[GRASSLIST:1629] Re: More projection problems...

[Morten Hulden]

Matt,

Found some info of DOQ at 
http://edcwww.cr.usgs.gov/glis/hyper/guide/usgs_doq 
Wow, I wish 1m data was available for Europe too.

Seems like STP is hardcoded to use NAD27 datum in GRASS. DOQ uses NAD83,
so grass should actually read the parameters from state83 and not from
state27, but neither g.setproj or m.proj gives the user a choice.

An existing STP location is easy to fix by changing the false easting x_0
to 0.2e+06 (for your area) in the PROJ_INFO file.

But m.proj will still read the parameters from etc/state27. The quick and
dirty fix here is to rename the state83 file.

After doing this m.proj gets both your test points with a few meters/feet
from the expected values. I'm quite sure now that the central parallel of
the aea location is at 24N, not at 27.45 or 27.75.

There still is a 'outside current region' problem with r.proj though. I
think the different units (feet-meters) for the two locations has
something to do with it. I am currently looking into it.

You are probably the first to test r.proj on a STP location since the
module was changed a few months ago. Thanks for taking it up on the
list. We got a few new items on the TODO list.

Morten



On Fri, 16 Mar 2001, mberglund wrote:

> Ok, I have new coordinates.
> 
> This is a point for the intersection of a road.
> 
> Albers = (559764.34,573816.37)
> 
> STP    = (542947.15,1755093.74)
> 
> These are as measured.
> 
> I performed another point conversion, and I am still thousands of feet off
> on the x and a couple hundred on the y.
> 
> Can I arbitrarily change the False easting, to get what I want?
> 
> There is another issue that concerns me. I have a bunch of these to do if
> I can do the first one. If I use i.rectify, I will have to choose points
> like this for every quad sheet, right?
> 
> That negates possibilty of programmatically doing conversions, which was
> my ultimate goal.
> 
> Back to the grind I go...
> 
> Thanks,
> Matt
>