QGIS Processing

QGIS Processing

When To Use

• Use when the request explicitly mentions QGIS, qgis_process, or Processing algorithms.
• Use when a map layer needs a QGIS algorithm such as buffer, clip, dissolve, extract, field calculation, reprojection, or layout export.
• Use when a multi-step workflow needs chained QGIS outputs instead of a single one-off run.

Workflow

1. List map layers first when the user refers to a layer already on the map.
2. Use integrationInputs.qgis.inputPath from the layer listing when available. Fall back to localFilePath only for file-backed layers.
3. Search algorithms with qgis_list_algorithms using a focused query, an optional provider, and a small limit. Prefer provider: native first. For compound tasks, search the immediate step you need next instead of the whole workflow at once.
4. Describe the shortlisted algorithm with qgis_describe_algorithm before building parameters.
5. Run the algorithm with qgis_run_processing using the exact parameter names from the description.
6. For final outputs, use a simple named file such as buffer.geojson, result.gpkg, or warped.tif and let Arion manage the output workspace.
7. Chain multi-step workflows by feeding returned artifact paths into the next QGIS run.
8. After each run, inspect result, artifacts, and importedLayers before deciding the next step.

Guardrails

• Do not guess algorithm ids from memory when qgis_list_algorithms and qgis_describe_algorithm can confirm them.
• Do not use arbitrary absolute output paths for generated files unless they are already inside Arion's managed QGIS workspace. Prefer relative output filenames.
• Do not rely on TEMPORARY_OUTPUT for a final result that should appear on the map. Use a named output file instead.
• Prefer approved native:* algorithms. Treat non-native algorithms as suspect until the tool response confirms they are allowed.
• For feature-inspection tasks, prefer extraction or transformation workflows that produce a concrete vector or table output the app can import and preview.

Search Hints

• Search buffer, clip, dissolve, reproject, extract, field, order, sort, geometry, layout, translate, or warp instead of requesting the full algorithm catalog.
• If the first search is too broad, narrow by provider or add a second keyword such as extract expression or field calculator.
• For requests like top 10 longest lines, search sort line features by length or order by expression first, then search the extraction or retention step separately.