Note
Go to the end to download the full example code.
Analysing a drifter dataset#
import numpy as np
import lzma
import matplotlib.pyplot as plt
import cartopy.crs as ccrs
import xarray as xr
import trajan as ta
Importing a dataset with two drifters in the Barents Sea
This follows the CF convention for trajectories https://cfconventions.org/Data/cf-conventions/cf-conventions-1.10/cf-conventions.html#_multidimensional_array_representation_of_trajectories
print(ds)
<xarray.Dataset> Size: 110kB
Dimensions: (trajectory: 2, obs: 2287)
Dimensions without coordinates: trajectory, obs
Data variables:
lon (trajectory, obs) float64 37kB 29.85 29.83 ... 21.14 21.15
lat (trajectory, obs) float64 37kB 77.3 77.31 ... 74.58 74.58
time (trajectory, obs) datetime64[ns] 37kB 2022-10-07T00:00:38 ...
drifter_names (trajectory) <U16 128B 'UIB-2022-TILL-01' 'UIB-2022-TILL-02'
Attributes: (12/13)
Conventions: CF-1.10
featureType: trajectory
geospatial_lat_min: 74.5454462
geospatial_lat_max: 77.4774768
geospatial_lon_min: 17.2058074
geospatial_lon_max: 29.8523485
... ...
time_coverage_end: 2022-11-23T13:30:28
creator_email: gauteh@met.no, knutfd@met.no
creator_name: Gaute Hope and Knut Frode Dagestad
creator_url: https://github.com/OpenDrift/opendrift
summary: Two drifters in the Barents Sea. One stranded at Ho...
title: Barents Sea drifters
A basic plot can be made very simply with Trajan

2025-06-25 09:02:08 fv-az1326-4 trajan.accessor[2399] DEBUG Detecting trajectory dimension
2025-06-25 09:02:08 fv-az1326-4 trajan.accessor[2399] DEBUG Detecting time-variable for "obs"..
2025-06-25 09:02:08 fv-az1326-4 trajan.accessor[2399] DEBUG Detected obs-dim: obs, detected time-variable: time.
2025-06-25 09:02:08 fv-az1326-4 trajan.accessor[2399] DEBUG Detected un-structured (2D) trajectory dataset
2025-06-25 09:02:08 fv-az1326-4 trajan.traj[2399] DEBUG Setting up new plot object.
2025-06-25 09:02:08 fv-az1326-4 trajan.plot[2399] DEBUG Plotting lines
2025-06-25 09:02:08 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:08 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:08 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:08 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:08 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:08 fv-az1326-4 trajan.plot[2399] DEBUG Creating new figure and axes..
2025-06-25 09:02:08 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:08 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
/home/runner/micromamba/envs/trajan/lib/python3.13/site-packages/shapely/creation.py:218: RuntimeWarning: invalid value encountered in linestrings
return lib.linestrings(coords, np.intc(handle_nan), out=out, **kwargs)
Cropping to a smaller geographical area

2025-06-25 09:02:09 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:09 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:09 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:09 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:09 fv-az1326-4 trajan.accessor[2399] DEBUG Detecting trajectory dimension
2025-06-25 09:02:09 fv-az1326-4 trajan.accessor[2399] DEBUG trajectory_id is drifter_names, but dimensions have other names: {str(list(trajectory_var.sizes))}
2025-06-25 09:02:09 fv-az1326-4 trajan.accessor[2399] DEBUG No trajectory_id attribute/variable found, trying to identify by name.
2025-06-25 09:02:09 fv-az1326-4 trajan.accessor[2399] DEBUG Detecting time-variable for "obs"..
2025-06-25 09:02:09 fv-az1326-4 trajan.accessor[2399] DEBUG Detected obs-dim: obs, detected time-variable: time.
2025-06-25 09:02:09 fv-az1326-4 trajan.accessor[2399] DEBUG Detected un-structured (2D) trajectory dataset
2025-06-25 09:02:09 fv-az1326-4 trajan.traj[2399] DEBUG Setting up new plot object.
2025-06-25 09:02:09 fv-az1326-4 trajan.plot[2399] DEBUG Plotting lines
2025-06-25 09:02:09 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:09 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:09 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:09 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:09 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:09 fv-az1326-4 trajan.plot[2399] DEBUG Creating new figure and axes..
2025-06-25 09:02:09 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:09 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
/home/runner/micromamba/envs/trajan/lib/python3.13/site-packages/shapely/creation.py:218: RuntimeWarning: invalid value encountered in linestrings
return lib.linestrings(coords, np.intc(handle_nan), out=out, **kwargs)
/home/runner/micromamba/envs/trajan/lib/python3.13/site-packages/shapely/creation.py:218: RuntimeWarning: invalid value encountered in linestrings
return lib.linestrings(coords, np.intc(handle_nan), out=out, **kwargs)
The figure can be customized, combining functionality from Trajan, Xarray and Matplotlib
ds.isel(trajectory=1).traj.plot(color='b', label=ds.trajectory[1].values,
land='mask', margin=3)
ds.isel(trajectory=0).traj.plot(color='r', label=ds.trajectory[0].values)
plt.legend()
plt.title('Two drifters in the Barents Sea')
plt.show()

2025-06-25 09:02:10 fv-az1326-4 trajan.accessor[2399] DEBUG Detecting trajectory dimension
2025-06-25 09:02:10 fv-az1326-4 trajan.accessor[2399] DEBUG Single trajectory, a trajectory dimension will be added
2025-06-25 09:02:10 fv-az1326-4 trajan.accessor[2399] DEBUG Using trajectory_id variable name (drifter_names) as trajectory dimension name
2025-06-25 09:02:10 fv-az1326-4 trajan.accessor[2399] DEBUG Detecting time-variable for "obs"..
2025-06-25 09:02:10 fv-az1326-4 trajan.accessor[2399] DEBUG Detected obs-dim: obs, detected time-variable: time.
2025-06-25 09:02:10 fv-az1326-4 trajan.accessor[2399] DEBUG Detected un-structured (2D) trajectory dataset
2025-06-25 09:02:10 fv-az1326-4 trajan.traj[2399] DEBUG Setting up new plot object.
2025-06-25 09:02:10 fv-az1326-4 trajan.plot[2399] DEBUG Plotting lines
2025-06-25 09:02:10 fv-az1326-4 trajan.accessor[2399] DEBUG Detecting trajectory dimension
2025-06-25 09:02:10 fv-az1326-4 trajan.accessor[2399] DEBUG Detecting time-variable for "obs"..
2025-06-25 09:02:10 fv-az1326-4 trajan.accessor[2399] DEBUG Detected obs-dim: obs, detected time-variable: time.
2025-06-25 09:02:10 fv-az1326-4 trajan.accessor[2399] DEBUG Detected un-structured (2D) trajectory dataset
2025-06-25 09:02:10 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:10 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:10 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:10 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:10 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:10 fv-az1326-4 trajan.plot[2399] DEBUG Creating new figure and axes..
2025-06-25 09:02:11 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:11 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:11 fv-az1326-4 trajan.accessor[2399] DEBUG Detecting trajectory dimension
2025-06-25 09:02:11 fv-az1326-4 trajan.accessor[2399] DEBUG Single trajectory, a trajectory dimension will be added
2025-06-25 09:02:11 fv-az1326-4 trajan.accessor[2399] DEBUG Using trajectory_id variable name (drifter_names) as trajectory dimension name
2025-06-25 09:02:11 fv-az1326-4 trajan.accessor[2399] DEBUG Detecting time-variable for "obs"..
2025-06-25 09:02:11 fv-az1326-4 trajan.accessor[2399] DEBUG Detected obs-dim: obs, detected time-variable: time.
2025-06-25 09:02:11 fv-az1326-4 trajan.accessor[2399] DEBUG Detected un-structured (2D) trajectory dataset
2025-06-25 09:02:11 fv-az1326-4 trajan.traj[2399] DEBUG Setting up new plot object.
2025-06-25 09:02:11 fv-az1326-4 trajan.plot[2399] DEBUG Plotting lines
2025-06-25 09:02:11 fv-az1326-4 trajan.accessor[2399] DEBUG Detecting trajectory dimension
2025-06-25 09:02:11 fv-az1326-4 trajan.accessor[2399] DEBUG Detecting time-variable for "obs"..
2025-06-25 09:02:11 fv-az1326-4 trajan.accessor[2399] DEBUG Detected obs-dim: obs, detected time-variable: time.
2025-06-25 09:02:11 fv-az1326-4 trajan.accessor[2399] DEBUG Detected un-structured (2D) trajectory dataset
2025-06-25 09:02:11 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:11 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:11 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:11 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:11 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:11 fv-az1326-4 trajan.plot[2399] DEBUG Axes already exist on existing figure.
2025-06-25 09:02:11 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:11 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
/home/runner/micromamba/envs/trajan/lib/python3.13/site-packages/shapely/creation.py:218: RuntimeWarning: invalid value encountered in linestrings
return lib.linestrings(coords, np.intc(handle_nan), out=out, **kwargs)
Trajan includes methods to e.g. calculate the speed of the drifters
Max speed 1008.360274201437 m/s
We see that the max speed > 1000 m/s, which is a numerical error due to some cases with GPS positions reported with very small time interval. By removing all positions where time interval < 5 min, we avoid this problem.
2025-06-25 09:02:11 fv-az1326-4 trajan.accessor[2399] DEBUG Detecting trajectory dimension
2025-06-25 09:02:11 fv-az1326-4 trajan.accessor[2399] DEBUG Detecting time-variable for "obs"..
2025-06-25 09:02:11 fv-az1326-4 trajan.accessor[2399] DEBUG Detected obs-dim: obs, detected time-variable: time.
2025-06-25 09:02:11 fv-az1326-4 trajan.accessor[2399] DEBUG Detected un-structured (2D) trajectory dataset
Max speed 1.2873047098224348 m/s
Likewise, one can insert breaks (NaN) in the trajectories whenever the time between points exceed a desired threshold, e.g. 3 hours
ds = ds.traj.insert_nan_where(ds.traj.time_to_next()>np.timedelta64(3, 'h'))
Plotting trajectories colored by drifter speed

2025-06-25 09:02:11 fv-az1326-4 trajan.accessor[2399] DEBUG Detecting trajectory dimension
2025-06-25 09:02:11 fv-az1326-4 trajan.accessor[2399] DEBUG Detecting time-variable for "obs"..
2025-06-25 09:02:11 fv-az1326-4 trajan.accessor[2399] DEBUG Detected obs-dim: obs, detected time-variable: time.
2025-06-25 09:02:11 fv-az1326-4 trajan.accessor[2399] DEBUG Detected un-structured (2D) trajectory dataset
2025-06-25 09:02:11 fv-az1326-4 trajan.traj[2399] DEBUG Setting up new plot object.
2025-06-25 09:02:11 fv-az1326-4 trajan.plot[2399] DEBUG Plotting lines
2025-06-25 09:02:11 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:11 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:11 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:11 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:11 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:11 fv-az1326-4 trajan.plot[2399] DEBUG Creating new figure and axes..
2025-06-25 09:02:11 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:11 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:11 fv-az1326-4 trajan.plot[2399] DEBUG Plotting trajectory 0 of 2 with color
/home/runner/micromamba/envs/trajan/lib/python3.13/site-packages/shapely/creation.py:218: RuntimeWarning: invalid value encountered in linestrings
return lib.linestrings(coords, np.intc(handle_nan), out=out, **kwargs)
2025-06-25 09:02:12 fv-az1326-4 trajan.plot[2399] DEBUG Plotting trajectory 1 of 2 with color
2025-06-25 09:02:13 fv-az1326-4 matplotlib.colorbar[2399] DEBUG locator: <matplotlib.ticker.AutoLocator object at 0x7f7494c05490>
Histogram of drifter speeds.
speed = ds.traj.speed()
plt.hist(speed.values[~np.isnan(speed.values)], 100)
plt.xlabel('Drifter speed [m/s]')
plt.ylabel('Number')
plt.show()

The peak at speed=0m/s is from the period where one of the drifters are on land (Hopen island). This can be removed simply:
speed = speed.where(speed>0.01)
plt.hist(speed.values[~np.isnan(speed.values)], 100)
plt.xlabel('Drifter speed [m/s]')
plt.ylabel('Number')
plt.show()

The positions of GPS based drifters are normally given at slightly irregular time intervals, as drifters may be without GPS coverage for periods, and may get GPX fixes irregularly. TrajAn contains the method gridtime to interpolate positions to a regular time intervel, e.g. hourly:
dh = ds.traj.gridtime('1h')
ds.traj.plot(color='r', label='raw data', land='mask')
dh.traj.plot(color='b', label='hourly')
plt.gca().set_extent([23.8, 25.0, 76.8, 77], crs=ccrs.PlateCarree()) # Zooming in to highliht differences
plt.legend()
plt.show()

2025-06-25 09:02:14 fv-az1326-4 trajan.plot[2399] DEBUG Plotting lines
2025-06-25 09:02:14 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:14 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:14 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:14 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:14 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:14 fv-az1326-4 trajan.plot[2399] DEBUG Creating new figure and axes..
2025-06-25 09:02:14 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:14 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
/home/runner/micromamba/envs/trajan/lib/python3.13/site-packages/shapely/creation.py:218: RuntimeWarning: invalid value encountered in linestrings
return lib.linestrings(coords, np.intc(handle_nan), out=out, **kwargs)
/home/runner/micromamba/envs/trajan/lib/python3.13/site-packages/shapely/creation.py:218: RuntimeWarning: invalid value encountered in linestrings
return lib.linestrings(coords, np.intc(handle_nan), out=out, **kwargs)
2025-06-25 09:02:15 fv-az1326-4 trajan.accessor[2399] DEBUG Detecting trajectory dimension
2025-06-25 09:02:15 fv-az1326-4 trajan.accessor[2399] DEBUG Detected obs-dim: time, detected time-variable: time.
2025-06-25 09:02:15 fv-az1326-4 trajan.accessor[2399] DEBUG Detected structured (1D) trajectory dataset
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG Setting up new plot object.
2025-06-25 09:02:15 fv-az1326-4 trajan.plot[2399] DEBUG Plotting lines
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:15 fv-az1326-4 trajan.plot[2399] DEBUG Axes already exist on existing figure.
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
/home/runner/micromamba/envs/trajan/lib/python3.13/site-packages/shapely/creation.py:218: RuntimeWarning: invalid value encountered in linestrings
return lib.linestrings(coords, np.intc(handle_nan), out=out, **kwargs)
/home/runner/micromamba/envs/trajan/lib/python3.13/site-packages/shapely/creation.py:218: RuntimeWarning: invalid value encountered in linestrings
return lib.linestrings(coords, np.intc(handle_nan), out=out, **kwargs)
Having the dataset on a regular time interval makes it simpler to compare with e.g. drift models, and also makes some analyses simpler
dh.isel(trajectory=0).traj.plot(color='r', label='Full trajectory')
dh.isel(trajectory=0).sel(time=slice('2022-10-10', '2022-10-12')).traj.plot(
color='k', linewidth=2, label='10-12 Oct 2022')
plt.legend()
plt.show()

2025-06-25 09:02:15 fv-az1326-4 trajan.accessor[2399] DEBUG Detecting trajectory dimension
2025-06-25 09:02:15 fv-az1326-4 trajan.accessor[2399] DEBUG Single trajectory, a trajectory dimension will be added
2025-06-25 09:02:15 fv-az1326-4 trajan.accessor[2399] DEBUG Using trajectory_id variable name (drifter_names) as trajectory dimension name
2025-06-25 09:02:15 fv-az1326-4 trajan.accessor[2399] DEBUG Detected obs-dim: time, detected time-variable: time.
2025-06-25 09:02:15 fv-az1326-4 trajan.accessor[2399] DEBUG Detected structured (1D) trajectory dataset
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG Setting up new plot object.
2025-06-25 09:02:15 fv-az1326-4 trajan.plot[2399] DEBUG Plotting lines
2025-06-25 09:02:15 fv-az1326-4 trajan.accessor[2399] DEBUG Detecting trajectory dimension
2025-06-25 09:02:15 fv-az1326-4 trajan.accessor[2399] DEBUG Detected obs-dim: time, detected time-variable: time.
2025-06-25 09:02:15 fv-az1326-4 trajan.accessor[2399] DEBUG Detected structured (1D) trajectory dataset
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:15 fv-az1326-4 trajan.plot[2399] DEBUG Creating new figure and axes..
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
/home/runner/micromamba/envs/trajan/lib/python3.13/site-packages/shapely/creation.py:218: RuntimeWarning: invalid value encountered in linestrings
return lib.linestrings(coords, np.intc(handle_nan), out=out, **kwargs)
2025-06-25 09:02:15 fv-az1326-4 trajan.accessor[2399] DEBUG Detecting trajectory dimension
2025-06-25 09:02:15 fv-az1326-4 trajan.accessor[2399] DEBUG Single trajectory, a trajectory dimension will be added
2025-06-25 09:02:15 fv-az1326-4 trajan.accessor[2399] DEBUG Using trajectory_id variable name (drifter_names) as trajectory dimension name
2025-06-25 09:02:15 fv-az1326-4 trajan.accessor[2399] DEBUG Detected obs-dim: time, detected time-variable: time.
2025-06-25 09:02:15 fv-az1326-4 trajan.accessor[2399] DEBUG Detected structured (1D) trajectory dataset
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG Setting up new plot object.
2025-06-25 09:02:15 fv-az1326-4 trajan.plot[2399] DEBUG Plotting lines
2025-06-25 09:02:15 fv-az1326-4 trajan.accessor[2399] DEBUG Detecting trajectory dimension
2025-06-25 09:02:15 fv-az1326-4 trajan.accessor[2399] DEBUG Detected obs-dim: time, detected time-variable: time.
2025-06-25 09:02:15 fv-az1326-4 trajan.accessor[2399] DEBUG Detected structured (1D) trajectory dataset
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:15 fv-az1326-4 trajan.plot[2399] DEBUG Axes already exist on existing figure.
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:15 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
The original dataset had two dimensions (trajectory, obs) (see top of page), and time is a 2D variable. For the gridded dataset (as with datasets imported from some trajectory models), dimensions are (trajectory, time) and time is a 1D Xarray dimension coordinate
print(dh)
<xarray.Dataset> Size: 46kB
Dimensions: (trajectory: 2, time: 1142)
Coordinates:
* time (time) datetime64[ns] 9kB 2022-10-07 ... 2022-11-23T13:00:00
* trajectory (trajectory) int64 16B 0 1
Data variables:
lon (trajectory, time) float64 18kB nan 29.82 29.77 ... 21.13 nan
lat (trajectory, time) float64 18kB nan 77.31 77.31 ... 74.58 nan
drifter_names (trajectory) <U16 128B 'UIB-2022-TILL-01' 'UIB-2022-TILL-02'
Attributes: (12/13)
Conventions: CF-1.10
featureType: trajectory
geospatial_lat_min: 74.5454462
geospatial_lat_max: 77.4774768
geospatial_lon_min: 17.2058074
geospatial_lon_max: 29.8523485
... ...
time_coverage_end: 2022-11-23T13:30:28
creator_email: gauteh@met.no, knutfd@met.no
creator_name: Gaute Hope and Knut Frode Dagestad
creator_url: https://github.com/OpenDrift/opendrift
summary: Two drifters in the Barents Sea. One stranded at Ho...
title: Barents Sea drifters
Plotting the velocity spectrum for one drifter

2025-06-25 09:02:16 fv-az1326-4 trajan.accessor[2399] DEBUG Detecting trajectory dimension
2025-06-25 09:02:16 fv-az1326-4 trajan.accessor[2399] DEBUG Single trajectory, a trajectory dimension will be added
2025-06-25 09:02:16 fv-az1326-4 trajan.accessor[2399] DEBUG Using trajectory_id variable name (drifter_names) as trajectory dimension name
2025-06-25 09:02:16 fv-az1326-4 trajan.accessor[2399] DEBUG Detected obs-dim: time, detected time-variable: time.
2025-06-25 09:02:16 fv-az1326-4 trajan.accessor[2399] DEBUG Detected structured (1D) trajectory dataset
/home/runner/work/trajan/trajan/trajan/traj.py:755: FutureWarning: The return type of `Dataset.dims` will be changed to return a set of dimension names in future, in order to be more consistent with `DataArray.dims`. To access a mapping from dimension names to lengths, please use `Dataset.sizes`.
lenobs = self.ds.dims[self.obs_dim]
Do a basic animation of the drift of the drifters

2025-06-25 09:02:16 fv-az1326-4 trajan.traj[2399] DEBUG Setting up new animation object.
2025-06-25 09:02:16 fv-az1326-4 trajan.animation[2399] DEBUG Animating trajectories..
2025-06-25 09:02:16 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:16 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:16 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:16 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:16 fv-az1326-4 trajan.traj[2399] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-06-25 09:02:16 fv-az1326-4 trajan.plot[2399] DEBUG Creating new figure and axes..
2025-06-25 09:02:16 fv-az1326-4 trajan.animation[2399] DEBUG Running animation.. frames: 1142
Total running time of the script: (0 minutes 8.836 seconds)