver
For Android, still on Collector Classic, there is no Z-value support yet, but you can still record the orthometric height in the ESRI_GNSS_ALTITUDE field. As long as your setup is properly made as per this guide, and Eos Tools Pro elevation is configured for "Orthometric", orthometric heights will be recorded in the above field instead of the Ellipsoidal height.
We will be adding geoid models for other countries in a near future (Australia very soon). If requiring a specific country, please do not hesitate to send your inquiry at firstname.lastname@example.org.
Hope this helps !