fchart3 0.12.2
Collection of Python scripts to make beautiful deepsky charts in various formats
Requires Python: >=3.0
Keywords: fchart3 starchart star charts finder chart astronomy map

# Fchart3

**Fchart3** is a Python project for creating high-quality astronomical finder charts and maps.
It uses data and catalogues based on Stellarium, KStars, HNSky and Gaia-derived deep star catalogues (hundreds of millions of stars, typically up to ~16–17 mag depending on the used catalog set).

In addition to single-object charts, the package also includes **fchart3-atlas** – a generator for **multi-page sky atlases** built on top of the same rendering engine.

It can generate:

- **Offline charts** with output to **PDF**, **PNG**, **SVG** or **TikZ**.
- **Online interactive charts** – the same rendering engine is used in the [**CzSkY**](https://www.czsky.eu) project.

![fchart3](https://github.com/skybber/fchart3/assets/2523097/7748f1fd-4751-4586-ac4c-7c2900d66568)

---

## Online interactive version (CzSkY)

Interactive web charts using the fchart3 engine are available in the [**CzSkY**](https://www.czsky.eu) project:

- [CzSkY Chart](https://www.czsky.eu/chart?ra=1.532197702857378&dec=0.06961660554646551&fsz=100&splitview=true)

---

## Features

- Deep-sky finder charts based on Gaia-derived star catalogues (hundreds of millions of stars).
- Deep-sky catalogue with hundreds of thousands of objects (from HNSky).
- Output formats: **PDF**, **PNG**, **SVG**, **TikZ** (format is determined by `--output-file` extension).
- Multiple projections:
  - **stereographic** (default)
  - **orthographic**
  - **equidistant** (fisheye-like)
- Equatorial **and** horizontal coordinate workflows:
  - Equatorial maps (RA/Dec).
  - Horizontal (Alt/Az) maps with observer location and time.
  - CLI supports parsing both RA/Dec and Alt/Az positions.
- Solar system rendering (Sun, Moon, planets; and planetary moons):
  - realistic radii and phases
  - Saturn ring orientation
  - optional moon magnitudes / label placement (as supported by the engine)
- Optional comet / minor planet resolving with trajectory plotting (requires time window).
- Optional polygon horizon from **Stellarium landscape** (`landscape.ini`) for Alt/Az charts.
- Flexible configuration: magnitude limits, labels, fonts, legends, colors, line widths, etc.
- Used as the map engine of the CzSkY online star atlas.

---

## Install

Recommended: install from Git into a virtual environment:

```bash
git clone https://github.com/skybber/fchart3.git
cd fchart3

python3 -m venv venv
source venv/bin/activate

pip install -r requirements.txt
pip install ./
````

### Linux build dependencies (common)

On some systems you may need development packages for Cairo and build tools before installing (example for Ubuntu):

```bash
sudo apt update
sudo apt install -y python3-dev pkg-config libcairo2-dev build-essential
```

Then:

```bash
pip install -U pip setuptools wheel
pip install pycairo
pip install .
```

### Windows

```bat
git clone https://github.com/skybber/fchart3.git
cd fchart3

python -m venv venv
venv\Scripts\activate

pip install -U pip setuptools wheel
pip install .
```

---

## Run

Show all CLI options:

```bash
fchart3 --help
```

Basic chart (default PDF) for Crab Nebula:

```bash
fchart3 M1
```

### Output file / format

The output format is defined by `--output-file` extension:

* `something.pdf`
* `something.png`
* `something.svg`
* `something.tikz`

Example (PNG):

```bash
fchart3 --output-dir out --output-file m31.png M31
```

Example (TikZ):

```bash
fchart3 --output-dir out --output-file m39.tikz M39
```

### Example: “complex” chart (PDF)

```bash
fchart3 -W 190 -H 270 -fov 40 -ls 9 -ld 9 \
  --show-nebula-outlines --show-enhanced-milky-way \
  --font-style-bayer bold --font-style-dso italic \
  --flamsteed-numbers-only --show-equatorial-grid \
  --hide-map-orientation-legend --hide-map-scale-legend \
  m39
```

> Notes:
>
> * `-ls/--limit-star` controls star limiting magnitude.
> * `-ld/--limit-dso` controls DSO limiting magnitude.
> * `-fov/--fieldsize` is the **diameter** of the field of view (degrees).

---

## Sources (what you can pass on CLI)

A “source” can be:

* DSO names: `NGC891`, `IC1396`, `M31`, …
* Special: `ALLMESSIER` (renders maps for all Messier objects)
* Explicit coordinates:

### Explicit equatorial position (RA,Dec)

```bash
fchart3 "9:35:00.8,-34:15:33,SomeCaption"
```

* RA is interpreted as **hours** (sexagesimal or decimal).
* Dec is interpreted as **degrees** (sexagesimal or decimal).

### Explicit horizontal position (Az,Alt)

Prefix the first component with `h:` (or `hor:` / `altaz:`) and use degrees:

```bash
fchart3 --coord-system horizontal -L 14.42 -A 50.08 -t now \
  "h:180:00:00,45:00:00,AzAltCaption"
```

Decimal degrees are also accepted:

```bash
fchart3 --coord-system horizontal -L 14.42 -A 50.08 -t now \
  "h:180.5,45.25,AzAltCaption"
```

> Horizontal coordinates (`h:`) are allowed **only** when `--coord-system horizontal` is selected.

---

## Observer location, time and coordinate systems

### Coordinate system

* Default: `--coord-system equatorial`
* Horizontal: `--coord-system horizontal` (Alt/Az)

### Observer longitude/latitude

Required for horizontal charts and for time-dependent objects:

```bash
-L, --obs-longitude   Observer longitude in degrees (east positive)
-A, --obs-latitude    Observer latitude in degrees
```

### Observation time

Use ISO-8601 UTC time or `now`:

```bash
-t now
-t 2026-01-02T21:15:00Z
-t 2026-01-02T21:15:00+01:00
```

---

## All-sky (fisheye) mode

Fchart3 CLI supports a convenience **all-sky** mode for rendering a **visible hemisphere** (zenith-centered) fisheye chart.

It is designed for quick “what’s up now” sky maps and works best with the **equidistant** (azimuthal equidistant / fisheye-like) projection.

### `--all-sky`

`--all-sky` is a shortcut that forces a suitable configuration:

* `--coord-system horizontal`
* `--projection equidistant`
* if `-fov/--fieldsize` is not set: `-fov 180` (full visible hemisphere)
* if `-t` is not set: uses `now` (UTC)

It **requires observer location** (`-L/-A`).

Example:

```bash
fchart3 --all-sky --font-size 2 -ls 6 -ld 6 -L 14.42 -A 50.08
```

With explicit time:

```bash
fchart3 --all-sky --font-size 2 -ls 6 -ld 6 -L 14.42 -A 50.08 -t 2026-01-02T21:15:00Z
```

### Notes

* All-sky charts are typically used with:

  * `--show-horizon` (draw the horizon circle)
  * optional `--clip-to-horizon` (hide objects below the horizon, if enabled in the engine)
* For best results on portrait paper, consider using a square-ish page size or landscape orientation,
  because an all-sky chart is circular.

---

## Stellarium landscape horizon (optional)

You can load a Stellarium landscape directory (must contain `landscape.ini`) and use its polygon horizon.
It can also provide location metadata (lon/lat) if present:

```bash
fchart3 --coord-system horizontal -t now \
  --stellarium-landscape "/path/to/stellarium/landscapes/MyLandscape" \
  "h:220,12,LookHere"
```

---

## Extra marks (crosses)

Add a cross mark with `-x`:

Format:

* `"c1,c2[,label[,pos]]"`
* `pos` = `t|b|l|r` (top/bottom/left/right)

Equatorial cross (RA/Dec):

```bash
fchart3 -x "20:35:25.4,+60:07:17.7,SN,t" NGC6946
```

Horizontal cross (Az/Alt; requires horizontal mode):

```bash
fchart3 --coord-system horizontal -L 14.42 -A 50.08 -t now \
  -x "h:180,45,Mark,r" "h:180,45,Center"
```

---

## Solar system objects

Enable solar system rendering:

```bash
fchart3 --show-solar-system -t now -L 14.42 -A 50.08 Jupiter
```

> For meaningful results, solar system objects require:
>
> * `-t` time
> * observer lon/lat (or a Stellarium landscape that provides them)

---

## Comets and minor planets (MPC) + trajectories

Fchart3 can resolve comets and minor planets using MPC files and plot their trajectories,
when you provide a time window:

Required:

* `-t` observation time
* `--trajectory-from` and `--trajectory-to` (UTC; date or datetime)

Example:

```bash
fchart3 -t 2026-01-02T21:00:00Z \
  --trajectory-from 2026-01-02 \
  --trajectory-to   2026-01-09 \
  "C/2023 A3"
```

MPC files are downloaded automatically if missing:

* `CometEls.txt` (comets)
* `MPCORB.9999.DAT` (subset of numbered minor planets)

You can override paths and force refresh:

```bash
fchart3 --mpc-comets-file ./CometEls.txt --update-comets ...
fchart3 --mpc-minor-planets-file ./MPCORB.9999.DAT --update-minor-planets ...
```

---

## Data files

This repository contains catalogues in `data/catalogs` (selection):

* `bsc5.dat` – bright stars catalogue
* `constbnd.dat` – constellation boundaries
* `constellationship_western.fab` – constellation lines (Stellarium)
* `milkyway.dat`, `milkyway_enhanced.dat` – Milky Way outlines/shading
* `deep_sky.hnd` – deep-sky objects from HNSky (Han Kleijn)
* `outlines_catgen.dat` – nebula outlines (OpenNGC-based)
* `PGC.dat`, `PGC_updates.dat` – PGC galaxy catalogue (+ updates)
* `namedstars.dat`, `starnames.dat`, `unamedstars.dat` – star name catalogues (KStars)
* `stars_0_0v*.cat` – Gaia-based deep star catalogues (Stellarium)

Runtime-downloaded (not stored in repo by default):

* `CometEls.txt` (MPC comet elements)
* `MPCORB.9999.DAT` (MPCORB subset)

---


## fchart3-atlas (multi-page sky atlas generator)

`fchart3-atlas` is included in the **fchart3** package and builds on top of the `fchart3` CLI.  
It generates a **multi-page sky atlas** by repeatedly rendering many overlapping chart tiles – similar in spirit to classic printed atlases

### What it does

- Splits the sky into a grid of **tiles** (pages) based on:
  - `--field-deg` (tile field-of-view diameter in degrees)
  - `--overlap` (tile overlap fraction to avoid gaps)
- For each tile, calls `fchart3` with an explicit RA/Dec position source:
  - `"RA,Dec,Caption"`
- Writes one output file per tile (PDF by default).
- Optionally merges all PDFs into a single `atlas.pdf` (if a PDF merge tool is available).

### Usage

Basic example (produce many pages into `./atlas_out`):

```bash
fchart3-atlas \
  --out ./atlas_out \
  --config default \
  --field-deg 60 \
  --overlap 0.20 \
  --limit-star 8.0 \
  --limit-dso 9.0 \
  --projection stereographic \
  --show-enhanced-milky-way  
```

---

## Authors

* **Vladimir Dvorak** – fchart3
* **Georg Zotti** – fchart3
* **Michiel Brentjens** – original author of fchart
* **Austin Riba** – modern fchart for Python 2.7 + NumPy: [https://github.com/Fingel/fchart](https://github.com/Fingel/fchart)

---

## License

GNU GPL v2 (or later). See `LICENSE`.