Entities

API Documentation

siapy.entities

Entities serve as the foundational data structures in SiaPy, representing key elements of spectral image analysis and processing workflows. They implement consistent, strongly-typed interfaces that allow seamless interaction between spectral data, spatial coordinates, and geometric information.

Module architecture

The relationships between components are shown in the following diagram:

Design principles

SiaPy's architecture follows several key design principles:

Specialized yet compatible: Each entity is optimized for its specific role while maintaining compatibility with the broader SiaPy ecosystem

Independence: Most entities can function independently (with the exception of abstract base classes)

Composition over inheritance:

• The composition is preferred, so that one class can leverage another by injecting it into its architecture
• Inheritance is primarily used to implement common interfaces through base classes

Extensibility:

• The SpectralImage class supports multiple data sources through spectral or rasterio libraries, however, custom data loading can be implemented by creating your own driver
• Basic geometric shapes (e.g. points, lines, polygons) are implemented using the shapely library, which could also be extended through base abstraction

Visual representation of spectral entities

The components follow standard naming conventions for spectral image analysis. A SpectralImage represents a three-dimensional data cube (height × width × bands). Each pixel in this cube has spatial coordinates (x, y) and a corresponding spectral signal with values across all bands.

A signature combines a pixel's spatial location with its spectral signal, creating a complete spatial-spectral data point. The Signatures class serves as a container for multiple such data points, enabling analysis across collections of pixels.

Since spectral images often contain distinct objects with different spectral properties, Shapes (regions of connected pixels) allow for extraction and analysis of specific areas. The SpectralImage class therefore integrates all primitive structures: Pixels and Signals by definition, and Shapes when attached to the image.

Name	What it represents	Shape / size
Spectral image	A single hyperspectral or multispectral data cube.	(H, W, B) → height × width × bands
Spectral image set	An ordered collection of SpectralImage objects. Think of it as a “dataset” with convenience methods that loop internally instead of in user code.	N × SpectralImage for N spectral images
Pixels	One Cartesian coordinate (x, y).	(N, 2) for N pixels
Shapes	A geometric region of interest (e.g. rectangle, polygon, circle), serving as a container of pixels.	Vector geometry
Signatures	A collection of 1-D spectral signals (B,) tied to pixel values (x, y) or aggregated over a shape.	(N, B + 2) → N signatures, each with B spectral bands plus (x, y) coordinates

Pixels

API Documentation

siapy.entities.Pixels

The Pixels class represents spatial coordinates within spectral image, providing a container for (x, y) coordinate pairs. It uses pandas DataFrame internally for storage, enabling high-performance operations. The class provides multiple initialization methods and conversion functions to work with different data representations (i.e. DataFrames, list, arrays)

import numpy as np
import pandas as pd

from siapy.entities import Pixels

# Create from pandas DataFrame
pixels1 = Pixels(pd.DataFrame({"x": [10, 20, 30], "y": [40, 50, 60]}))

# Create from numpy array
pixels2 = Pixels.from_iterable(np.array([[10, 40], [20, 50], [30, 60]]))

# Create from list of coordinates
pixels3 = Pixels.from_iterable([(10, 40), (20, 50), (30, 60)])

# Should be the same
assert pixels1 == pixels2 == pixels3

Signals

API Documentation

siapy.entities.signatures.Signals

The Signals class stores spectral data for each pixel in a pandas DataFrame, allowing you to use any column names you choose (e.g. "band_1", "nir", "red_edge"). You can initialize it from a DataFrame, lists, dicts or NumPy arrays.

from siapy.entities.signatures import Signals

# Create from iterable (e.g. list, array)
signals = Signals.from_iterable([[0.1, 0.2, 0.3], [0.4, 0.5, 0.6]])

However, direct initialization of Signals is typically not necessary in practice. When you create a Signatures instance, the underlying Signals object is automatically generated and managed for you. This section demonstrates the Signals class primarily to illustrate how the Signatures class (discussed next) is composed internally and to provide insight into the data structure that powers spectral analysis.

Signatures

API Documentation

siapy.entities.Signatures

The Signatures class represents spectral data collections by combining spatial coordinates (Pixels) with their corresponding spectral values (Signals). It provides a unified container that maintains the spatial-spectral relationship, allowing for analysis of spectral information at specific image locations. Internally, the data is stored as pandas DataFrames for efficient operations and indexing.

Signatures can be initialized in multiple ways. The explicit approach creates each component separately before combining them, providing clarity about the composition:

import pandas as pd
from rich import print

from siapy.entities import Pixels, Signatures
from siapy.entities.signatures import Signals

# Option 1: Step-by-step initialization
# Initialize Pixels object from a DataFrame
pixels_df = pd.DataFrame({"x": [10, 30], "y": [20, 40]})
pixels = Pixels(pixels_df)

# Initialize Signals object from a DataFrame
signals_df = pd.DataFrame([[1, 2, 3], [4, 5, 6]])
signals = Signals(signals_df)

# Create Signatures object from Pixels and Signals objects
signatures1 = Signatures(pixels, signals)

For more concise code, you can initialize a Signatures object directly from coordinate and signal values:

# Option 2: Direct initialization with raw data
# Initialize Signatures directly from raw signals and coordinates data
signatures2 = Signatures.from_signals_and_pixels(
    signals=[[1, 2, 3], [4, 5, 6]],
    pixels=[[10, 20], [30, 40]],
)

Both approaches yield equivalent results when initialized with the same data. You can access and work with the data using various DataFrame operations and conversion methods:

# Verify that both approaches produce equivalent results
assert signatures1 == signatures2

# Print the DataFrame representation of Pixels and Signals
df_multi = signatures2.to_dataframe_multiindex()
print(f"MultiIndex DataFrame:\n{df_multi}")
print(f"Signals DataFrame:\n{signatures2.signals.df}")
print(f"Pixels DataFrame:\n{signatures2.pixels.df}")

Shape

API Documentation

siapy.entities.Shape

The Shape class represents geometric shapes that can be associated with images, such as points, lines, and polygons.

from siapy.entities import Pixels, Shape

# Create a point
point = Shape.from_point(10, 20)

# Create a polygon from pixels
pixels = Pixels.from_iterable([(0, 0), (10, 0), (10, 10), (0, 10)])
polygon = Shape.from_polygon(pixels)

# Load from shapefile
shape = Shape.open_shapefile("path/to/shapefile.shp")

Spectral Image

API Documentation

siapy.entities.SpectralImage

A SpectralImage is the primary container for spectral image data. It's a generic class that can wrap different image backends, allowing you to work with various file formats through a unified interface.

Image Initialization Options

1. Load from ENVI format (using spectral python)

This is commonly used for hyperspectral imagery from airborne or satellite sensors.

from siapy.entities import SpectralImage
from siapy.entities.images import SpectralLibImage

# Load from ENVI format (uses spectral python library)
image_sp = SpectralLibImage.open(
    header_path="path/to/header.hdr",
    image_path="path/to/image.img",
)
image = SpectralImage(image_sp)

# Or you can use the class method to load the image directly
image = SpectralImage.spy_open(
    header_path="path/to/header.hdr",
    image_path="path/to/image.img",
)

2. Load from GeoTIFF or other geospatial formats (using rasterio)

Perfect for georeferenced data with spatial information.

from siapy.entities import SpectralImage
from siapy.entities.images import RasterioLibImage

# Load from GeoTIFF or other raster formats (uses rioxarray/rasterio python library)
image_rio = RasterioLibImage.open(
    filepath="path/to/image.tif",
)
image = SpectralImage(image_rio)

# Or you can use the class method to load the image directly
image = SpectralImage.rasterio_open(filepath="path/to/image.tif")

3. Create from numpy array

Useful for testing or when you already have image data in memory.

import numpy as np

from siapy.entities import SpectralImage

# Create a SpectralImage from a numpy array - mostly for testing
array = np.zeros((100, 100, 10))  # height, width, bands
image = SpectralImage.from_numpy(array)

4. Create your own custom image class

For specialized file formats or custom processing needs, you can extend the ImageBase class.

from pathlib import Path
from typing import TYPE_CHECKING, Any, cast

import numpy as np
import xarray as xr
from numpy.typing import NDArray
from PIL import Image

from siapy.core.exceptions import InvalidFilepathError
from siapy.entities import SpectralImage
from siapy.entities.images import ImageBase

if TYPE_CHECKING:
    from siapy.core.types import XarrayType


class MyImage(ImageBase):
    """
    # Create your own image class by extending ImageBase
    # This example demonstrates how to implement a custom image loader
    """

    def __init__(self, data: NDArray[np.floating[Any]], file_path: Path) -> None:
        self._data = data
        self._filepath = file_path

        # Define metadata with required fields:
        # - camera_id: unique identifier for the imaging device
        # - wavelengths: list of spectral band centers in nanometers
        # - default_bands: which bands to use for RGB visualization
        self._meta: dict[str, Any] = {
            "camera_id": "my_camera",
            "wavelengths": [450.0, 550.0, 650.0],  # RGB wavelengths in nm
            "default_bands": [0, 1, 2],  # Band indices for RGB display
        }

    @classmethod
    def open(cls, filepath: str) -> "MyImage":
        """Load an image from a file path"""
        path = Path(filepath)
        if not path.exists():
            raise InvalidFilepathError(f"File not found: {filepath}")

        try:
            # This is a simplified example - in a real implementation,
            # you would read the actual image data using an appropriate library
            # For example purposes, creating a small random array
            data = np.random.random((100, 100, 3)).astype(np.float32)
            return cls(data, path)
        except Exception as e:
            raise InvalidFilepathError(f"Failed to open {filepath}: {str(e)}")

    # Required properties (all must be implemented)

    @property
    def filepath(self) -> Path:
        """Path to the source file"""
        return self._filepath

    @property
    def metadata(self) -> dict[str, Any]:
        """Image metadata dictionary"""
        return self._meta

    @property
    def shape(self) -> tuple[int, int, int]:
        """Image dimensions as (height, width, bands)"""
        return cast(tuple[int, int, int], self._data.shape)

    @property
    def bands(self) -> int:
        """Number of spectral bands"""
        return self.shape[2]

    @property
    def default_bands(self) -> list[int]:
        """Indices of bands to use for RGB visualization"""
        return self._meta["default_bands"]

    @property
    def wavelengths(self) -> list[float]:
        """Center wavelengths of each band in nanometers"""
        return self._meta["wavelengths"]

    @property
    def camera_id(self) -> str:
        """Unique identifier for the imaging device"""
        return self._meta["camera_id"]

    # Required methods (all must be implemented)

    def to_display(self, equalize: bool = True) -> Image.Image:
        """Convert to PIL Image for display"""
        # Extract the default bands for RGB visualization
        rgb_data = self._data[:, :, self.default_bands].copy()

        if equalize:
            # Apply linear contrast stretching to each band
            for i in range(rgb_data.shape[2]):
                band = rgb_data[:, :, i]
                min_val = np.min(band)
                max_val = np.max(band)
                if max_val > min_val:
                    rgb_data[:, :, i] = (band - min_val) / (max_val - min_val)

        # Convert to 8-bit for PIL
        rgb_uint8 = (rgb_data * 255).astype(np.uint8)
        return Image.fromarray(rgb_uint8)

    def to_numpy(self, nan_value: float | None = None) -> NDArray[np.floating[Any]]:
        """Convert to numpy array"""
        result = self._data.copy()
        if nan_value is not None:
            result[np.isnan(result)] = nan_value
        return result

    def to_xarray(self) -> "XarrayType":
        """Convert to xarray DataArray with coordinates"""
        return xr.DataArray(
            self._data,
            dims=["y", "x", "band"],
            coords={
                "y": np.arange(self.shape[0]),
                "x": np.arange(self.shape[1]),
                "band": self.wavelengths,
            },
            attrs=self.metadata,
        )


# Example: Using your custom image class with SiaPy
# 1. Create an instance of your custom image class
custom_image = MyImage.open("path/to/your/image.dat")

# 2. Wrap it in a SpectralImage for use with SiaPy's analysis tools
spectral_image = SpectralImage(custom_image)

# 3. Now you can use all SiaPy functionality
# spectral_image.to_signatures(pixels)
# etc.

Data conversion methods

The example below demonstrates two key conversion methods of SpectralImage instance:

1. to_signatures(): Extracts spectral data from specific pixel coordinates and returns a Signatures object that maintains the spatial-spectral relationship
2. to_subarray(): Converts selected pixel data to a NumPy array for numerical processing or integration with other scientific libraries

import numpy as np
from rich import print

from siapy.entities import Pixels, SpectralImage

# Create mock image
rng = np.random.default_rng(seed=42)
array = rng.random((100, 100, 10))  # height, width, bands
image = SpectralImage.from_numpy(array)

# Define pixels
iterable = [(1, 2), (3, 4), (2, 4)]
pixels = Pixels.from_iterable(iterable)

# Get signatures
signatures = image.to_signatures(pixels)
print(f"Signatures:\n{signatures}")

# Get numpy array
subarray = image.to_subarray(pixels)
print(f"Subarray:\n{subarray}")
"""
? Note:
    The extracted block has shape (3, 3, 10): a 3 × 3 pixel window across 10 spectral bands.
    Values are populated only at the requested pixel coordinates; all other elements are set to NaN.
"""

Manipulation of Shapes

Each SpectralImage instance automatically initializes a GeometricShapes object as a property called geometric_shapes. This property provides a container for managing shape objects associated with the image. It lets you work with image regions while maintaining the connection between spatial geometries and their spectral data. This is particularly useful for region-based analysis, masking, and feature extraction from specific areas of interest.

The GeometricShapes class provides a list-like interface that wraps a standard Python list, enhancing it with specialized functionality for manipulating geometric shapes while preserving standard list behavior. The list of shapes can be accessed via the image.geometric_shapes.shapes property.

import numpy as np
from rich import print

from siapy.entities import Shape, SpectralImage
from siapy.entities.shapes import GeometricShapes

# Create a mock spectral image
rng = np.random.default_rng(seed=42)
array = rng.random((100, 100, 10))  # height, width, bands
image = SpectralImage.from_numpy(array)

# SpectralImage automatically initializes GeometricShapes
assert isinstance(image.geometric_shapes, GeometricShapes)
# You can access the underlying list via the shapes property
assert isinstance(image.geometric_shapes.shapes, list)

# GeometricShapes implements common list operations directly, i.e. number of shapes:
length_via_geometric_shapes = len(image.geometric_shapes)
length_via_raw_list = len(image.geometric_shapes.shapes)

As a result, shapes can be added to the spectral image using standard list operations. The example below demonstrates how this can be done:

# Create two Shape objects with distinct spatial coordinates and semantic labels
coords1 = [(1, 2), (3, 4), (2, 4)]
shape1 = Shape.from_multipoint(coords1, label="coords1")
coords2 = [(19, 20), (21, 22), (20, 22)]
shape2 = Shape.from_multipoint(coords2, label="coords2")

# Add multiple shapes to the SpectralImage's geometric_shapes container at once
image.geometric_shapes.extend([shape1, shape2])

# Display the current collection of shapes stored in the image
# Each shape will be shown with its type and label
print(f"Shapes in GeometricShapes: {image.geometric_shapes}")

Spectral Image Set

API Documentation

siapy.entities.SpectralImageSet

The SpectralImageSet class manages a collection of spectral images.

from pathlib import Path

from siapy.entities import SpectralImageSet

# Load multiple images
header_paths = list(Path("data_dir").glob("*.hdr"))
image_paths = list(Path("data_dir").glob("*.img"))
image_set = SpectralImageSet.spy_open(header_paths=header_paths, image_paths=image_paths)

# Iterate over the images
for image in image_set:
    print(image)