Sites and detector layouts

Every GRAND file places its detection units relative to an origin on the Earth. This page shows where that origin and the positions are stored, which sites and layouts the repository knows and how to bring a layout file into the array frame. Coordinates and conventions explains the frames themselves.

Where a file keeps its positions

TRun field

Holds

site

The site’s name, as Dunhuang or Xiaodushan

site_layout

The layout’s name, as GP13, GP80 or GP300

origin_geoid

The origin of the array frame: latitude and longitude in degrees, height in meters above the geoid

du_xyz

Each unit’s position in the array frame, in meters: x north, y west, z up

du_geoid

Each unit’s latitude, longitude and height

Simulations get these from sim2root.py: the site and layout from -s and -sl, the origin from -la, -lo and -al or, without them, from the shower simulation. Measured files also carry each unit’s GPS position with every event (Working with measured data).

Sites in the repository

Where

Latitude, longitude, height

Used by

GP13 and GP80, Dunhuang

40.98°, 93.95°, about 1200 m

Docstring examples; the GPS positions of GP80 (grand.aoi)

Xiaodushan

40.99°, 93.94°, 1264 m

The committed ZHAireS samples

Dunhuang, CoREAS table

40.142°, 94.662°, 1142 m

CoreasToRawROOT.py

Lenghu, CoREAS table

38.735°, 93.331°, 2800 m

CoreasToRawROOT.py

Default array origin

38.888°, 92.286°, 2921 m

GRANDCS without a location

The default array origin is the center of an early GP300 layout and a placeholder: GRANDCS warns when it is used. Always give the origin of your own data.

The committed CoREAS sample (sim_Dunhuang_20170401_...) stores its origin height in centimeters, 114200; files converted since use meters.

Layout files

File

Format

examples/geo/trial_GP300_layout_2021.txt

234 positions of a 2021 GP300 design: longitude, latitude (deg), height (m)

examples/eventviewer/GP300propsedLayout.dat

288 positions of the GP300 layout proposed in 2021: index, name, x, y, z (m, array frame)

sim2root/ZHAireSRawRoot/*/antpos.dat

The antennas of a ZHAireS simulation: index, name, x, y, z (m)

sim2root/CoREASRawRoot/GP300.list

The antennas of a CoREAS simulation, in CORSIKA’s format: x, y, z in cm

Whether either GP300 file matches the units deployed today is not recorded in the repository; take the positions of deployed units from the data.

From latitude and longitude to the array frame

GRANDCS puts geodetic positions in the frame of an origin you choose. Here the 2021 GP300 design, with its center as the origin:

from pathlib import Path

import numpy as np
import matplotlib.pyplot as plt
import grand
from grand import Geodetic, GRANDCS

LAYOUT = Path(grand.__file__).parents[1] / "examples/geo/trial_GP300_layout_2021.txt"
lon, lat, height = np.loadtxt(LAYOUT, unpack=True)

origin = Geodetic(latitude=lat.mean(), longitude=lon.mean(), height=height.mean())
xyz = np.asarray(GRANDCS(Geodetic(latitude=lat, longitude=lon, height=height),
                         location=origin))       # (3, units), m: x north, y west, z up

fig, ax = plt.subplots(figsize=(6, 4))
ax.scatter(-xyz[1] / 1e3, xyz[0] / 1e3, c=xyz[2], s=12, cmap="terrain")
ax.set_xlabel("east [km]")
ax.set_ylabel("north [km]")
ax.set_aspect("equal")
plt.show()
print("%d units over %.0f km north-south and %.0f km east-west"
      % (xyz.shape[1], np.ptp(xyz[0]) / 1e3, np.ptp(xyz[1]) / 1e3))
_images/sites_0_0.png 
234 units over 12 km north-south and 32 km east-west

The z coordinate falls away from the origin because the frame is tangent to the Earth at the origin: a unit at the same height 15 km away is about 18 m below the tangent plane. The colors show z, which adds that curvature to the terrain.

To write these positions into a run of your own, see Writing your own files.

Generating a layout

create_grid_univ in examples/geo/grids.py generates regular layouts from the size of one hexagonal cell, in meters: rectangular (rect), hexagonal (hexhex), hexagonal with randomly displaced units (hexrand) and hexagons with their centers (trihex). It writes new_antpos.dat and returns the positions. For simulation input, write the result as name x y z in meters (Producing simulations).

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