[PROJ] Problem converting to State Plane Coordinates

[Greg Troxel]

US State plane systems today are (almost always?  always?) projections
of NAD83.  Some states have multiple zones.  Typical projections are TM
and Lambert Conformal Conic (LCC), typically for NS and EW states or
chunks.  Note that while there are 6-degree-wide standard UTM zones
(that's the U in UTM, universal) state plane TM systems are not
necessarily UTM, and I think typically aren't.

4302 I think is a FIPS code, not an EPSG or ESRI code, and thus won't
show up in proj.  It looks like LCC.

A major wrinkle, probably in the past, is that there were state plane
systems that are projections of NAD27.

Another wrinkle is the varying realizations of NAD83, but I hope you are
in "NAD83(2011) epoch 2010.0".

The other wrinkle is that state plane systems are varyingly ins ft, ftUS, m.

It looks like central Utah zone is:
  http://epsg.io/2850

so you need to

  be clear on which state plan: NAD27 vs NAD83, ft vs m
  be clear on datum of source coordinates

and then

   find the epsg code for your source data (NAD83?)
   find the code for state plane, maybe EPSG:2850 code
   use cs2cs


Kristian is I think right that the state plane is only a projection, but
it's then true that to interpret coordinates in state plane you need an
associated datum.

If your source data is WGS84, that's messier.   You can:

  decide to be ok with the sort-of-true not-really-true notion that it's
  equal to NAD83, if you don't care about a meter or maybe 2.

  find out which WGS84 it really is, and if modern, label it ITRF2014,
  which will cause proj to transform it.  This is tricky business and
  you may want to ask your state geodetic advisor, if you really have
  this situation and really care about a meter, and don't already
  understand all of this
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