ANTEX: PCV with azimuth, full freq range, ANTEX 2, SINEX metadata #533
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Found it useful to split up the receiver antmodel into the delta+pco and the pcv, and since this is rewritten here it has been bundled in here too. An compatible antmodel() function is retained, but now using antpco() and antpcv() to avoid code duplication. Exploring using this in the pntpos and rtk paths for now, and it does make the solution much more robust to a large delta from the marker to the phase center. Separating these allows the receiver antenna delta and PCO to be applied before calculating the range and line of sight to the satellite, so that these become from the receiver phase center rather than from the marker - the calculation then seems robust to even a 1km height delta. Also the 'single' pntpos solution did not appear to even consider the delta from the marker to the ARP so was a solution for the phase center, and are people happy for the delta to be applied to the single solution so that is is also a solution for the marker position? It's a noisy solution but it is an input for the rtk solution and it appeared to be breaking the rtk solution as-is for only a few meters of height delta. There are also some other antenna delta paths that probably need fixing, that look suspect, rinex and rtcm. Does everyone expect the solution to be to the marker, so having to take into account the delta from the marker to the ARP, not the phase center solution? |
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Adding on antenna selection patches here, as there is a dependence on these changes, but kept as a separate patch, its all antenna related. This could be split out with some modification. To get it working properly still needs pntpos to be updated to account for the antenna delta, which will be in a separate PR. Tested the automated antenna selection in rtkrcv and rtknavi_qt, and it seems to be working well, and even in fixed mode it picks up the base and rover antenna type and the position from an RTCM. The windows app patches are not tested but should be close. |
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The pntpos solution has been updated to also apply the antenna delta, and also the PCO and PCV fwiw, so now calculates at the phase center and returns the position of the marker. |
This is a useful function for parsing the formatted files, so move this from rinex.c into rktcmd.c and export it.
Improve the ANTEX support. * Support PCV with azimuth. Was just NOAZI. Use linear interpolation between azimuth points, as well as the zenith. Satellite PCV still only supports NOAZI as that is most common, but all the support is there to extend this to vary with azimuth * Support ZEN1, ZEN2, DZEN, and DAZI. The PHV size is also now variable so the smallest size array is allocated. There was a fixed azimuth length of 19. It now correctly handles variations of these parameters. Require some more memory management, to free these. * Support the full range of frequencies, across systems. Was just GPS and NFREQ. The usage of the antmodel() etc functions needed to change. There were returning a NFREQ array with the offsets, but that did not work with multiple systems with different frequencies mapped to the frequency same indices - these functions are now single frequency functions. * Support PCO and PCV interpolation between frequency entries, with heuristics to avoid extrapolation of noisy data, and avoid interpolation across frequency bands (which may well be implemented with separate antenna elements e.g. stacked elements). * Add support for ANTEX 2 which avoids much redundancy. This required the PRN to SVN mapping in the SINEX satellite meta data. * Add minimal SINEX satellite meta data support, just for the PRN to SVN mappings. Adding the file-satmetafile option. * Support for the console apps. * Support for the qt apps, adding the satellite meta data file to the GUI. * Some windows app support, untested, and not yet the satellite meta data file for ANTEX 2 which needs adding to the GUI. * Adding a new function antpcv(). Implement antmodel() using the existing antpco() and the this new function to avoid code duplication, with some repetition of code execution. This is intended to allow the caller to apply the receiver PCO first and then separately the PCV, for greater accuracy, just as these are currently separated for satellites.
Implement the automated antenna type selection along with the antenna
delta from the input stream, from an RTCM or raw stream, the config
options ant{1,2}-anttype="*".
Have the config options ant{1,2}-postype RTCM and raw automatically
set the position, and independently of the antenna type, and now
including for the rover when in fixed mode.
Previously only an antenna delta would be picked up as an offset to a
base position, including a RTCM height, and only when the position was
also being automatically set and only for the base and not the rover.
Also there was no separate 'raw' antenna automated position mode, this
is included under the 'rtcm' option.
Pass in the receiver index, as a 'base' argument, which is 0 for the rover and 1 for the base, to allow the respective options to be selected rather than just using the rover options even for the base. Start making use of this: in rescode() this is now used to select the respective SNR and SNR mask. For postpos.c where a one based receiver number and zero base index were both be used, fix an instance in antpos() of indexing into option anttype[] with an one base index which would be OOB for a value of 2. Try to clean up this code in this regard.
This allows setpcv() to automatically set the antenna delta, rather than having to hack that delta into the position in antpos(), and that hack can now be removed.
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The ANTEX support was limited, perhaps good for GPS frequencies L1 and L2, but beyond that it was limited, and using more signals across multiple systems it was problematic. If the PCO is missing or wrong for some signals then that makes the solution difficult or throws it off, often showing up as an error in the height first. While addressing those issues, also added support for PCV azimuth, and for ANTEX 2 which in turn needed some limited support for satellite meta data SINEX files.
This helps if not using matched antennas, and if using a competent base for RTK.
It assumes the antennas are horizontal and pointing north. There is no support in the code yet to consider the rover heading.
Added interpolation for the receiver PCO an PCV across frequencies. If a low end antenna has at least a GPS L1 and L2 calibration then that will be used for other signals in the same band. Even supplying the L1 and L2 PCO can help and this is often printed on the label.
Some antennas with an otherwise tight PCO can vary a lot over frequency in the lower frequency band, 10mm+, so interpolation will not always be great particularly in the lower frequency band.
The ANTEX 2 files are at https://files.igs.org/pub/station/general/atx_alternative/atx2/ and the meta data at https://files.igs.org/pub/station/general/ ANTEX 2 adds nothing over ANTEX 1 for the solution and should give the same solution, it was just a small thing to add support while look over this code. ANTEX 2 has less redundant information, almost half the file size. Some example options for ANTEX 2:
file-satmetafile =igs_satellite_metadata.snx
file-satantfile =igs20_sat.atx2
file-rcvantfile =igs20_rcv.atx2
The windows app GUI support is not done, that just means there is no file selection for the ANTEX 2 meta data file, it should otherwise work, and ANTEX 2 adds nothing to the solution.