additional markdown update in 15_polygon_fill.ipynb

Author: joshuacortez

notebooks/15_polygon_fill.ipynb

@@ -997,7 +997,7 @@
    "source": [
     "The output is a polars datafarame containing all the pixels within all the AOI polygons. The `unique_id_col` parameter can be used to assign to each pixel its corresponding geometry name from the original AOI. This saves us effort from having to perform another spatial join to get the geometry names.\n",
     "\n",
-    "If the original AOI is based on a geographic coordinate system such as `epsg:4326` or `epsg:3857`, then there would normally need to be an additional step to translate it from pixel coordinates back to geographic coordinates. To represent a pixel in geographic coordinates, you would need translate both the lower left corner and upper right corner to represent a rectangular polygon. But in this case it's not necessary to do the translation since the original AOIs are already based on pixel coordinates. You can refer to the implementations of [FastSquareGridGenerator](https://geowrangler.thinkingmachin.es/grids.html#fastsquaregridgenerator) and [FastBingTileGridGenerator](https://geowrangler.thinkingmachin.es/grids.html#fastbingtilegridgenerator) for examples of this translation."
+    "If the original AOI is based on a geographic coordinate system such as `epsg:4326` or `epsg:3857`, then there would normally need to be an additional step to translate it from pixel coordinates back to geographic coordinates. To represent a pixel in geographic coordinates, you would need translate both the lower left corner and upper right corner to represent a rectangular polygon. But in this case it's not necessary to do the translation since the original AOIs are already based on pixel coordinates. You can refer to the `_xy_to_bbox` method in [FastSquareGridGenerator](https://geowrangler.thinkingmachin.es/grids.html#fastsquaregridgenerator) and [FastBingTileGridGenerator](https://geowrangler.thinkingmachin.es/grids.html#fastbingtilegridgenerator) for reference."
    ]
   },
   {