Posts by TerraLab

10 m vs 30 m, 5-day vs 8-day revisit, 13 vs 11 bands. Over one year near Rennes, Sentinel-2 gave 53 clear days and Landsat 30, with waits up to 33 vs 79 days.

Can ChatGPT automate QGIS? I asked it for PyQGIS code on three real tasks and ran every script in QGIS. What worked, what failed without an error, and why.

A CRS tells software where coordinates sit on Earth. Datums, EPSG codes, 4326 vs 3857, and a step-by-step fix for a layer that lands in the wrong place.

NDVI = (NIR - Red) / (NIR + Red), from -1 to 1. What each value range means, a season measured field by field, and the offset that turns 0.82 into 0.56.

Where to run PyQGIS, a first script, and a test on six tasks: chatbot code always ran, but one result was silently wrong when given only layer names.

QGIS is free, open-source GIS for Windows, macOS and Linux. What people use it for, what QGIS 4 changed in 2026, and the 10 most downloaded of 3,600 plugins.

Stream Sentinel-2 over STAC with no account, or get the L2A product from Copernicus Browser. Four methods tested on farms in Brazil, with timings.

QuickOSM fetched 4,560 buildings in 5 seconds; a whole country timed out. When to use QuickOSM, a Geofabrik .pbf (Kenya in 57 s), Overpass Turbo or an AI agent.

Layer > Georeferencer, 8 points, Polynomial 1 and a 34 s warp on a 1947 scan. Which transformation to pick, and why an RMSE of zero hid a map 594 m off.

The classified LiDAR HD cloud covered 78.4% of France on 6 September 2026, 30,933 of 34,877 communes. Map per commune, products, clicks in QGIS.