GeoTIFF Raster Reprojection Lab
Reproject a small north-up GeoTIFF grid between WGS 84 geographic (EPSG:4326) and Web Mercator (EPSG:3857). Each target-cell center is inverse-projected into the source grid, resampled, and saved as a GeoTIFF that can be read back.
Key features
- Read a real GeoTIFF CRS, grid extent, bands and NoData before planning the opposite CRS
- Inverse-map target pixel centers and apply nearest-neighbor or bilinear resampling
- Preserve up to four numeric bands and per-band NoData output values
- Report requested/actual resolution, extent, valid/NoData cells and numeric projection round-trip difference
- Write a real uncompressed Float64 GeoTIFF and re-read its metadata before download
- Explicitly reject unsupported rotation, arbitrary CRS, palette, alpha, multi-image files and over-limit grids
How to use
- Choose a GeoTIFF or load the three-band example; inspect its source CRS, bounds and NoData.
- Select the opposite EPSG code and nearest or bilinear interpolation.
- Optionally enter target X/Y cell resolution in target-CRS units; blanks preserve the source cell count.
- Run reprojection and inspect target grid, NoData count and numerical reverse-check.
- Download the .tif and check its CRS, extent and bands in GIS.
Use cases
- Adapt a small numeric GeoTIFF grid to a Web Mercator map
- Compare interpolation and NoData boundaries when returning to a geographic grid
- Examine resolution differences for teaching grids without transmitting source imagery
Frequently asked questions
How is this different from resizing an image?
It maps each target grid cell center through an inverse CRS transform before reading a source band value. Its geospatial bounds, cell resolution and GeoTIFF coordinate tags change together.
Which CRS and files are supported?
Only one-image, north-up PixelIsArea GeoTIFFs explicitly tagged EPSG:4326 or EPSG:3857, transformed to the opposite CRS. Rotation, palettes, alpha, complex GDAL metadata, other CRS and multiple images are rejected.
How is NoData treated in bilinear interpolation?
If any contributing neighbor has NoData, that output band becomes NoData. Nearest uses its selected source sample. The report counts a cell as NoData when every band is NoData.
Are every source tag and compression preserved?
No. A new uncompressed Float64 GeoTIFF preserves georeferencing, sample values, band count and NoData. Source compression, styling, generic TIFF/GDAL metadata and color profiles are not copied. The library writer API is beta.
Does the round-trip number prove real-world location accuracy?
No. It is floating-point reverse-projection difference at four corners only. Resampling/cell error, original measurement quality, datum realization or epoch, and ellipsoidal distortion are not assessed.
Can this handle large satellite images?
This browser lab caps files at 8 MiB, source and output grids at 120,000 cells, four bands and 1024 cells per side. Large imagery, arbitrary projection and compression preservation need a dedicated GIS raster tool.
Privacy
The selected GeoTIFF stays in this browser tab. File reading, reprojection and downloads are local; this tool does not upload the input to its server API.
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