X-pos provides users who do not have the chance to do their own post-processing with a fully integrated Coordinate Computation service, which uses files contained in the X-pos repository as reference station data.
The Post-Processing > Computation page of the SBC User Portal allows users to upload RINEX rover files and automatically detects suitable reference stations among the X-pos reference sites. If these have GNSS data for the matching time interval, a coordinate computation can be performed in order to provide users with accurate rover coordinates. As rover input files, RINEX v2.x, 3.02 and 3.03 are supported.
Rover files selected by users are parsed, in order to detect their antenna and receiver type, as well as the type of data to be processed (Static, Kinematic or Stop&Go), and, above all, to read the approximate position of the rover. This is how X-pos is able to locate suitable reference sites for specific rovers, in order to execute coordinate computations. The parsed information is also displayed in a summary table located on the right side of the Computation page. Rover locations and reference stations positions are visualized on a map.
The upload of several rover files at a time is supported, no matter if referring to the same rover or to different ones, and it is possible to use different data types at a time (Static, Kinematic and/or Stop&Go): X-pos will detect, for each rover file, the most appropriate reference sites and computation methods.
The maximum size of the rover data files to be uploaded is configured in the text box "Maximum Input file size for X-pos Coordinate Computation" in the Settings->X-pos page of the Administrator portal. The limitations of this field are:
Based on the value set by the Administrator, the user is limited to that specific value when uploading rover data files in the X-pos Coordinate Computation request page.
Users have the chance to give a project name to each computation request. This is not mandatory.
Only users with a suitable subscription can benefit from the Coordinate Computation service. Please note that the Computation option is only visible on SBC User portal if the Enable Coordinate Computation Service checkbox is flagged in the Settings > X-pos > General page of the Admin portal, SBC related settings section.
Users have the possibility to enable the Virtual RINEX option when requesting a Coordinate Computation. When this option is enabled, for each of the uploaded rover files, a virtual station will be used as reference, instead of the surrounding physical ones. In this case, only single baseline results will be delivered for each rover, as only one reference file per input file will be produced. If more than one file referring to different rovers are uploaded at a time, one virtual RINEX file per rover will be created, and the same amount of baselines will be computed and contained in the computation results.
Virtual RINEX always requires a kind of GNSS network processing data: obtaining a RINEX file referring to a virtual location will be possible for those periods of time and positions for which an active cluster has provided sufficient network correction data, if successfully pushed to the X-pos data repository. Virtual reference files are created based on the real data available for the X-pos reference stations: whenever enabling the Virtual RINEX option before submitting a Coordinate Computation request on SBC User portal, the real reference stations involved in the creation of the virtual data will be displayed in the map and highlighted in blue color. The same rule for display applies to real reference stations involved in a Coordinate Computation request where the Virtual RINEX option is not in use.
When enabling the Virtual RINEX option, an extra step is required for the creation of the virtual reference file: hence, the overall Coordinate Computation process may take longer. Virtual RINEX files generated as part of the Coordinate Computation workflow will NOT be stored in the local X-pos repository.
Only users with a suitable subscription can benefit from the Virtual RINEX service. Please note that the Virtual RINEX option is only available on SBC User portal if the Enable Virtual RINEX Service checkbox is flagged in the Settings > X-pos > General page of the Admin portal, SBC related settings section.
On SBC User portal, several validations are in place every time a user uploads rover data for coordinate computations. Validity checks cover:
There may be cases when, even though enough reference stations are located for each of the selected rover files, these cannot provide any data for the required time frame. In this case, the coordinate computation is triggered but fails due to lack of reference data, and the user is notified in the Results page.
The accuracy of GNSS post processing is affected by the availability of known antenna calibration parameters for rover and reference antennas. To make sure that antennas involved in the coordinate computation are known, X-pos supports all antennas contained in the current IGS ANTEX file: a direct link (ftp://www.igs.org/pub/station/general/) to the IGS FTP source is provided on the Settings > X-pos > GNSS Antenna page of SBC Admin portal, from which administrators can download the latest IGS antenna calibration data. Once a day, X-pos automatically checks if any new IGS ANTEX files are available and, if that’s the case, it is possible to directly extend the X-pos GNSS antenna database by the latest official IGS calibrations. In addition, administrators have the option to upload their own antenna calibration file from the Custom ANTEX Import section of the GNSS Antennas page.
Every antenna contained in the uploaded ANTEX file(s) is displayed in a table on the GNSS Antennas page of the SBC Admin portal. For each entry, all relevant information is shown; fields are updated or newly added, every time a new antenna file is uploaded.
Whenever an ANTEX file is uploaded, both from local drive or FTP IGS source, this action is recorded and displayed in the Audit Log with “GNSS antenna types” as object.
To make sure that each of the X-pos reference sites has a known antenna, the antenna type is checked during the synchronization of sites between Spider and X-pos. All sites whose antenna parameters are included in the uploaded ANTEX file are marked with a green antenna indicator in the “Status” column of the Settings > X-pos > Reference Sites table. Sites whose antenna is not supported by X-pos show a red icon.
X-pos Coordinate Computation service uses a set of default parameters for its post processing. The majority of these settings cannot be customized (except for the ones in the Coordinate computation related settings section of the Settings > X-pos > General page of the SBC Admin portal: for more details please see the Coordinate computation related settings section of the X-pos Data Repository and Settings page of this help) and are summarized as follows:
The Coordinate Computation service gives users the chance to choose in which coordinate system they want results to be expressed after post-processing. Post-processing results are expressed by default in WGS84, but a coordinate transformation module is integrated in X-pos’s processing kernel, so that results can be converted to a target coordinate system selected by the user. For each Computation request, the target coordinate system can be chosen in the Computation page of SBC User portal among a group of coordinate systems made available after upload by administrators.
The only coordinate system file format supported by SBC is .csys, which is the output format for coordinate system files created with Leica Infinity. Such format is very convenient, as it supports all available components of the coordinate system in a unique file (e.g. transformations, projections, geoid and/or CSCS models, if present). Other coordinate system file formats, such as trfset.dat, are not supported by SBC.
Uploaded Coordinate System files can be visualized and handled in the Settings > X-pos > Coordinate Systems page of the Admin portal, where new files can be uploaded or removed (only if not already in use); only coordinate systems flagged as “published” will be available to users for use as target in a computation.
The actions of uploading or removing a new coordinate system file is recorded and displayed in the Audit Log with “Coordinate Systems” as object.
The selection of a particular target coordinate system before triggering a Computation request affects the way final results are provided in the Results page of SBC User portal, as well as in the final report:
The Post Processing > Results page of SBC User portal contains, in the Coordinate Computations tab, a list of all Computations triggered by the user. Each entry of the list is organized to display some basic information at a glance, while an expander on the right can be used to visualize more details about the overall computed coordinates, as well as the solution quality. When a result entry is in expanded mode, if the computation was successful, it is possible to visualize rover files details (Show File Details on the left) and to open an html report with thorough results on all the computed baselines which lead to the averaged final position.
For each selected rover file, normally multiple reference stations are found for each rover, all providing reference data for the computation. Also, it is possible to select multiple files for the same rover, each referring to different time intervals (multiple point occupation). As a consequence, multiple baselines can be formed in the computation process, all contributing to the final point solution: the post processed, accurate rover position will be a weighted average of the positions provided by all the involved baselines. This is why Coordinate Computation reports are normally organized in 3 sections:
As said, different data types can be processed by X-pos Coordinate Computation service. In case of Static rover data, the results report is organized as described above. In case Stop&Go or Kinematic data is in use, some adjustments are needed:
In the Result page of SBC User portal, when in expanded mode, a link can be clicked to display the rover trajectory (track) for kinematic computations. Also, it is possible to export the trajectory to CSV and KML format: the latter can be imported e.g. in Google Earth to visualize the track.
The Full Report available in the Results page of SBC User portal gathers all results in a unique file; when Computation results are in expanded mode, it is possible, by clicking on the “Show Results” icon, to visualize a report for each single point or track that has been processed.
Processing Static/Stop&Go and Kinematic files is allowed, in SBC, by two different products: "X-pos Coordinate Computation STATIC" and "X-pos Coordinate Computation KINEMATIC". SBC users who need to process all kinds of rover data must have both subscriptions active. The former covers computations for both Static and Stop&Go files, without distinction.