stac-pydantic

Pydantic models for STAC Catalogs, Collections, Items, and the STAC API spec.

Installation

pip install stac-pydantic

Usage

Loading Models

Load data into models with standard pydantic:

from stac_pydantic import Catalog

stac_catalog = {
  "stac_version": "0.9.0",
  "id": "sample",
  "description": "This is a very basic sample catalog.",
  "links": [
    {
      "href": "item.json",
      "rel": "item"
    }
  ]
}

catalog = Catalog(**stac_catalog)
assert catalog.id == "sample"
assert catalog.links[0].href == "item.json"

Extensions

STAC defines many extensions which let the user customize the data in their catalog. Extensions can be validated implicitly or explicitly:

Implicit

The item_model_factory function creates an appropriate Pydantic model based on the structure of the item by looking at the extensions defined by the stac_extensions member. The model can be created once and reused for the life of the interpreter.

from stac_pydantic import item_model_factory

stac_item = {
    "type": "Feature",
    "stac_extensions": [
        "eo"
    ],
    "geometry": ...,
    "properties": {
        "datetime": "2020-03-09T14:53:23.262208+00:00",
        "eo:gsd": 0.15,
        "eo:cloud_cover": 17
    },
    "links": ...,
    "assets": ...,
}

model = item_model_factory(stac_item)
item = model(**stac_item)

>>> pydantic.error_wrappers.ValidationError: 1 validation error for Item
    __root__ -> properties -> eo:bands
        field required (eo) (type=value_error.missing)

The stac_pydantic.validate_item function provides a convenience wrapper over item_model_factory for one-off validation:

from stac_pydantic import validate_item

assert validate_item(stac_item)

Explicit

Subclass any of the models provided by the library to declare a customized validator:

from stac_pydantic import Item, ItemProperties, Extensions

class CustomProperties(Extensions.view, ItemProperties):
    ...

class CustomItem(Item):
    properties: CustomProperties # Override properties model

stac_item = {
    "type": "Feature",
    "geometry": ...,
    "properties": {
        "datetime": "2020-03-09T14:53:23.262208+00:00",
        "view:off_nadir": 3.78,
    },
    "links": ...,
    "assets": ...,
}

item = CustomItem(**stac_item)
assert item.properties.off_nadir == 3.78

Vendor Extensions

STAC allows 3rd parties to define their own extensions for specific implementations which aren't currently covered by the available content extensions. You can validate vendor extensions in a similar fashion:

from pydantic import BaseModel
from stac_pydantic import Extensions, Item

# 1. Create a model for the extension
class LandsatExtension(BaseModel):
    row: int
    column: int
    
    # Setup extension namespace in model config
    class Config:
        allow_population_by_fieldname = True
        alias_generator = lambda field_name: f"landsat:{field_name}"

# 2. Register the extension
Extensions.register("landsat", LandsatExtension)

# 3. Use model as normal
stac_item = {
    "type": "Feature",
    "stac_extensions": [
        "landsat",
        "view"
],
    "geometry": ...,
    "properties": {
        "datetime": "2020-03-09T14:53:23.262208+00:00",
        "view:off_nadir": 3.78,
        "landsat:row": 230,
        "landsat:column": 178 
    },
    "links": ...,
    "assets": ...,
}

item = Item(**stac_item)
assert item.properties.row == 230
assert item.properties.column == 178

Vendor extensions are often defined in stac_extensions as a remote reference to a JSON schema. When registering extensions, you may use the alias kwarg to indicate that the model represents a specific remote reference:

Extensions.register("landsat", LandsatExtension, alias="https://example.com/stac/landsat-extension/1.0/schema.json")

Exporting Models

Most STAC extensions are namespaced with a colon (ex eo:gsd) to keep them distinct from other extensions. Because Python doesn't support the use of colons in variable names, we use Pydantic aliasing to add the namespace upon model export. This requires exporting the model with the by_alias = True parameter. A convenience method (to_dict()) is provided to export models with extension namespaces:

item_dict = item.to_dict()
assert item_dict['properties']['landsat:row'] == item.properties.row == 250

CLI

Usage: stac-pydantic [OPTIONS] COMMAND [ARGS]...

  stac-pydantic cli group

Options:
  --help  Show this message and exit.

Commands:
  validate-item  Validate STAC Item

Testing

python setup.py test