Jan AdriaenssensUsing GPS in the year 1565
There’s a wonderful web app (“Allmaps Here”) that shows your GPS location on old maps. I love it.
https://www.verbeeld.be/2024/11/17/using-gps-in-the-year-1565/
Martin Jambon 🌍🌎🌏@verbeeld here's my location. The authors of the map didn't specify a publication date but it's ok because it's "correct".
https://here.allmaps.org/?url=https%3A%2F%2Fannotations.allmaps.org%2Fmaps%2F6fe39b2f7d71ae12
https://here.allmaps.org/?url=https%3A%2F%2Fannotations.allmaps.org%2Fmaps%2F6fe39b2f7d71ae12
@mjambon You can always make the georeferencing of these "correct" maps even more correct, by using this editor: https://editor.allmaps.org/#/
(It's a rabbit hole… I'm spending way too much time there georeferencing and correcting old (local) maps…)
@verbeeld I'll give it a try when I'm at my desk. I'm curious about how it works:
- the wiki aspect: how are plain mistakes and vandalism undone?
- the precision and distortion aspects: what's the algorithm to map user-entered geographic coordinates to image coordinates using reference points?
- the wiki aspect: how are plain mistakes and vandalism undone?
- the precision and distortion aspects: what's the algorithm to map user-entered geographic coordinates to image coordinates using reference points?
@mjambon These things I don't know — I'm only a fan of the site, but I'm not maintaining it, sorry…
@verbeeld I'll investigate
tim_fan@mjambon I have a similar project at https://onamap.me/
For the lat/lon to pixels algorithm, I use a triangulation of the reference points to interpolate u,v pixel coords based on pixel coords of nearby reference points
https://turfjs.org/docs/api/tin
@tim_fan cool. I don't have any need for it but I'm curious about dealing with bad data in practice and in theory. I.e. if one point is inconsistent with the majority, there should be a way to detect it and flag it. In practice, I suppose it depends on the application (e.g. are coordinates entered by a human who can make typos?).
@mjambon yeah I'm sure for my maps I make mistakes. All I do for error checking is to perform the forwards warping onto satellite imagery in QGIS, then visually check for discrepancies between the two. With this I can catch gross errors. E.g. overlay:
https://www.facebook.com/photo/?fbid=315155968310211
Beyond that, perhaps you could, on a per point basis, leave the point out of the referencing process, then see where it gets mapped to. If it is mapped far away from its reference location, perhaps the reference is wrong.
@tim_fan I suppose we could compare the Delaunay triangulations in both coordinate spaces and flag neighborhoods that are not preserved by the mapping.