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

2025-09-09 15:16:48 runnervmf4ws1 trajan.accessor[2509] DEBUG Detecting trajectory dimension
2025-09-09 15:16:48 runnervmf4ws1 trajan.accessor[2509] DEBUG Detecting time-variable for "obs"..
2025-09-09 15:16:48 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected obs-dim: obs, detected time-variable: time.
2025-09-09 15:16:48 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected un-structured (2D) trajectory dataset
2025-09-09 15:16:48 runnervmf4ws1 trajan.traj[2509] DEBUG Setting up new plot object.
2025-09-09 15:16:48 runnervmf4ws1 trajan.plot[2509] DEBUG Plotting lines
2025-09-09 15:16:48 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:48 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:48 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:48 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:48 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:48 runnervmf4ws1 trajan.plot[2509] DEBUG Creating new figure and axes..
2025-09-09 15:16:48 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:48 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
Cropping to a smaller geographical area

2025-09-09 15:16:49 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:49 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:49 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:49 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:49 runnervmf4ws1 trajan.accessor[2509] DEBUG Detecting trajectory dimension
2025-09-09 15:16:49 runnervmf4ws1 trajan.accessor[2509] DEBUG trajectory_id is drifter_names, but dimensions have other names: {str(list(trajectory_var.sizes))}
2025-09-09 15:16:49 runnervmf4ws1 trajan.accessor[2509] DEBUG No trajectory_id attribute/variable found, trying to identify by name.
2025-09-09 15:16:49 runnervmf4ws1 trajan.accessor[2509] DEBUG Detecting time-variable for "obs"..
2025-09-09 15:16:49 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected obs-dim: obs, detected time-variable: time.
2025-09-09 15:16:49 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected un-structured (2D) trajectory dataset
2025-09-09 15:16:49 runnervmf4ws1 trajan.traj[2509] DEBUG Setting up new plot object.
2025-09-09 15:16:49 runnervmf4ws1 trajan.plot[2509] DEBUG Plotting lines
2025-09-09 15:16:49 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:49 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:49 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:49 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:49 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:49 runnervmf4ws1 trajan.plot[2509] DEBUG Creating new figure and axes..
2025-09-09 15:16:49 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:49 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
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()

2025-09-09 15:16:50 runnervmf4ws1 trajan.accessor[2509] DEBUG Detecting trajectory dimension
2025-09-09 15:16:50 runnervmf4ws1 trajan.accessor[2509] DEBUG Single trajectory, a trajectory dimension will be added
2025-09-09 15:16:50 runnervmf4ws1 trajan.accessor[2509] DEBUG Using trajectory_id variable name (drifter_names) as trajectory dimension name
2025-09-09 15:16:50 runnervmf4ws1 trajan.accessor[2509] DEBUG Detecting time-variable for "obs"..
2025-09-09 15:16:50 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected obs-dim: obs, detected time-variable: time.
2025-09-09 15:16:50 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected un-structured (2D) trajectory dataset
2025-09-09 15:16:50 runnervmf4ws1 trajan.traj[2509] DEBUG Setting up new plot object.
2025-09-09 15:16:50 runnervmf4ws1 trajan.plot[2509] DEBUG Plotting lines
2025-09-09 15:16:50 runnervmf4ws1 trajan.accessor[2509] DEBUG Detecting trajectory dimension
2025-09-09 15:16:50 runnervmf4ws1 trajan.accessor[2509] DEBUG Detecting time-variable for "obs"..
2025-09-09 15:16:50 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected obs-dim: obs, detected time-variable: time.
2025-09-09 15:16:50 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected un-structured (2D) trajectory dataset
2025-09-09 15:16:50 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:50 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:50 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:50 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:50 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:50 runnervmf4ws1 trajan.plot[2509] DEBUG Creating new figure and axes..
2025-09-09 15:16:51 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:51 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:51 runnervmf4ws1 trajan.accessor[2509] DEBUG Detecting trajectory dimension
2025-09-09 15:16:51 runnervmf4ws1 trajan.accessor[2509] DEBUG Single trajectory, a trajectory dimension will be added
2025-09-09 15:16:51 runnervmf4ws1 trajan.accessor[2509] DEBUG Using trajectory_id variable name (drifter_names) as trajectory dimension name
2025-09-09 15:16:51 runnervmf4ws1 trajan.accessor[2509] DEBUG Detecting time-variable for "obs"..
2025-09-09 15:16:51 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected obs-dim: obs, detected time-variable: time.
2025-09-09 15:16:51 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected un-structured (2D) trajectory dataset
2025-09-09 15:16:51 runnervmf4ws1 trajan.traj[2509] DEBUG Setting up new plot object.
2025-09-09 15:16:51 runnervmf4ws1 trajan.plot[2509] DEBUG Plotting lines
2025-09-09 15:16:51 runnervmf4ws1 trajan.accessor[2509] DEBUG Detecting trajectory dimension
2025-09-09 15:16:51 runnervmf4ws1 trajan.accessor[2509] DEBUG Detecting time-variable for "obs"..
2025-09-09 15:16:51 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected obs-dim: obs, detected time-variable: time.
2025-09-09 15:16:51 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected un-structured (2D) trajectory dataset
2025-09-09 15:16:51 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:51 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:51 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:51 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:51 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:51 runnervmf4ws1 trajan.plot[2509] DEBUG Axes already exist on existing figure.
2025-09-09 15:16:51 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:51 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
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.
2025-09-09 15:16:51 runnervmf4ws1 trajan.accessor[2509] DEBUG Detecting trajectory dimension
2025-09-09 15:16:51 runnervmf4ws1 trajan.accessor[2509] DEBUG Detecting time-variable for "obs"..
2025-09-09 15:16:51 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected obs-dim: obs, detected time-variable: time.
2025-09-09 15:16:51 runnervmf4ws1 trajan.accessor[2509] 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

2025-09-09 15:16:51 runnervmf4ws1 trajan.accessor[2509] DEBUG Detecting trajectory dimension
2025-09-09 15:16:51 runnervmf4ws1 trajan.accessor[2509] DEBUG Detecting time-variable for "obs"..
2025-09-09 15:16:51 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected obs-dim: obs, detected time-variable: time.
2025-09-09 15:16:51 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected un-structured (2D) trajectory dataset
2025-09-09 15:16:51 runnervmf4ws1 trajan.traj[2509] DEBUG Setting up new plot object.
2025-09-09 15:16:51 runnervmf4ws1 trajan.plot[2509] DEBUG Plotting lines
2025-09-09 15:16:51 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:51 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:51 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:51 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:51 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:51 runnervmf4ws1 trajan.plot[2509] DEBUG Creating new figure and axes..
2025-09-09 15:16:51 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:51 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:51 runnervmf4ws1 trajan.plot[2509] DEBUG Plotting trajectory 0 of 2 with color
2025-09-09 15:16:52 runnervmf4ws1 trajan.plot[2509] DEBUG Plotting trajectory 1 of 2 with color
2025-09-09 15:16:53 runnervmf4ws1 matplotlib.colorbar[2509] DEBUG locator: <matplotlib.ticker.AutoLocator object at 0x7f5e1c1e4b90>
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()

2025-09-09 15:16:53 runnervmf4ws1 trajan.plot[2509] DEBUG Plotting lines
2025-09-09 15:16:53 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:53 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:53 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:53 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:53 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:53 runnervmf4ws1 trajan.plot[2509] DEBUG Creating new figure and axes..
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:54 runnervmf4ws1 trajan.accessor[2509] DEBUG Detecting trajectory dimension
2025-09-09 15:16:54 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected obs-dim: time, detected time-variable: time.
2025-09-09 15:16:54 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected structured (1D) trajectory dataset
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG Setting up new plot object.
2025-09-09 15:16:54 runnervmf4ws1 trajan.plot[2509] DEBUG Plotting lines
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:54 runnervmf4ws1 trajan.plot[2509] DEBUG Axes already exist on existing figure.
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
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()

2025-09-09 15:16:54 runnervmf4ws1 trajan.accessor[2509] DEBUG Detecting trajectory dimension
2025-09-09 15:16:54 runnervmf4ws1 trajan.accessor[2509] DEBUG Single trajectory, a trajectory dimension will be added
2025-09-09 15:16:54 runnervmf4ws1 trajan.accessor[2509] DEBUG Using trajectory_id variable name (drifter_names) as trajectory dimension name
2025-09-09 15:16:54 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected obs-dim: time, detected time-variable: time.
2025-09-09 15:16:54 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected structured (1D) trajectory dataset
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG Setting up new plot object.
2025-09-09 15:16:54 runnervmf4ws1 trajan.plot[2509] DEBUG Plotting lines
2025-09-09 15:16:54 runnervmf4ws1 trajan.accessor[2509] DEBUG Detecting trajectory dimension
2025-09-09 15:16:54 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected obs-dim: time, detected time-variable: time.
2025-09-09 15:16:54 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected structured (1D) trajectory dataset
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:54 runnervmf4ws1 trajan.plot[2509] DEBUG Creating new figure and axes..
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:54 runnervmf4ws1 trajan.accessor[2509] DEBUG Detecting trajectory dimension
2025-09-09 15:16:54 runnervmf4ws1 trajan.accessor[2509] DEBUG Single trajectory, a trajectory dimension will be added
2025-09-09 15:16:54 runnervmf4ws1 trajan.accessor[2509] DEBUG Using trajectory_id variable name (drifter_names) as trajectory dimension name
2025-09-09 15:16:54 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected obs-dim: time, detected time-variable: time.
2025-09-09 15:16:54 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected structured (1D) trajectory dataset
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG Setting up new plot object.
2025-09-09 15:16:54 runnervmf4ws1 trajan.plot[2509] DEBUG Plotting lines
2025-09-09 15:16:54 runnervmf4ws1 trajan.accessor[2509] DEBUG Detecting trajectory dimension
2025-09-09 15:16:54 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected obs-dim: time, detected time-variable: time.
2025-09-09 15:16:54 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected structured (1D) trajectory dataset
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:54 runnervmf4ws1 trajan.plot[2509] DEBUG Axes already exist on existing figure.
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:54 runnervmf4ws1 trajan.traj[2509] 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: 1143)
Coordinates:
* time (time) datetime64[ns] 9kB 2022-10-07 ... 2022-11-23T14:00:00
* trajectory (trajectory) int64 16B 0 1
Data variables:
lon (trajectory, time) float64 18kB nan 29.82 29.77 ... 21.14 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

2025-09-09 15:16:55 runnervmf4ws1 trajan.accessor[2509] DEBUG Detecting trajectory dimension
2025-09-09 15:16:55 runnervmf4ws1 trajan.accessor[2509] DEBUG Single trajectory, a trajectory dimension will be added
2025-09-09 15:16:55 runnervmf4ws1 trajan.accessor[2509] DEBUG Using trajectory_id variable name (drifter_names) as trajectory dimension name
2025-09-09 15:16:55 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected obs-dim: time, detected time-variable: time.
2025-09-09 15:16:55 runnervmf4ws1 trajan.accessor[2509] DEBUG Detected structured (1D) trajectory dataset
Do a basic animation of the drift of the drifters

2025-09-09 15:16:55 runnervmf4ws1 trajan.traj[2509] DEBUG Setting up new animation object.
2025-09-09 15:16:55 runnervmf4ws1 trajan.animation[2509] DEBUG Animating trajectories..
2025-09-09 15:16:55 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:55 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:55 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:55 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:55 runnervmf4ws1 trajan.traj[2509] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
2025-09-09 15:16:55 runnervmf4ws1 trajan.plot[2509] DEBUG Creating new figure and axes..
2025-09-09 15:16:56 runnervmf4ws1 trajan.animation[2509] DEBUG Running animation.. frames: 1143
Total running time of the script: (0 minutes 7.804 seconds)