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name: reprojection-merge-vrt description: "Routes Rasterio coordinate transforms, reprojection, WarpedVRT, resampling, raster merge, stack, and alignment workflows." disable-model-invocation: true metadata: disco-role: operating license: BSD 3-Clause

Reprojection, Merge, and VRT

Use this sub-skill when a user wants to transform coordinates or geometries, reproject rasters, choose output grid dimensions, normalize rasters with WarpedVRT, merge mosaics, or stack bands.

Typical requests

• "Reproject this GeoTIFF to EPSG:4326."
• "How do I calculate the default output transform?"
• "Merge overlapping rasters with first/last/min/max/sum behavior."
• "Use WarpedVRT to read many sources on the same grid."

What this sub-skill owns

• rasterio.warp.transform, transform_geom, transform_bounds, calculate_default_transform, reproject, and aligned_target.
• rasterio.vrt.WarpedVRT.
• rasterio.merge.merge and rasterio.stack.stack.
• Resampling decisions, source/destination nodata, destination grid sizing, and CRS/bounds validation.

What it excludes

• Basic open/write metadata setup; use dataset-io-profiles if the profile is not understood yet.
• Detailed Window operations; use windows-memory-vsi for window math.
• Geometry extraction/masking; use features-masks before or after reprojection if shapes are involved.
• rio warp, rio merge, and rio stack command flags; use rio-cli for CLI syntax.

Read first

• references/api-reference.md for signatures and parameter relationships.
• references/workflows.md for dataset reprojection, WarpedVRT normalization, and merging patterns.
• references/troubleshooting.md for invalid CRS, bounds/dimensions conflicts, rotated rasters, and RPC/GCP issues.

Helper scripts

• scripts/reproject_to_crs.py — safe local-file reprojection helper using calculate_default_transform and reproject.
• scripts/merge_rasters.py — safe local-file merge helper using rasterio.merge.merge.

Workflow shape

1. Inspect source CRS, transform, bounds, dimensions, band count, dtype, and nodata.
2. Decide whether the task changes only coordinates, only metadata, or the raster grid itself.
3. Use transform, transform_bounds, or transform_geom for coordinate/geometry changes.
4. Use calculate_default_transform and reproject for materialized raster reprojection.
5. Use WarpedVRT when you need a virtual aligned view before reading, merging, or tiling.
6. Use merge for spatial mosaics and stack for band/file stacking.

Decision points

• Use nearest-neighbor resampling for categorical rasters unless the user explicitly wants interpolation.
• Use bilinear/cubic/average only for continuous data where interpolation is meaningful.
• Preserve source nodata explicitly when materializing a reprojected or merged output.
• Reproject or wrap incompatible source grids before merging or stacking.
• Reject rotated, flipped, or upside-down sources for plain merge unless the workflow first normalizes them.

Common mistakes

• Supplying dst_transform without a destination array or dataset.
• Mixing bounds, dimensions, and resolution without one clear grid strategy.
• Merging rasters with different CRS, band count, dtype, or non-rectilinear transforms.
• Losing width, height, CRS, or transform updates when writing the output profile.
• Treating synthetic coordinate checks as proof that a whole dataset reprojected correctly.

Good validation path

• tests/test_warp.py::test_transform
• tests/test_warp.py::test_calculate_default_transform
• tests/test_warp.py::test_reproject_epsg__simple
• tests/test_merge.py::test_merge_method
• tests/test_merge.py::test_merge_warpedvrt

What a future agent should be able to do here

A future agent should be able to answer common reprojection, VRT, merge, and stack questions using only this sub-skill and its bundled files.