How to Use the "sel" Parameter for Datasets with >3 Dimensions¶

Datasets with more than the three spatio-temporal dimensions (e.g. x, y, time) will require the use of the sel parameter to pick a particular value of those non-spatio-temporal dimensions. The sel parameter can be used more than once in a given request. The sel parameter can also be used to specify a time within a single granule's data file.

This notebook demonstrates how to get statistics for a single time slice of a granule from the TROPESS O3 dataset, which also includes a fourth dimension lev. This dataset has annual granules each with dimensions for time (monthly). Queries within a single year will return the same granule. If time={datetime} is present in a sel query parameter value, titiler-cmr will pass the datetime query parameter value to the xarray sel parameter for the time dimension.

See also: xarray.DataArray.sel.

Setup¶

In [1]:

import json
import os
from datetime import datetime, timezone

import httpx

titiler_endpoint = os.getenv(
    "TITILER_CMR_ENDPOINT", "https://openveda.cloud/api/titiler-cmr"
)

import json import os from datetime import datetime, timezone import httpx titiler_endpoint = os.getenv( "TITILER_CMR_ENDPOINT", "https://openveda.cloud/api/titiler-cmr" )

In [2]:

geojson_dict = {
    "type": "FeatureCollection",
    "features": [
        {
            "type": "Feature",
            "properties": {},
            "geometry": {
                "coordinates": [
                    [
                        [-20.79973248834736, 83.55979308678764],
                        [-20.79973248834736, 75.0115425216471],
                        [14.483337068956956, 75.0115425216471],
                        [14.483337068956956, 83.55979308678764],
                        [-20.79973248834736, 83.55979308678764],
                    ]
                ],
                "type": "Polygon",
            },
        }
    ],
}

r = httpx.post(
    f"{titiler_endpoint}/xarray/statistics",
    params=(
        ("collection_concept_id", "C2837626477-GES_DISC"),
        # Temporal query for CMR granule query
        ("temporal", datetime(2021, 10, 10, tzinfo=timezone.utc).isoformat()),
        # xarray backend query parameters
        ("variables", "o3"),
        ("sel", "time=nearest::{datetime}"),  #
        ("sel", "lev=1000"),
    ),
    json=geojson_dict,
    timeout=None,
).json()

print(json.dumps(r, indent=2))

geojson_dict = { "type": "FeatureCollection", "features": [ { "type": "Feature", "properties": {}, "geometry": { "coordinates": [ [ [-20.79973248834736, 83.55979308678764], [-20.79973248834736, 75.0115425216471], [14.483337068956956, 75.0115425216471], [14.483337068956956, 83.55979308678764], [-20.79973248834736, 83.55979308678764], ] ], "type": "Polygon", }, } ], } r = httpx.post( f"{titiler_endpoint}/xarray/statistics", params=( ("collection_concept_id", "C2837626477-GES_DISC"), # Temporal query for CMR granule query ("temporal", datetime(2021, 10, 10, tzinfo=timezone.utc).isoformat()), # xarray backend query parameters ("variables", "o3"), ("sel", "time=nearest::{datetime}"), # ("sel", "lev=1000"), ), json=geojson_dict, timeout=None, ).json() print(json.dumps(r, indent=2))

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "geometry": {
        "type": "Polygon",
        "coordinates": [
          [
            [
              -20.79973248834736,
              83.55979308678764
            ],
            [
              -20.79973248834736,
              75.0115425216471
            ],
            [
              14.483337068956956,
              75.0115425216471
            ],
            [
              14.483337068956956,
              83.55979308678764
            ],
            [
              -20.79973248834736,
              83.55979308678764
            ]
          ]
        ]
      },
      "properties": {
        "statistics": {
          "b1": {
            "min": 12.448402404785156,
            "max": 30.638206481933594,
            "mean": 25.00276756286621,
            "count": 236.0,
            "sum": 5900.6533203125,
            "std": 3.4685499803764728,
            "median": 25.134218215942383,
            "majority": 12.448402404785156,
            "minority": 12.448402404785156,
            "unique": 236.0,
            "histogram": [
              [
                2,
                1,
                0,
                6,
                33,
                39,
                37,
                42,
                32,
                44
              ],
              [
                12.448402404785156,
                14.267382621765137,
                16.086362838745117,
                17.905344009399414,
                19.724323272705078,
                21.543304443359375,
                23.362285614013672,
                25.18126678466797,
                27.000246047973633,
                28.81922721862793,
                30.638206481933594
              ]
            ],
            "valid_percent": 95.16,
            "masked_pixels": 12.0,
            "valid_pixels": 236.0,
            "description": "0",
            "percentile_2": 18.29606056213379,
            "percentile_98": 30.242084503173828
          }
        },
        "used_assets": [
          "TRPSCRO3M3D.1:TROPESS_reanalysis_mon_o3_2021.nc"
        ]
      }
    }
  ]
}

You can chose a different time slice from the same granule simply by updating the datetime query parameter.

In [3]:

r = httpx.post(
    f"{titiler_endpoint}/xarray/statistics",
    params=(
        ("collection_concept_id", "C2837626477-GES_DISC"),
        # Datetime for CMR granule query
        ("temporal", datetime(2021, 12, 10, tzinfo=timezone.utc).isoformat()),
        # xarray backend query parameters
        ("variables", "o3"),
        ("sel", "time=nearest::{datetime}"),  #
        ("sel", "lev=1000"),
    ),
    json=geojson_dict,
    timeout=None,
).json()

print(json.dumps(r, indent=2))

r = httpx.post( f"{titiler_endpoint}/xarray/statistics", params=( ("collection_concept_id", "C2837626477-GES_DISC"), # Datetime for CMR granule query ("temporal", datetime(2021, 12, 10, tzinfo=timezone.utc).isoformat()), # xarray backend query parameters ("variables", "o3"), ("sel", "time=nearest::{datetime}"), # ("sel", "lev=1000"), ), json=geojson_dict, timeout=None, ).json() print(json.dumps(r, indent=2))

{
  "detail": "CMR granule search timed out"
}

In [ ]: