Live and recent posts from across the Fediverse tagged #surveying, aggregated by home.social.
Ground control took absolute accuracy from metres down to centimetres. The price: a few hours of fieldwork to survey the targets, and fifteen to twenty-five minutes of tagging them in the office.
So the only question that matters is what the map is for. A canopy index does not need it. A lawyer does.
The rule of thumb: a map's error should be a tenth of the thing you want to measure.
For a five metre stockpile, fifty centimetres of error is fine. For a crack in a wall, fifty centimetres is a disaster. The error number tells you whether the map is fit for the job.
Seven surveyed targets. Four become ground control, and the software fits the map to them exactly. Three are held back as checkpoints, and the software never sees them.
Compare the finished map against those three and the gap is the honest error of the whole survey. Three is the minimum. Five is better.
For most mapping, canopy work and change detection, relative accuracy is enough.
But when a map will be read by a surveyor, a client or a lawyer, it needs ground control. Without it every pixel can sit two to five metres from where it really is, and the processing report cannot tell you which way.
Awesome video by Daniel Steiner about the origin of the famous Swiss topo maps. 🇨🇭🗺️
Also he’s very lucky that because of his excellent geography videos, this latest video was in collaboration with the Swiss government. (I definitely recommend subscribing to his channel.)
#maps #cartography #Mapstodon #surveying #gischat #DanielSteiner #Swisstopo #Switzerland #Swiss