.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "gallery/example_model_along_trajectory.py"
.. LINE NUMBERS ARE GIVEN BELOW.

.. only:: html

    .. note::
        :class: sphx-glr-download-link-note

        :ref:`Go to the end <sphx_glr_download_gallery_example_model_along_trajectory.py>`
        to download the full example code.

.. rst-class:: sphx-glr-example-title

.. _sphx_glr_gallery_example_model_along_trajectory.py:


Read variables from a model along the trajectories of drifters.
=============================================================================

.. GENERATED FROM PYTHON SOURCE LINES 5-15

.. code-block:: Python


    import xarray as xr
    import numpy as np
    import cf_xarray as _
    import pyproj
    import trajan as ta
    import matplotlib.pyplot as plt

    print(ta.versions())





.. rst-class:: sphx-glr-script-out

 .. code-block:: none


    ------------------------------------------------------
    Software and hardware:
      TrajAn version 0.8.0
      Platform: Linux, 6.11.0-1018-azure
      15.615982055664062 GB memory
      4 processors (x86_64)
      NumPy version 2.4.2
      SciPy version 1.17.0
      Matplotlib version 3.10.8
      NetCDF4 version 1.7.4
      Xarray version 2025.9.0
      Pandas version 3.0.1
      OpenDrift version 1.14.8
      Python version 3.14.3 | packaged by conda-forge | (main, Feb  9 2026, 21:56:02) [GCC 14.3.0]
    ------------------------------------------------------





.. GENERATED FROM PYTHON SOURCE LINES 16-17

Open drifter dataset from a CSV file

.. GENERATED FROM PYTHON SOURCE LINES 17-24

.. code-block:: Python

    ds = ta.read_csv('bug05_pos.csv.xz',
                     lon='Longitude',
                     lat='Latitude',
                     time='Time',
                     name='Device')
    print(ds)





.. rst-class:: sphx-glr-script-out

 .. code-block:: none

    2026-02-22 07:38:28 runnervmwffz4 trajan.accessor[3928] DEBUG Detecting trajectory dimension
    2026-02-22 07:38:28 runnervmwffz4 trajan.accessor[3928] DEBUG No trajectory_id attribute/variable found, trying to identify by name.
    2026-02-22 07:38:28 runnervmwffz4 trajan.accessor[3928] DEBUG Detecting time-variable for "obs"..
    2026-02-22 07:38:28 runnervmwffz4 trajan.accessor[3928] DEBUG Detected obs-dim: obs, detected time-variable: time.
    2026-02-22 07:38:28 runnervmwffz4 trajan.accessor[3928] DEBUG Detected un-structured (2D) trajectory dataset
    2026-02-22 07:38:28 runnervmwffz4 trajan.traj2d[3928] DEBUG Condensing 844 observations.
    2026-02-22 07:38:28 runnervmwffz4 trajan.traj2d[3928] DEBUG Condensed observations from: 844 to 844
    2026-02-22 07:38:28 runnervmwffz4 trajan.accessor[3928] DEBUG Detecting trajectory dimension
    2026-02-22 07:38:28 runnervmwffz4 trajan.accessor[3928] DEBUG No trajectory_id attribute/variable found, trying to identify by name.
    2026-02-22 07:38:28 runnervmwffz4 trajan.accessor[3928] DEBUG Detecting time-variable for "obs"..
    2026-02-22 07:38:28 runnervmwffz4 trajan.accessor[3928] DEBUG Detected obs-dim: obs, detected time-variable: time.
    2026-02-22 07:38:28 runnervmwffz4 trajan.accessor[3928] DEBUG Detected un-structured (2D) trajectory dataset
    2026-02-22 07:38:28 runnervmwffz4 trajan.traj[3928] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
    2026-02-22 07:38:28 runnervmwffz4 trajan.traj[3928] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
    2026-02-22 07:38:28 runnervmwffz4 trajan.traj[3928] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
    2026-02-22 07:38:28 runnervmwffz4 trajan.traj[3928] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
    <xarray.Dataset> Size: 27kB
    Dimensions:     (trajectory: 1, obs: 844)
    Coordinates:
      * trajectory  (trajectory) <U18 72B 'dev864475040536665'
      * obs         (obs) int64 7kB 0 1 2 3 4 5 6 7 ... 837 838 839 840 841 842 843
    Data variables:
        time        (trajectory, obs) datetime64[us] 7kB 2022-05-10T12:56:16.5000...
        lon         (trajectory, obs) float64 7kB 5.332 5.332 5.332 ... 5.25 5.25
        lat         (trajectory, obs) float64 7kB 60.38 60.38 60.38 ... 60.45 60.45
    Attributes:
        Conventions:          CF-1.10
        featureType:          trajectory
        geospatial_lat_min:   60.38380600000001
        geospatial_lat_max:   60.45141000000001
        geospatial_lon_min:   5.244493666666667
        geospatial_lon_max:   5.33242
        time_coverage_start:  2020-01-01T00:00:07.250000
        time_coverage_end:    2022-05-20T11:03:46.120000




.. GENERATED FROM PYTHON SOURCE LINES 25-26

Open the Norkyst800 model

.. GENERATED FROM PYTHON SOURCE LINES 26-29

.. code-block:: Python

    nk = xr.open_dataset(
        'https://thredds.met.no/thredds/dodsC/sea/norkyst800m/1h/aggregate_be')








.. GENERATED FROM PYTHON SOURCE LINES 30-31

Use cf-xarray to get the CRS

.. GENERATED FROM PYTHON SOURCE LINES 31-35

.. code-block:: Python

    gm = nk.cf['grid_mapping']
    nk_crs = pyproj.CRS.from_cf(gm.attrs)
    print(nk_crs)





.. rst-class:: sphx-glr-script-out

 .. code-block:: none

    2026-02-22 07:39:42 runnervmwffz4 pyproj[3928] DEBUG PROJ_ERROR: proj_create: several objects matching this name: Krovak (Greenwich), Equal Earth Greenwich, Laborde Grid (Greenwich), Modified Krovak (Greenwich), Krovak East North (Greenwich), Modified Krovak East North (Greenwich), ...
    {"$schema": "https://proj.org/schemas/v0.2/projjson.schema.json", "type": "ProjectedCRS", "name": "undefined", "base_crs": {"$schema": "https://proj.org/schemas/v0.7/projjson.schema.json", "type": "GeographicCRS", "name": "undefined", "datum": {"type": "GeodeticReferenceFrame", "name": "undefined", "ellipsoid": {"name": "undefined", "semi_major_axis": 6378137, "semi_minor_axis": 6356752.3142}}, "coordinate_system": {"subtype": "ellipsoidal", "axis": [{"name": "Longitude", "abbreviation": "lon", "direction": "east", "unit": "degree"}, {"name": "Latitude", "abbreviation": "lat", "direction": "north", "unit": "degree"}]}}, "conversion": {"$schema": "https://proj.org/schemas/v0.7/projjson.schema.json", "type": "Conversion", "name": "unknown", "method": {"name": "Polar Stereographic (variant B)", "id": {"authority": "EPSG", "code": 9829}}, "parameters": [{"name": "Latitude of standard parallel", "value": 60, "unit": "degree", "id": {"authority": "EPSG", "code": 8832}}, {"name": "Longitude of origin", "value": 70, "unit": "degree", "id": {"authority": "EPSG", "code": 8833}}, {"name": "False easting", "value": 3192800, "unit": "metre", "id": {"authority": "EPSG", "code": 8806}}, {"name": "False northing", "value": 1784000, "unit": "metre", "id": {"authority": "EPSG", "code": 8807}}]}, "coordinate_system": {"$schema": "https://proj.org/schemas/v0.7/projjson.schema.json", "type": "CoordinateSystem", "subtype": "Cartesian", "axis": [{"name": "Easting", "abbreviation": "E", "direction": "east", "unit": "metre"}, {"name": "Northing", "abbreviation": "N", "direction": "north", "unit": "metre"}]}}




.. GENERATED FROM PYTHON SOURCE LINES 36-37

Grid the drifter dataset to the timesteps of the model.

.. GENERATED FROM PYTHON SOURCE LINES 37-43

.. code-block:: Python

    times = nk.sel(time=slice('2022-05-10', '2022-05-20')).time.values
    ds = ds.traj.gridtime(times)
    ds = ds.dropna('time', how='all')

    print(ds)





.. rst-class:: sphx-glr-script-out

 .. code-block:: none

    2026-02-22 07:39:42 runnervmwffz4 trajan.accessor[3928] DEBUG Detecting trajectory dimension
    2026-02-22 07:39:42 runnervmwffz4 trajan.accessor[3928] DEBUG Detecting time-variable for "obs"..
    2026-02-22 07:39:42 runnervmwffz4 trajan.accessor[3928] DEBUG Detected obs-dim: obs, detected time-variable: time.
    2026-02-22 07:39:42 runnervmwffz4 trajan.accessor[3928] DEBUG Detected un-structured (2D) trajectory dataset
    2026-02-22 07:39:42 runnervmwffz4 trajan.accessor[3928] DEBUG Detecting trajectory dimension
    2026-02-22 07:39:42 runnervmwffz4 trajan.accessor[3928] DEBUG Detecting time-variable for "obs"..
    2026-02-22 07:39:42 runnervmwffz4 trajan.accessor[3928] DEBUG Detected obs-dim: obs, detected time-variable: time.
    2026-02-22 07:39:42 runnervmwffz4 trajan.accessor[3928] DEBUG Detected un-structured (2D) trajectory dataset
    2026-02-22 07:39:42 runnervmwffz4 trajan.accessor[3928] DEBUG Detecting trajectory dimension
    2026-02-22 07:39:42 runnervmwffz4 trajan.accessor[3928] DEBUG Detected obs-dim: time, detected time-variable: time.
    2026-02-22 07:39:42 runnervmwffz4 trajan.accessor[3928] DEBUG Detected structured (1D) trajectory dataset
    2026-02-22 07:39:42 runnervmwffz4 trajan.traj1d[3928] WARNING non-unique time points, dropping time-duplicates
    <xarray.Dataset> Size: 6kB
    Dimensions:     (trajectory: 1, time: 239)
    Coordinates:
      * time        (time) datetime64[us] 2kB 2022-05-10T13:00:00 ... 2022-05-20T...
      * trajectory  (trajectory) <U18 72B 'dev864475040536665'
    Data variables:
        lon         (trajectory, time) float64 2kB 5.332 5.332 5.332 ... 5.249 5.25
        lat         (trajectory, time) float64 2kB 60.38 60.38 60.38 ... 60.44 60.45
    Attributes:
        Conventions:          CF-1.10
        featureType:          trajectory
        geospatial_lat_min:   60.38380600000001
        geospatial_lat_max:   60.45141000000001
        geospatial_lon_min:   5.244493666666667
        geospatial_lon_max:   5.33242
        time_coverage_start:  2020-01-01T00:00:07.250000
        time_coverage_end:    2022-05-20T11:03:46.120000




.. GENERATED FROM PYTHON SOURCE LINES 44-45

Transform the drifter dataset to the CRS of the model

.. GENERATED FROM PYTHON SOURCE LINES 45-48

.. code-block:: Python

    dst = ds.traj.transform(nk_crs)
    print(dst.x)





.. rst-class:: sphx-glr-script-out

 .. code-block:: none

    2026-02-22 07:39:42 runnervmwffz4 trajan.accessor[3928] DEBUG Detecting trajectory dimension
    2026-02-22 07:39:42 runnervmwffz4 trajan.accessor[3928] DEBUG Detected obs-dim: time, detected time-variable: time.
    2026-02-22 07:39:42 runnervmwffz4 trajan.accessor[3928] DEBUG Detected structured (1D) trajectory dataset
    2026-02-22 07:39:42 runnervmwffz4 trajan.traj[3928] DEBUG No grid-mapping specified, checking if coordinates are lon/lat..
    2026-02-22 07:39:42 runnervmwffz4 trajan.accessor[3928] DEBUG Detecting trajectory dimension
    2026-02-22 07:39:42 runnervmwffz4 trajan.accessor[3928] DEBUG Detected obs-dim: time, detected time-variable: time.
    2026-02-22 07:39:42 runnervmwffz4 trajan.accessor[3928] DEBUG Detected structured (1D) trajectory dataset
    <xarray.DataArray 'x' (trajectory: 1, time: 239)> Size: 2kB
    array([[341742.63684573, 341746.32710342, 341750.58095892,
            341754.83482578, 341759.08870403, 341763.34259365,
            341767.59649465, 341771.85040703, 341776.10433078,
            341780.35826591, 341784.61221241, 341788.86617029,
            341793.12013955, 341797.37412018, 341801.62811219,
            341805.88211558, 341810.13613034, 341814.39015647,
            341818.64419399, 341822.89824288, 341827.15230314,
            341831.40637478, 341835.6604578 , 341839.91455219,
            341844.16865796, 341848.42277511, 341852.67690363,
            341856.93104353, 341861.1851948 , 341865.43935745,
            341869.69353147, 341873.94771687, 341878.20191364,
            341882.45612179, 341886.71034132, 341890.96457222,
            341895.2188145 , 341899.47306815, 341903.72733318,
            341907.98160959, 341912.23589736, 341916.49019652,
            341920.74450705, 341924.99882895, 341929.25316223,
            341933.50750689, 341937.76186292, 341942.01623033,
            341946.27060911, 341950.52499926, 341954.7794008 ,
            341959.0338137 , 341963.28823798, 341967.54267364,
            341971.79712067, 341976.05157908, 341980.30604886,
            341984.56053002, 341988.81502255, 341993.06952645,
    ...
            342507.94844798, 342512.2043394 , 342516.46024219,
            342520.71615635, 342524.97208188, 342529.22801879,
            342533.48396706, 342537.7399267 , 342541.99589772,
            342546.25188011, 342550.50787387, 342554.763879  ,
            342559.0198955 , 342563.27592337, 342567.53196261,
            342571.78801322, 342576.0440752 , 342580.30014856,
            342584.55623328, 342588.81232938, 342593.06843685,
            342597.32455568, 342601.58068589, 342605.83682747,
            342610.09298042, 342614.34914474, 342618.60532043,
            342622.86150749, 342627.11770592, 342631.37391573,
            342635.6301369 , 342639.88636944, 342644.14261335,
            342648.39886864, 342652.65513529, 342656.91141331,
            342661.16770271, 342665.42400347, 342669.68031561,
            342673.93663911, 342678.19297399, 342682.44932023,
            342686.70567785, 342690.96204683, 342695.21842719,
            342699.47481891, 342703.73122201, 342707.98763647,
            342712.24406231, 342716.50049951, 342720.75694809,
            342725.01340803, 342729.26987935, 342733.52636203,
            342743.94356181, 346363.11391299, 345860.07469316,
            345775.39990869, 346050.77654721]])
    Coordinates:
      * time        (time) datetime64[us] 2kB 2022-05-10T13:00:00 ... 2022-05-20T...
      * trajectory  (trajectory) <U18 72B 'dev864475040536665'
    Attributes:
        grid_mapping:  polar_stereographic




.. GENERATED FROM PYTHON SOURCE LINES 49-50

Extract the values of a variable for the trajectory

.. GENERATED FROM PYTHON SOURCE LINES 50-56

.. code-block:: Python

    temp = nk.isel(depth=0).sel(time=dst.time,
                                X=dst.x,
                                Y=dst.y,
                                method='nearest').temperature
    print(temp)





.. rst-class:: sphx-glr-script-out

 .. code-block:: none

    <xarray.DataArray 'temperature' (time: 239, trajectory: 1)> Size: 956B
    [239 values with dtype=float32]
    Coordinates:
        X           (trajectory, time) float64 2kB 3.416e+05 3.416e+05 ... 3.464e+05
        Y           (trajectory, time) float64 2kB 4.344e+05 4.344e+05 ... 4.416e+05
        depth       float64 8B 0.0
      * time        (time) datetime64[ns] 2kB 2022-05-10T13:00:00 ... 2022-05-20T...
        lat         (trajectory, time) float64 2kB ...
        lon         (trajectory, time) float64 2kB ...
      * trajectory  (trajectory) <U18 72B 'dev864475040536665'
    Attributes:
        units:          Celsius
        time:           ocean_time
        grid:           grid
        location:       face
        field:          temperature, scalar, series
        grid_mapping:   projection_stere
        long_name:      Sea water potential temperature
        standard_name:  sea_water_potential_temperature
        _ChunkSizes:    [   1    1   17 2602]




.. GENERATED FROM PYTHON SOURCE LINES 57-58

Notice that the `lat` and `lon` variables from Norkyst match the original `lat` and `lon` from the dataset.

.. GENERATED FROM PYTHON SOURCE LINES 58-62

.. code-block:: Python


    plt.figure()
    temp.plot()
    plt.show()



.. image-sg:: /gallery/images/sphx_glr_example_model_along_trajectory_001.png
   :alt: depth = 0.0 [m], trajectory = dev864475040536665
   :srcset: /gallery/images/sphx_glr_example_model_along_trajectory_001.png
   :class: sphx-glr-single-img






.. rst-class:: sphx-glr-timing

   **Total running time of the script:** (1 minutes 50.819 seconds)


.. _sphx_glr_download_gallery_example_model_along_trajectory.py:

.. only:: html

  .. container:: sphx-glr-footer sphx-glr-footer-example

    .. container:: sphx-glr-download sphx-glr-download-jupyter

      :download:`Download Jupyter notebook: example_model_along_trajectory.ipynb <example_model_along_trajectory.ipynb>`

    .. container:: sphx-glr-download sphx-glr-download-python

      :download:`Download Python source code: example_model_along_trajectory.py <example_model_along_trajectory.py>`

    .. container:: sphx-glr-download sphx-glr-download-zip

      :download:`Download zipped: example_model_along_trajectory.zip <example_model_along_trajectory.zip>`


.. only:: html

 .. rst-class:: sphx-glr-signature

    `Gallery generated by Sphinx-Gallery <https://sphinx-gallery.github.io>`_