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I kept coming across stunning Sentinel-2 images of Tenerife on Twitter: Snow covering Teide all the way down to 2,000 meters, calima turning everything sepia, the green that shows up in spring after the rains, the wild surface currents off the north coast in September, the blatant scar of the 2021 eruption in La Palma. The Canaries are home for me and I wanted that view on my desktop, updating every day to reflect what the islands actually look like right now.
This project fetches recent Sentinel-2 L2A imagery from the Element 84 Earth Search STAC API, stitches random mosaics of 10km MGRS subtiles into a composite image, applies Copernicus-style true-color tone mapping, and sets it as my wallpaper. Every run picks a different cloud-free region of the archipelago, so the image rotates through different islands, coastlines, and seasons.
A few things make it more interesting than a simple image download. A precomputed candidate list defines which subtiles have enough land to be worth showing. The mosaic selector builds all valid contiguous grids from those candidates and samples from them at random, weighted toward subtiles that actually passed a 98% valid-pixel threshold for the chosen date. A tile status cache remembers which dates and subtiles came back cloudy or incomplete, so repeated runs don't re-fetch useless data.
Scheduling is handled by a cron job that runs three times a day. On macOS Sequoia, setting wallpaper programmatically requires some extra work to propagate across spaces, which the project handles by updating the wallpaper plist directly.
Source code on GitHub.
