Update README.md

README.md

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 license: apache-2.0
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+NAIP-S2 is a super-resolution dataset for remote sensing consisting of paired NAIP and Sentinel-2 images in the continental US.
+
+Data is divided into tiles.
+Each tile spans 512x512 pixels at 1.25 m/pixel in a UTM projection.
+At each tile, the following data is available:
+
+- NAIP: an image from 2019-2021 at 1.25 m/pixel (512x512).
+- Sentinel-2: between 16 and 32 images captured within a few months of the NAIP image at 10 m/pixel (64x64).
+- Sentinel-1: 4 images captured in the same year as the NAIP image at 10 m/pixel (64x64).
+- Landsat: 4 images captured in the same year as the NAIP image at 10 m/pixel (64x64).
+- OpenStreetMap: a GeoJSON containing buildings, roads, and 30 other categories. It uses pixel coordinates relative to the 512x512 NAIP image.
+- WorldCover: the 2021 land cover image at 10 m/pixel (64x64).
+
+
+Structure
+---------
+
+Once extracted, the dataset contains the different data types in different folders.
+Each folder contains files named by a tile ID, which consists of the UTM projection, column, and row.
+The column and row are based on tiles that are 512x512 pixels with pixel coordinates at 1.25 m/pixel, e.g. `32612_960_-6049.png` spans (614400, -3871360) to (615040, -3870720) in projection units.
+
+Here is an example of NAIP data:
+
+```
+naip/
+    32612_960_-6049.png
+    32612_960_-6050.png
+    32612_960_-6051.png
+    ...
+```
+
+And an example of Sentinel-2 data:
+
+```
+sentinel2/
+    32612_960_-6049_16.tif
+    32612_960_-6049_32.tif
+    32612_960_-6049_8.tif
+    32612_960_-6050_16.tif
+    ...
+```
+
+Note that the Sentinel-2 images are GeoTIFFs so they contain georeference metadata.
+Furthermore, the 10 m/pixel (`_8.tif`), 20 m/pixel (`_16.tif`), and 60 m/pixel (`_32.tif`) bands are stored separately.