Project geodetics

One of the most important aspects of a data collection project is that of the coordinate systems used—of the geodatabase feature classes, of the map, and of the correction sources (both real-time and post-processed). The combination of these, the information necessary to interoperate between Trimble and Esri, and the availability of datum transformations necessary to work between different coordinate systems, will almost always determine what coordinate system will be used in the field application.

As part of Creating and managing projects, users are presented with a Project Geodetics area within project creation. Refer to the content below for a more detailed description of this area.

The Esri ArcGIS definition of the horizontal and vertical coordinate systems used by the map layers in the project. Additionally, the Esri ArcGIS definition of the horizontal coordinate system used in the map item for display.

Geodetic workflow defines the way GNSS coordinates are stored in Terraflex and Terra Office and how they are converted when required. Depending on the ArcGIS coordinate systems above, the following geodetic workflows are available:

Store all position data in TerraFlex and Terra Office in the global WGS 1984 datum and apply transformations wherever required. Best used when the datum of the correction source does not match that of the project. Transformations in the field-side of the workflow will be done with Trimble components while transformations in the office-side of the workflow will be done with Esri ArcGIS components (see next section).

Corrected positions from local sources (VRS, RTK) will be transformed between their datum (as specified) and that of the project using standard methods. Corrected positions from global sources (RTX and SBAS) will not be transformed.

Store all position data in TerraFlex and Terra Office in the supported local datum and thus minimize the number of datum transformations required in the whole workflow. Best used when all correction sources share the same datum as the project OR when using Trimble RTX.

Corrected positions from global sources (RTX and SBAS) will be transformed using the most accurate, time-dependent methods. Corrected positions from local sources (VRS, RTK) will not be transformed and as a result, only those that specify the same datum can be included with the project.

Store all position data in TerraFlex and Terra Office in the supported local datum but allow office-side transformations between the project’s local coordinate system and that of the geodatabase using Esri ArcGIS components (see next section). This option is only available for select regions where the use of related local coordinate systems is common. In some cases, the TerraFlex project in the field will also be configured with the same coordinate system as the geodatabase with only the internal storage of position data using the related local datum (for working with local correction sources).

Corrected positions from global sources (RTX and SBAS) will be transformed using the most accurate, time-dependent methods. Corrected positions from local sources (VRS, RTK) will not be transformed and as a result, only those that specify the same datum can be included with the project.

Based on the Geodetic Workflow setting and the way datums and datum transformations are modeled in Esri ArcGIS components, it may be necessary to select the following datum transformations:

  • Transformation for geodatabase (storage)

    The datum transformation(s) that will be used to transform between Terra Office and ArcGIS feature geometries at the time features are stored or retrieved to/from the ArcGIS data source. This includes both horizontal and vertical components.

  • Transformation for map (display)

    The datum transformation that will be used to display Terra Office feature geometries and positions as temporary graphic elements on the map.

The coordinate system that will be used for the project in both the TerraFlex mobile application and the Connect Map Viewer web application (where it is known as a workspace). This affects storage of data as well as coordinate display, measurement, and navigation. This includes both horizontal (projected or geographic) and vertical (geoid) components. Where possible, a Trimble geoid has been selected based on the ArcGIS vertical coordinate system (if available) or on the horizontal coordinate system (if supported).

For more information on geodetics related to high-accuracy GIS data collection workflows, consult the following site:

https://geospatialresources.trimble.com/blog/coordinate-systems-101-the-importance-of-geodetics-for-high-accuracy-gis-data-collection