Outline Creator Tool

[enzodbspace]

Hello!

I created a tool to generate outlines of objects (such as dark nebulae or any type of contour that needs to be drawn manually). It works with Aladin Lite, points are marked directly on an image of the sky, can be moved, deleted, and then exported as CSV coordinate pairs (decimal RA hours, decimal Dec deg). This CSV file can then be used in StarPlot to plot the outline. You can also import a CSV file and edit it.

You can see the Outline Creator tool here.

Screen example:

Basic usage:

• CTRL + Click to add points.
• The three main tools: cursor only, move points, and delete points.
• Global tools: undo action and delete all.

Exported CSV file:

Coalsack-Nebula.csv

Starplot example:

Code example:

(probably not the best possible)

import csv
from pathlib import Path

import matplotlib.pyplot as plt
from shapely.geometry import LinearRing

from starplot import MapPlot, Stereographic, _
from starplot.styles import PlotStyle, PolygonStyle, extensions

SCRIPT_DIR  = Path(__file__).parent
CSV_PATH    = SCRIPT_DIR / "Coalsack-Nebula.csv"
OUTPUT_PATH = SCRIPT_DIR / "Coalsack-Nebula.png"

RA_CENTER  = 12.5 * 15.0
DEC_CENTER = -61.0
FOV        = 20.0

RESOLUTION = 1000

def load_outline(csv_path: Path) -> list[tuple[float, float]]:
    coords = []
    with open(csv_path, newline="") as f:
        reader = csv.reader(f)
        for row in reader:
            ra_deg = float(row[0]) * 15.0
            dec = float(row[1])
            coords.append((ra_deg, dec))
    return coords


def main():
    coords = load_outline(CSV_PATH)

    style = PlotStyle().extend(
        extensions.BLUE_DARK,
        extensions.MAP
    )

    half    = FOV / 2.0
    ra_min  = RA_CENTER - half
    ra_max  = RA_CENTER + half
    dec_min = DEC_CENTER - half
    dec_max = DEC_CENTER + half

    p = MapPlot(
        projection=Stereographic(center_ra=RA_CENTER, center_dec=DEC_CENTER),
        ra_min=ra_min,
        ra_max=ra_max,
        dec_min=dec_min,
        dec_max=dec_max,
        style=style,
        resolution=RESOLUTION,
        scale=0.5,
        autoscale=False,
    )

    p.constellations()
    p.constellation_borders()

    p.stars(
        where=[_.magnitude <= 7.0],
        where_labels=[False],
    )

    poly_style = PolygonStyle(
        edge_color="#618eb8",
        fill_color="#344a5e",
        edge_width=1.5,
        line_style=(0, (3, 3)),
        alpha=0.5,
        zorder=100,
    )

    # Check if the polygon is counter-clockwise, if so, reverse it to make it clockwise
    # (impact in the fill_color: inside or outside the polygon)
    if LinearRing(coords).is_ccw:
        coords = list(reversed(coords))

    # Render the outline
    p.polygon(points=coords, style=poly_style)

    p.export(str(OUTPUT_PATH), padding=0.05)
    plt.close(p.fig)
    print(f"Saved: {OUTPUT_PATH}")


if __name__ == "__main__":
    main()

I hope you find it useful for creating your own outlines 🤓

Best regards!

Enzo.

[steveberardi]

This is super awesome!! Thanks so much for building and sharing this. Looking forward to using it to create outlines for some of my favorite targets, like the Sagittarius Star Cloud 😄

I'll add a link to this on the Starplot website and include it in an upcoming newsletter.

Thanks again!

Steve