Hi Guodong,

If you save the .gif and the .gfw file to the same directory, so that they are siblings, rasterio will find the .gfw automatically when the .gif file is opened. This behavior is inherited from the GDAL library that rasterio uses and is a common GIS paradigm. Many GIS file formats are actually multi-file formats. One file, usually the image file, is the primary file and it may have auxiliary or "sidecar" files that carry additional information. A world file is one such auxiliary file.

Because rasterio's programs don't handle colormapped images well, I suggest that you use the GDAL programs instead. Like this:

gdal_translate -of GTiff -a_srs EPSG:4326 latest_radaronly.gif latest_radaronly.tif

gdalwarp -r near -t_srs EPSG:3857 latest_radaronly.tif warped.tif

Rasterio's rio-info program will show you the bounds

$ rio info warped.tif
{"bounds": [-14207635.496435506, 2470074.029222458, -7406084.60511778, 6518566.074162895], "colorinterp": ["palette"], "count": 1, "crs": "EPSG:3857", "descriptions": [null], "driver": "GTiff", "dtype": "uint8", "height": 1922, "indexes": [1], "interleave": "band", "lnglat": [-97.07967556953324, 37.395081418108624], "mask_flags": [["nodata"]], "nodata": 0.0, "res": [2106.3954448181253, 2106.3954448181253], "shape": [1922, 3229], "tiled": false, "transform": [2106.3954448181253, 0.0, -14207635.496435506, 0.0, -2106.3954448181253, 6518566.074162895, 0.0, 0.0, 1.0], "units": [null], "width": 3229}

The rio-bounds program will give you the bounds as GeoJSON

$ rio bounds warped.tif
{"bbox": [-127.62936117647057, 21.654332979481737, -66.5299899625959, 50.41561201989618], "geometry": {"coordinates": [[[-127.62936117647057, 21.654332979481737], [-66.5299899625959, 21.654332979481737], [-66.5299899625959, 50.41561201989618], [-127.62936117647057, 50.41561201989618], [-127.62936117647057, 21.654332979481737]]], "type": "Polygon"}, "properties": {"filename": "warped.tif", "id": "0", "title": "warped.tif"}, "type": "Feature"}