Capabilities and limits

The packages provide browser-based georeferencing of ordinary images. They implement the raster-georeferencer workflow, with optional geographic digitizing. They do not reproduce every format, projection resource or desktop integration available in a native QGIS/GDAL installation.

Transformations and coordinates

Count alone does not establish validity. Rank, conditioning, duplicates, projective poles and sampled nonlinear domains are checked. Sampled domain checks cannot prove global invertibility; extreme distortions may be rejected conservatively.

The compatibility baseline is QGIS 3.44.0, GDAL 3.8.4 and PROJ 9.4.0. The product requires three noncollinear TPS points even though QGIS's low-level transformer accepts one/two-point special cases. Linear uses QGIS's absolute-scale convention. Polynomial backward mappings are independently fitted reverse polynomials, not exact mathematical inverses; TPS uses a Newton inverse and Projective an analytical inverse. Preview and export use the same fitted model and backward mapping.

Residuals use r = T(image) - target and RMSE = sqrt(sum(||r||²) / enabledCount) in the working CRS. Training residuals are not independent accuracy estimates or a claim to reproduce QGIS's UI RMS. Image coordinates use original-resolution normalized pixels, top-left corner origin and downward Y; the first pixel centre is (0.5, 0.5).

Images, output and resource budgets

• Inputs: ordinary 8-bit nonanimated PNG, grayscale/RGB JPEG, static WebP and single-page, orientation-1, chunky uint8 grayscale/RGB/unassociated-RGBA TIFF. Supported TIFF compression is none, LZW, Deflate and PackBits. PNG/JPEG/WebP normalize all eight EXIF orientations. Unsupported layouts fail explicitly.
• Defaults: 25 MiB compressed input, 24 million input/output pixels, 128 enabled GCPs, 768-pixel preview edge and 768 MiB estimated processing reservation. Full-resolution buffers still exist. The reservation is not a process-memory cap; browsers can require substantially more memory. Deflate reserves extra working space and can reduce the output size accepted under the same budget.
• Optional GeoTIFF: uint8 RGBA with alpha or RGB with numeric no-data, strip-based none/Deflate/PackBits compression and supported horizontal prediction. Numeric no-data cannot preserve partial alpha. COG, scientific/multiband preservation, multipage output and arbitrary TIFF creation options are unsupported.
• Resampling: nearest, bilinear, cubic, cubic spline and Lanczos. Source positions use 1e-9-pixel precision to stabilize floating-point ties. Files need not be byte-identical to GDAL output to have equivalent coordinates and pixels.
• JPEG exports require their world-file/CRS sidecars for placement. Original-pixel world-file-only output is limited to Linear/Helmert without reprojection.
• GeoTIFF output EPSG codes must be below 32767; arbitrary-WKT tagging is not supported. Custom working CRSs can be reprojected to a supported output CRS.
• PDF reports support aligned rasters and optional loaded canvas map layers with valid CORS. WebGL/custom map renderers need a host adapter. PDF cancellation discards the result but cannot interrupt synchronous PDF generation.

Integration boundaries

The host supplies projection definitions and required NTv2 grids, reference authentication and persistence. There is no automatic datum-grid download. Antimeridian/wrapped extents and geometries are rejected; hosts can split reference queries in a custom loader. Drawing uses Point, LineString and Polygon; existing holes are preserved, but dedicated hole creation and multipart editing are not built-in tools. Desktop Chromium, Firefox and WebKit are the automated browser targets; WebKit testing is not a separate Safari or assistive-technology certification.

See coordinates and output, reference data and lifecycle and saving for the integration contracts. Reproducible test fixtures and reference-generation scripts live in the source repository; local development reports are not shipped in npm packages or included in this website.