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> but the issue of things not lining up is primarily one of using coordinate systems correctly, knowing what things were measure in and what they are shown in
by plonk 4y ago
> but the issue of things not lining up is primarily one of using coordinate systems correctly, knowing what things were measure in and what they are shown in
Not in my experience. Two satellite/plane pictures from the same provider can be shifted by several meters. Buildings hand-drawn in OSM are rarely perfectly correct, and won't fit most images anyway due to the first point.
Conversions between coordinate systems are precise up to floating-point errors, that's the easy part and more or less solved by geo-referenced data formats.
- secretsatan 4y agoYes, but i’m finding, increasingly, that while we have the means to accurately record data, even accounting for float point errors by reducing area of coverage, things are simply not reported or cared about. It took us a considerable amount of investigation in using an rtk system to actually set things up correctly to get it to actually work within it’s 1cm accuracy. This is stuff like contacting rtk service providers to find out what system they actually correct their coordinates to. To me, the greatest innovation any provider could do is just specifying the coordinate system used EDIT: in fact i am finding it shocking, it’s even invoking government regulation, the simple fact is, even using advanced systems from leading suppliers, vital facts are just not recorded because geographic coordinates system are so numerous and complex suppliers just offer defaults and do the real work in the background Even here, i hope you don’t misunderstand a geographic system as we talk about all coordination systems, as opposed to geographic vs projected coordinate systems
- plonk 4y agoWhat data sources do you work with? I didn't know about RTK, it looks interesting but seems hardly applicable to satellite imagery, since it seems that you'd need a lot of receiving stations on the ground? My understanding is that providers like Maxar report coordinate systems correctly, but that errors in ortho-rectification (due to imprecise or wrong terrain altitude data) make it hard to make two images of the same area match exactly. > even using advanced systems from leading suppliers, vital facts are just not recorded because geographic coordinates system are so numerous and complex suppliers just offer defaults and do the real work in the background Not sure I understand what you mean by this. Do you get data that reports a coordinate system different from the one it actually uses?
- petrev01 4y agoIMO- an intro level college courses in GIS and/projections would go a long way here. I’ve often found that to be the case for the software community.
- plonk 4y agoI mean, maybe it would help, but I've already learned the basics of how projections and coordinate systems work, and I can't make the link with GP's "vital facts are just not recorded because [...] suppliers just offer defaults and do the real work in the background." Any online resources you'd recommend?