Posts by TerraLab

An orthophoto is one aerial photograph corrected to a map. An orthomosaic is many of them stitched into one image. Which one you have, and where the seams are.

Semantic segmentation labels every pixel with a class: building or not. Instance segmentation draws every building as its own object. On a terraced street the difference is one polygon against forty.

Describe a task in plain language and it runs in your open QGIS project: load data, run algorithms, style layers, build a layout. Every run can be undone.

A greenfield site has never been built on. A brownfield site has, and may still carry what the last use left behind. How to tell them apart in QGIS.

Browser panel, XYZ Tiles, double-click OpenStreetMap. Then Google, Esri and Bing by URL, national imagery by WMS, and which basemap a detection model can read.

A DSM is the height of the top of everything: roofs, treetops, bare ground. A DTM is bare ground alone. Subtract one from the other to get what stands on it.

Flat, watercolor, pencil and glossy, all rendered from one aerial image of Letchworth Garden City. Every prompt in full, and where the model invented water.

Check OpenStreetMap first. Then four ways to map rooftop PV from aerial imagery in QGIS, with the menu paths and where each one fails.

Start with QuickOSM on leisure=swimming_pool. Where the map is thin, threshold the blue, run a water index, or use a segmentation model. Five methods compared.

Start with QuickOSM. Where OSM is thin, five more ways to get roads out of imagery, and the line-or-surface choice that decides all of them.