Matt Morris

Orthometric Heights with Trimble GNSS & Esri Collector (Part 1 of 4)

Blog Post created by Matt Morris on Apr 3, 2020

Trimble Mobile Manager with Esri Collector for ArcGIS


We are very pleased to release version 2.3 of Trimble Mobile Manager (TMM). As this post details, there are new areas of functionality which will be of particular benefit to users of Esri Collector for ArcGIS version 20.1.0 or above, released this week. At version 2.2 of TMM, we expanded functionality beyond Catalyst to serve as the primary configuration utility for integrated and Bluetooth receivers including the Trimble TDC-series, Trimble R-series, and Spectra Geospatial SP-series. In this version, we have added support for in-field orthometric height calculation and have made the advanced geodetic functionality available to Esri Collector for ArcGIS. These new features are also available to other partner apps supporting connections to Trimble and Spectra Precision GNSS receivers using the Trimble Precision Software Development Kit (TPSDK) or location sharing (mock location) workflows, but in this blog post, we are focusing on describing the interaction between TMM and Collector for ArcGIS, and how to make use of these features in that workflow.


Summary of new features

There are two new areas of functionality in TMM for the Esri Collector user: orthometric (MSL) heights and advanced geodetics.

Orthometric Heights

Previously, all heights (Z coordinate values) provided by Trimble receivers into Esri Collector were in terms of height above ellipsoid (HAE). This HAE value would be displayed in the GPS Details screen and also used in both GNSS metadata (ESRIGNSS_ALTITUDE) and the 3D feature geometry, now fully supported in Esri Collector.


In TMM 2.3, the GNSS Configuration area has been expanded to include the specification of a geoid for the purposes of calculating an orthometric height (typically, above mean sea level or MSL) from the HAE value. The user can select from a curated list of global and local geoids or can side-load their own geoid grid file (GGF). By default, the global EGM96 geoid is used. This ensures that Esri Collector will always receive both an HAE value and an MSL value. This applies to both the native receiver connection workflow and the location sharing (mock location) workflow. Esri Collector will use the HAE value in the GNSS metadata and the MSL value in the 3D feature geometry. Further, this information is available directly in the field (via Arcade expression in the popup configuration) without the need for post-processing (see Parts 2 and 3 in the series).

For more information on orthometric heights and related topics, please see the Elevation Concepts for GIS blog post.


Note: As a reminder, when using Trimble receivers in this new version of Esri Collector, the antenna height you store in Esri Collector should not be manually adjusted to reflect the antenna phase center (APC) or reference point (ARP) offset value, simply use the height of the range pole from the bottom of the receiver to the ground. Collector will automatically include the correct APC value in the height calculation based on the model of Trimble (or Spectra Precision) receiver that you are connected to.

Illustration of measuring antenna height from base of receive to the ground

Advanced Geodetics

As part of configuring the real-time correction source, TMM gives the user the ability to set the source (incoming) and output reference frames (also referred to as datums in this context). For example, the user could indicate that their VRS network is using NAD83 (2011) coordinates but that they want ITRF2014 coordinates passed into the data collection application. Or, they are using Trimble RTX corrections in an ITRF2014 frame and want NAD83 (2011) coordinates passed into the data collection application. The datums can be selected manually or automatically (based on location). If the two datums are different, then one or more datum transformations will be performed between the incoming GNSS positions from the receiver and the outgoing GNSS positions to the data collection application. TMM will generally use 14-parameter time-dependent methods for the most accurate global to local (or vice-versa) datum transformations.

In TMM 2.3, this explicit control of source and output GNSS datums applies to the Esri Collector workflow as well. All settings from the GNSS Configuration area of TMM are used when Esri Collector connects natively to one of the supported Trimble receivers. Additionally, users can specify a particular epoch for the incoming GNSS source reference frame instead of the default, reference epoch. This is useful in tectonically active areas where a real-time network provider may regularly update their reference frame within the same realization of a datum. For example, in California, most real-time networks use a 2017.50 or even 2020.00 epoch of NAD83 (2011). This can now be specified as part of the configuration in TMM such that coordinates get adjusted to the reference epoch of a datum (e.g., in this example, NAD83 (2011) epoch 2010.00) for use in Esri Collector or a different data collection application.


How to get it

Trimble Mobile Manager v2.3.0 and Esri Collector for ArcGIS v20.1.0 are both available for download from the Google Play Store today.


Continue to Part 2: Configuration in the Office...