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Interesting that this is built on geojson which always uses WGS84 (the GPS coordinate reference system) as its CRS. WGS84 is pretty correct for almost everywher
by Mvandenbergh 6y ago
Interesting that this is built on geojson which always uses WGS84 (the GPS coordinate reference system) as its CRS. WGS84 is pretty correct for almost everywhere but is not typically used for local applications like this because physical locations drift relative to it and the WGS84 geoid (shape of the earth) won't give you a guaranteed locally flat surface that actually matches the elevation of the surface. It looks like they are just using ordinal levels relative to the the ground floor (defined as the lowest floor with level access to the outside) which is sensible but I wonder how they will use GPS signal to identify which floor a mobile user is on since GPS has poor vertical resolution and its not clear how much elevation data will be encoded in this format.
- toomuchtodo 6y agoI'd assume some sort of fusion between RF triangulation (mobile network and wifi) and barometric sensor would get a proper floor fix.
- Mvandenbergh 6y agoYou'd need to record the elevation of the floors as well relative to your RF reference frame though, otherwise you will know the phone elevation but not what floor it corresponds to. I would guess pico-cells assigned to particular floors in larger buildings.
- toomuchtodo 6y agoI’d expect this to occur (recording the elevation data) during surveying to build out the dataset. To your point about pico cells, I could see 5G high station density being beneficial. Very excited to see how data from new Apple mobile device LIDAR sensors are going to play into indoor mapping (hoping it nukes the premium Matterport charges).
- lincolnq 6y agoI don’t think they are relying GPS for any indoor stuff. They are using WiFi triangulation, including a WiFi survey you can upload where you walk around with an app and say where you are on the map. WiFi triangulation should be able to pick out your floor pretty accurately.
- twelvechairs 6y agoYes it would make a lot of sense to allow various local coordinate reference systems. Large internal plans could look distorted in wgs84 and in some parts of the world more than others!
- KaiserPro 6y agoIts so that they can anchor these maps to the world so that when they manage to bring in global vision location services (ie lyft, google walking maps, Scape's VPS) they can use any data that exists already and combine it with everything else.
- ben_w 6y ago> It looks like they are just using ordinal levels relative to the the ground floor (defined as the lowest floor with level access to the outside) which is sensible Sensible, but reminds me of my university. You walked uphill one floor from the base of the building to reach the main entrance, up a flight of stairs, along a short corridor, up four flights of stairs, along a long corridor, up another flight of stairs, and came out at ground level.
- WorldMaker 6y agoWhile RFC 7946 dropped support in GeoJSON for arbitrary CRS designation, the original 2008 standard supported it. It's a lovely interoperability problem that sometimes some applications will still produce GeoJSON in a CRS that isn't WGS84 and you get to shuffle it between tools until you get RFC 7946 compliant GeoJSON. There's obviously a small irony that in dropping CRS support to improve interoperability they added interoperability issues between "versions" of GeoJSON and what year an implementation was built and whether or not it support GeoJSON 2008 CRSes (and how it supports them because GeoJSON 2008 "kindly" let you specify the CRS at the FeatureCollection level, the Feature level, and the Geometry level and who knows what it meant when all three disagreed for the same Feature, so RFC 7946 was right to drop it because it was definitely a mess).