2.3.6. The Quality Page

The other five pages work on the campaign. This one works on one observation file, in detail, and answers the question you ask whenever a baseline will not fix: what is actually in this file?

It needs no RTKLIB engine — the Quality page works even on a machine where processing is unavailable.

2.3.6.1. Running a Report

The list on the left holds every observation file the project has scanned, labelled by point name. Select one and press Analyse file.

Reading is done on a background thread with a percentage readout, so a large file does not freeze the application. Every navigation file the project has scanned is offered to the analysis, so you do not have to work out which ephemeris file matches which observation file.

Note

A file whose header has no APPROX POSITION XYZ cannot be analysed: without a receiver position there is no way to compute an azimuth and elevation for any satellite. The module says so rather than drawing an empty sky plot.

2.3.6.2. The Headline

The single most useful line the page produces sits at the top:

Epochs 3610 / 3610 (100.0 % complete) at 1.0 s -- total gap 0 s (0 epoch(s))

It compares the epochs actually present against the epochs the header’s interval and time span say there should be. A file with a gap reads, for example, Epochs 3450 / 3610 (95.6 % complete) at 1.0 s -- total gap 160 s (160 epoch(s)).

Warning

INTERVAL is optional in RINEX 3. When it is absent there is nothing to compare against, and the headline says exactly that:

3610 epochs present. Completeness unknown: this file's header
carries no INTERVAL, so there is nothing to compare against.

It deliberately does not print a comforting “100 % complete” computed from an assumption.

Below it, the receiver position used for the sky geometry, together with where it came from:

Receiver position (4595220.123, 2039445.678, 3912675.901) m ECEF --
source: RINEX header (APPROX POSITION XYZ)

Naming the source matters: an APPROX POSITION several kilometres out is a real and common header error, and it will visibly distort the sky plot.

2.3.6.3. The Satellite Table

One row per satellite, sorted worst first — fewest epochs, then lowest SNR, then most cycle slips — so the satellite that is hurting you is at the top of the list rather than somewhere down a scroll.

Column

Meaning

SVID

Satellite identifier, including its constellation letter.

Epochs

Epochs in which this satellite was tracked.

%

Those epochs as a percentage of the epochs expected for the file.

Mean SNR / Min SNR

Signal-to-noise ratio over the occupation.

Slips

Cycle slips detected. This is the column the table exists for.

Row colours flag the slip count: orange for any slips at all, red for 100 or more. A four-figure slip count on one satellite over a two-hour occupation is the kind of thing that must jump out rather than read as one more number in a column.

Note

A satellite whose constellation declares no SNR observable shows -- in the two SNR columns, not 0.0. A fabricated zero would be both wrong and — because the sort is worst-first — would drag a perfectly healthy satellite to the top of the table.

2.3.6.4. Satellites That Could Not Be Plotted

Under the plots, a note names any satellite whose sky track is missing, partial, or drawn without SNR, and says why — distinguishing, for example, “no ephemeris record anywhere” from “the nearest ephemeris record is 24 hours away”.

This exists because the alternative is worse: a satellite that is simply absent from the sky plot, with nothing said about it, invites you to conclude the receiver never tracked it. The commonest cause is mundane — the rover tracked GLONASS and the campaign only downloaded a GPS navigation file.

At most three notes are shown, with a count of how many more share the same kind of problem.

2.3.6.5. The Plots

2.3.6.5.1. Sky plot

A polar view from the receiver: north at the top, east to the right, the horizon at the outer edge and the zenith at the centre. Each satellite’s track through the occupation is drawn as a line, labelled with its SVID and coloured by SNR.

This is where obstructions become obvious — a wedge of sky with no tracks in it is a building, a tree line or a cut face, and it will explain both the slips and the geometry.

2.3.6.5.2. SNR over time

Signal-to-noise ratio against time, per satellite. Multipath shows here as a regular oscillation; an obstruction shows as a sudden drop that recovers.

2.3.6.5.3. Satellites tracked

A bar chart of how many satellites were tracked in each time bin.

  • Blue bars are bins with the epochs they should have.

  • Red bars are bins short of their expected epochs — a data gap.

  • Hatched bars are bins the file only partly covers, because the occupation started or ended part-way through the bin. A hatched bar is normal at the two ends of the chart; hatched and red means it is also short.

If the header carries no INTERVAL, the chart says so in words and leaves every bar plain, rather than shading bars on the strength of an assumption.

2.3.6.6. Using the Quality Page

The practical workflow when a baseline will not fix:

  1. Analyse both ends of the baseline.

  2. Check the headline. A file that is 60 % complete has a problem no solver setting will fix.

  3. Look at the top of the satellite table. Heavy slips concentrated in one constellation are an argument for unticking that constellation on the Processing page.

  4. Look at the sky plot for obstructions. A blocked horizon is an argument for raising the elevation mask.

  5. Look at the satellite-count chart. A red band in the middle of the occupation is a gap you can cut out with the Start and End fields on the Processing page.