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Frequently Asked Questions (FAQ)

Coordinate Reference Systems (CRS)

Does samgeo automatically convert my imagery to EPSG:4326?

No. samgeo does NOT automatically reproject or convert your GeoTIFF files to EPSG:4326. Your imagery stays in its native coordinate system throughout the entire segmentation process.

Key points: - When you load a GeoTIFF with set_image() or use generate_masks_tiled(), the image data is read directly without any CRS transformation - The output masks inherit the same CRS as your input imagery - The reproject() function in samgeo.common has EPSG:4326 as a default parameter, but it's only used when you explicitly call that function - it is NOT called automatically during segmentation

Why might you see distortion? 1. Your visualization tool is displaying the results in EPSG:4326 (like some web map libraries) 2. You're manually calling the reproject() function somewhere in your workflow 3. Your original imagery already has CRS-related issues

Recommendation: - Verify your input TIF has the correct CRS metadata using gdalinfo or rasterio (src.crs) - The output masks will preserve the same CRS as your input - If you need to reproject for visualization, do it as a separate step AFTER segmentation: 

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from samgeo import common
common.reproject("input_masks.tif", "output_epsg4326.tif", dst_crs="EPSG:4326")

How can I check the CRS of my GeoTIFF?

Using GDAL: 

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gdalinfo your_file.tif

Using Python with rasterio: 

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import rasterio
with rasterio.open("your_file.tif") as src:
    print(f"CRS: {src.crs}")

My imagery looks distorted during segmentation

The segmentation algorithm works on pixel values, not geographic coordinates, so CRS should not affect segmentation quality. If you're seeing distortion:

  1. Check if it's a visualization issue: The distortion might only appear when viewing results in a different CRS
  2. Verify your input data: Use gdalinfo to check if the CRS metadata is correct
  3. Try reprojecting to a more suitable CRS: Some projections preserve shape better than others for specific regions (e.g., UTM for local areas)