SNR, Pstd, Lstd: float rather than compressed encoding #506
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ourairquality
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Store the SNR as a float, rather than a uint16_t, avoiding the scaling and rounding at each access. The comnav and tersus decoders were not even using the SNR_UNIT for scaling, perhaps another encoding, but assume scaling is not need when stored as a float. Store the P and L std in the float format. Makes better use of the input format, without lossly compression. Avoids having to do the encoding and decoding to the compressed format at each use. Implement the compressed encoding in RINEX input and output. Easier to make changes in one location here, and avoids this lossy compression on other paths. This uses a little extra storage, but if this is an issue then it might be better to abstract a compressed encoding into accessor functions than to have this distributed to each use. The P and L std might be made a compilation option. ublox: decode_trkmeas is estimating Lstd so have it respect the -RCVSTDS option. unicore: was not initialising P and L std.
For now only enabled when extended observations are enabled.
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This data, the observation SNR, Pstd and Lstd, used a compressed encoding were a float is the natural representation. These were being encoded and decoder when used, making a lot of redundant code and a burden to get right. This proposal just uses a float for these, simplifying code.
If the extra storage space is shown to be an issue then this path would still be proposed, but also adding common access functions for compressed encoding and decoding. If the L and P std are not generally useful data then this code could also become a compilation conditional to save using any storage for these if not needed. Having the code readable and maintainable seems more important to me than saving a bit of storage for these.
The Pstd and Lstd encodings were aligned with the ublox output, with a further compression to digits 1 to 9 for RINEX. This proposal moves this encoding into rinex.c, specific to the RINEX format. Raw formats decoded to RINEX should give the same output, and should read back the same float values. Changes to this encoding can now be local to rinex.c, and all uses need not be updated. The raw formats can be decoded to floats without compression to the limited RINEX encoding, and this even helps a little for the ublox format, and gives much better data for sbf and unicore formats.
Added support to the rtknavi-qt monitor observation page to output the P and L Std which was now simpler to do.