As part of the support for local coordinate system workflows in TerraFlex v5, the functionality and user experience for managing base station reference positions has been improved in Trimble Positions Desktop add-in v10.8.1.1. Instead of splitting up the information between two tabs in Base Station Properties, we have consolidated the reference position information into one tab, and provided explicit control over reference position handling in post-processing workflows: use the reference position from the database (list), use the reference position from the base station RINEX files, or let Trimble Positions decide based on project geodetic settings (currently applies only to TerraFlex workflows; see this article for more information).
The text below describes the options available on this form, with the same content being available from within the app by clicking on the More info link on the form itself.
Base Station Properties: Reference Position
Base station reference position information is displayed here. Base stations in the Trimble database (CBS list) will have at least one reference position, typically for a global datum or frame (e.g., WGS 1984) but can also have additional reference positions in other datums or even epochs. Base station data files will also typically have a reference position, the datum and epoch of which varies by provider. In general, this information cannot be changed by the user except for custom or user base station entries. All coordinate system information in this area uses a Trimble definition.
Reference position(s) from database
The reference position(s) contained in the Trimble database for this base station, expressed in latitude, longitude, and altitude, along with the datum or frame.
In the classic CBS list distributed by Trimble, there is a single reference position per base station - this is indicated here as ‘(classic / legacy)’. Future distribution of CBS data will include multiple reference positions (one per datum + epoch) per base station but they can be added manually now. Base station providers typically provide authoritative reference positions in datums other than the global WGS/ITRF. Use the ‘Edit…’, ‘Add…’, and ‘Delete’ buttons to manage the reference positions for user base stations.
Reference position from base data files (in ECEF coordinates)
The datum or frame of the reference position seeded in the base station data files (e.g., the RINEX file header). This is generally expressed as an Earth-centered, Earth-fixed coordinate.
This critical piece of information is typically included for each base station in the CBS list and is obtained from the base station provider. Use the ‘Change…’ button to manage the datum of the base data file reference position for user base stations.
Handling for differential correction
The setting for how base station reference positions should be used in post-processing. There are 3 choices:
- Use best match for current project geodetic settings (default)
The reference position will be selected from EITHER the database OR the base data files depending on what is a better match based on the geodetics of the project. For the ‘Minimize Transformations’ project geodetic workflow, it will use the reference position in the same datum from either source (base files first). For the ‘Classic’ project geodetic workflow, it will use the reference position in the WGS 1984 global datum from either source (base files first) and if one does not exist, the first one from the database will be used and transformed from the specified datum to WGS 1984 at the start of post-processing. In the database, the ‘(classic / legacy)’ position is assumed to be WGS 1984.
- Use only reference position from base station data files
Only select the reference position from the base station data files. For the ‘Minimize Transformations’ project geodetic workflow, the reference position datum must match the project GNSS storage datum for this base station to be available for use in post-processing. For the ‘Classic’ project geodetic workflow, the reference position will be transformed from the specified datum to WGS 1984 at the start of post-processing.
- Use only reference positions from database
Only select a reference position from the database. For the ‘Minimize Transformations’ project geodetic workflow, a reference position using the datum of the project GNSS storage must be available in the database in order for the base station to be available for use in post-processing. For the ‘Classic’ project geodetic workflow, a global WGS 1984 reference position from the database will be used and if one does not exist, the first one from the database will be used and transformed from the specified datum to WGS 1984 at the start of post-processing. In the database, the ‘(classic / legacy)’ position is assumed to be WGS 1984.
For More Information
For more information on geodetics related to high-accuracy GIS data collection workflows, consult this site.