Add Skadi package

packages/esssans/docs/index.md

@@ -37,6 +37,11 @@
 
 :::
 
+:::{grid-item-card} SKADI
+:link: user-guide/skadi/index.md
+
+:::
+
 :::{grid-item-card} ISIS instruments
 :link: user-guide/isis/index.md
 

packages/esssans/docs/user-guide/index.md

@@ -7,6 +7,7 @@ maxdepth: 1
 
 installation
 loki/index
+skadi/index
 isis/index
 common/index
 ```

packages/esssans/docs/user-guide/skadi/index.md

@@ -0,0 +1,31 @@
+# SKADI
+
+## Detector diagnostics
+
+::::{grid} 3
+
+:::{grid-item-card} Detector view
+:link: skadi-detector-view.ipynb
+:text-align: center
+
+```{image} ../../_static/thumbnails/skadi_detector_view_light.svg
+:class: only-light
+:width: 100%
+```
+
+```{image} ../../_static/thumbnails/skadi_detector_view_dark.svg
+:class: only-dark
+:width: 100%
+```
+
+:::
+
+::::
+
+```{toctree}
+---
+hidden:
+---
+
+skadi-detector-view
+```

packages/esssans/docs/user-guide/skadi/skadi-detector-view.ipynb

@@ -0,0 +1,74 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "id": "0",
+   "metadata": {},
+   "source": [
+    "# SKADI detector view\n",
+    "\n",
+    "This example uses the SKADI McStas workflow to load detector events and display them in an interactive instrument view. The reduced example file is downloaded on first use and cached by pooch."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "1",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import scippneutron as scn\n",
+    "\n",
+    "from ess.skadi import SkadiMcStasWorkflow\n",
+    "from ess.skadi.data import skadi_mcstas_sample\n",
+    "from ess.sans.types import Filename, RawDetector, SampleRun"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "2",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "workflow = SkadiMcStasWorkflow()\n",
+    "workflow[Filename[SampleRun]] = skadi_mcstas_sample()\n",
+    "detector = workflow.compute(RawDetector[SampleRun])"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "3",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "detector_view = scn.instrument_view(\n",
+    "    detector.bins.sum(), size=0.006, norm=\"log\", cbar=True\n",
+    ")\n",
+    "detector_view"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3 (ipykernel)",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.11.15"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}

packages/esssans/pyproject.toml

@@ -32,6 +32,7 @@ dynamic = ["version"]
 dependencies = [
   "dask>=2022.1.0",
   "graphviz>=0.20",
+  "h5py>=3.11",
   "essreduce>=26.6.0",
   "numpy>=1.26.4",
   "pandas>=2.1.2",

packages/esssans/src/ess/sans/normalization.py

@@ -27,6 +27,7 @@
     Numerator,
     Position,
     ProcessedWavelengthBands,
+    RawDetector,
     ReducedQ,
     ReducedQxQy,
     ReturnEvents,
@@ -90,6 +91,49 @@ def solid_angle(
     )
 
 
+def rectangular_pixel_solid_angle(
+    detector: RawDetector[RunType],
+    sample_position: Position[snx.NXsample, RunType],
+) -> SolidAngle[RunType]:
+    r"""Approximate the solid angle of flat rectangular detector pixels.
+
+    The approximation is :math:`\Delta\Omega = A |\hat{n}\cdot\hat{r}| / r^2`,
+    where :math:`A` is the pixel area, :math:`\hat{n}` is its unit normal, and
+    :math:`r` is the distance from sample to pixel. It is valid when that distance
+    is much larger than the pixel width and height.
+
+    Parameters
+    ----------
+    detector:
+        Detector data with calibrated geometry coordinates: ``position`` contains
+        pixel centers, the x and y components of ``pixel_size`` give the local
+        pixel width and height, and ``detector_normal`` contains dimensionless
+        unit normals. Positions and normals must share a coordinate system with
+        ``sample_position``. Pixel sizes and normals may vary between pixels.
+    sample_position:
+        Position of the sample.
+
+    Returns
+    -------
+    :
+        Solid angles with the detector's pixel coordinates and masks preserved.
+    """
+    scattered_beam = detector.coords['position'] - sample_position
+    pixel_size = detector.coords['pixel_size']
+    area = pixel_size.fields.x * pixel_size.fields.y
+    omega = (
+        area
+        * sc.abs(sc.dot(detector.coords['detector_normal'], scattered_beam))
+        / sc.norm(scattered_beam) ** 3
+    ).to(unit='dimensionless')
+
+    return SolidAngle[RunType](
+        concepts.rewrap_reduced_data(
+            prototype=detector, data=omega, dim=set(detector.dims) - set(omega.dims)
+        )
+    )
+
+
 def mask_solid_angle(
     solid_angle: SolidAngle[RunType],
     masks: DetectorMasks,

packages/esssans/src/ess/skadi/__init__.py

@@ -0,0 +1,24 @@
+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright (c) 2026 Scipp contributors (https://github.com/scipp)
+
+import importlib.metadata
+
+from . import mcstas, workflow
+from .mcstas import load_skadi_mcstas
+from .workflow import SkadiMcStasWorkflow, SkadiWorkflow, skadi_default_parameters
+
+try:
+    __version__ = importlib.metadata.version("esssans")
+except importlib.metadata.PackageNotFoundError:
+    __version__ = "0.0.0"
+
+del importlib
+
+__all__ = [
+    'SkadiMcStasWorkflow',
+    'SkadiWorkflow',
+    'load_skadi_mcstas',
+    'mcstas',
+    'skadi_default_parameters',
+    'workflow',
+]

packages/esssans/src/ess/skadi/data.py

@@ -0,0 +1,25 @@
+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright (c) 2026 Scipp contributors (https://github.com/scipp)
+"""Data for SKADI documentation examples."""
+
+from pathlib import Path
+
+from ess.reduce.data import make_registry
+
+_registry = make_registry(
+    "ess/skadi",
+    files={
+        "skadi_mcstas_1e8_sample10_1_of_50.h5": (
+            "md5:37883335a05c41d420cff2b38f883fc2"
+        ),
+    },
+    version="1",
+)
+
+
+def skadi_mcstas_sample() -> Path:
+    """Return the reduced SKADI McStas sample used in the user guide."""
+    return _registry.get_path("skadi_mcstas_1e8_sample10_1_of_50.h5")
+
+
+__all__ = ["skadi_mcstas_sample"]