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gnss-sdr/utils/skyplot/README.md

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# GNSS Skyplot utility
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[comment]: # (
SPDX-License-Identifier: GPL-3.0-or-later
)
[comment]: # (
SPDX-FileCopyrightText: 2025 Carles Fernandez-Prades <carles.fernandez@cttc.es>
)
<!-- prettier-ignore-end -->
A Python script that generates polar skyplots from RINEX navigation files,
showing satellite visibility over time.
## Features
- Processes RINEX navigation files.
- Calculates satellite positions using broadcast ephemeris.
- Plots satellite tracks in azimuth-elevation coordinates.
- Color-codes satellites by constellation (GPS, Galileo, GLONASS, BeiDou).
- Customizable observer location.
- Outputs high-quality image in PDF format.
- Non-interative mode for CI jobs (with `--no-show` flag).
## Requirements
- Python 3.6+
- Required packages:
- `numpy`
- `matplotlib`
## Usage
### Basic Command
```
./skyplot.py <RINEX_FILE> [LATITUDE] [LONGITUDE] [ALTITUDE] [--no-show]
```
### Arguments
| Argument | Type | Units | Description | Default |
| ------------ | -------- | ----------- | ---------------------- | -------- |
| `RINEX_FILE` | Required | - | RINEX nav file path | - |
| `LATITUDE` | Optional | degrees (°) | North/South position | 41.275°N |
| `LONGITUDE` | Optional | degrees (°) | East/West position | 1.9876°E |
| `ALTITUDE` | Optional | meters (m) | Height above sea level | 80.0 m |
| `--no-show` | Optional | - | Do not show plot | - |
### Examples
- Skyplot from default location (Castelldefels, Spain):
```
./skyplot.py brdc0010.22n
```
- Skyplot from custom location (New York City, USA):
```
./skyplot.py brdc0010.22n 40.7128 -74.0060 10.0
```
- Skyplot from custom location (Santiago, Chile):
```
./skyplot.py brdc0010.22n -33.4592 -70.6453 520.0
```
- Non-interactive mode (for CI jobs):
```
./skyplot.py brdc0010.22n -33.4592 -70.6453 520.0 --no-show
```
## Output
The script generates a PDF file named `skyplot_<RINEX_FILE>.pdf` (with dots in
`<RINEX_FILE>` replaced by `_`) with:
- Satellite trajectories over all epochs in the file.
- Color-coded by constellation.
- Observer location in title.
- Time range in footer.