[GRASSLIST:5708] Re: v.proj problems - state plane to UTM

[Paul Kelly]

Hello there

On Sun, 2 Mar 2003, Philipp Molzer wrote:

> Hi,
> I'm using grass5.0.0 on Linux RedHat8 (intel).
> I have a DEM upon which I'd like to overlay some census data (vectors).
>  The DEM is in UTM format while the vectors are in state plane format.
>  Both locations are NAD83.  Both cover the area of Essex County, New
> Jersey, USA. When I use v.proj to bring the vectors from my state plane
> location to my UTM location, the resulting vector data has coordinates
> that seem to be incompatible with the DEM coordinates.  The east and
> west bounds of the imported vector layer appear to be way off.
>
> Also, I can't figure out how to change locations  except by exiting and
> restarting grass.

This is the conventional way to change locations. There is a new quicker
way but I can't remember it either. Exiting and restarting cleans up
temporary files etc. so it is a good idea to do it regularly.

> Source of vectors
>
> Vectors were imported into a location with these specifications:
>
>     name:    State Plane
>     datum:   nad83
>     dx:      0.000000
>     dy:      0.000000
>     dz:      0.000000
>     proj:    tmerc
>     a:       0.63782064e+07
>     es:      0.6768657997291094e-02
>     x_0:     0.6096012192024384e+06
>     y_0:     0
>     k:       0.999975e+00
>     lon_0:   74d40'w
>     lat_0:   38d50'n
>     -----------------------------------------------------------
>     PROJ_UNITS file:
>     unit:    foot
>     units:   feet
>     meters:  0.3048000000
>

I believe these are the wrong projection parameters. Some of them are for
state plane 1927 instead of 1983. This seems to be a bug in GRASS which I
have seen mentioned before. It is in src/general/g.setproj/get_stp.c . As
I am working on some minor improvements to g.setproj at the minute, I will
fix it, although it won't be for a few days.

For now I think the correct parameters in the PROJ_INFO file should be

name: State_Plane_1983_New_Jersey
datum: nad83
ellps: grs80
y_0: 0
es: 0.0066943800229
a: 6378137
dx: 0
dy: 0
dz: 0
lat_0: 38.8333333333333
f: 298.257222101
proj: tmerc
lon_0: -74.5
k: 0.9999
x_0: 150000

(got these from Eric Miller's website at
http://pweb.jps.net/~egm2/grass/STP/ )
You may also need to look into if the 'meters' value in the PROJ_UNITS
file is correct or should be 0.30480060960121920243 metres per foot
instead of 0.3048. Apparently this varies from state to state for state
plane 83.

I don't have any test points to check this so please let me know if it
works and I will try and fix the bug in GRASS.

Paul Kelly