[OSM-talk] Affordable 1 CM high precision GPS.

[Greg Troxel]

john whelan <jwhelan0112 at gmail.com> writes:

> It depends on the requirements.  I think mapping from Bing imagery is quite
> reasonable and that isn't done to 1 cm accuracy.

Sure.  mapping from 15 cm imagery that is actually georeferenced
properly is 100% fine but it does not work in tree cover.  Also actually
georeferenced properly is hard to evaluate.  MassGIS imagery and RTK
line up super well.

> However as you point out there are other solutions and I'm not advocating
> one specific solution merely that it exists.  If there is a requirement
> that needs high accuracy then this might work.

I didn't mean to criticize the video I didn't watch.

I just meant that 10 cm accuracy gets you really high value in mapping,
and I don't think going from 10 to 1 helps that much.

Also people need to be clear on what datum the reference network is in,
and at 1 cm they need to be clear on their local plate motion.  North
America is moving at about 3 cm/year and some other places are double
that.

> Perhaps it needs a wiki entry to list the advantages and disadvantages of
> different approaches.  Certainly locally imagery is much better than GPS
> near tall buildings.

non-rtk, yes.  But imagery is challenged if the height models are off,
because it is slant and reduced to be apparently vertical.


Unfortunately all of this is pretty hard.


> Another issue is if you have two things in the map one that has been mapped
> with high accuracy and one not there isn't really anyway to tell which is
> the high accuracy one.

True.  We need accuracy metadata on coordinates; I put "RTK GNSS" in my
changeset comments when that's how it is.