search

jedwards1211 / metacave

One cave survey data format to rule them all
5 stars 3 forks source link

geographic coordinates #14

Open jedwards1211 opened 5 years ago

jedwards1211 commented 5 years ago

@vpicaver I don't remember if we debated fixed station locations much but I kind of regret thinking we should just require all coordinates to be WGS84 lat/lon. As far as I understand, local coordinate systems can have particular advantages, for instance one of my friends who works with GIS was telling me that a station on the surface of the earth can move significantly with respect to a fixed global coordinate reference system over time (due to continental drift), whereas a station somewhere in the US would drift a lot less with respect to the NAD83 datum (excluding California, which is on a different tectonic plate).

Supporting local coordinates and multiple data/ellipsoids definitely increases the difficulty of supporting this format in any given program, but supporting more than one lat/lon point already requires using some kind of geodetic conversions library, so of course any program using a half-decent library for that would already have the routines they need available to handle more local coordinate systems.

Plus, most local coordinates in a file would most likely be in a single local coordinate system or UTM zone, in which case a program doesn't need to do any conversion at all (as opposed to > 1 lat/lon points).

So I'm thinking we should allow north/east fields in fixed stations for local coordinates, and not require datum/ellipsoid to be only WGS84 and add an optional utmZone field to the fixed station group.

I definitely don't think we should allow custom Proj4 strings like Survex does, but I can't decide whether we should encourage people to use EPSG numbers or just common names like WGS84, GRS80, NAD83, etc.

Any thoughts on this?

vpicaver commented 5 years ago

Sorry for taking so long to respond to this. I just saw the notification. I would suggest using WGS84 since I think it'll be good enough for cave survey. How much can local coordinate system move? Will we loose cave locations in our lifetime.

I don't think you want to mix UTM and WGS84. They're completely different projections. UTM is universal transverse mercator projection. The nice thing about WGS84 is that GPS units use it.