[GRASSLIST:1630] Re: More projection problems...

[Morten Hulden]

On Sat, 17 Mar 2001, Morten Hulden wrote:

> 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.

No, there's not. I had just left a test PROJ_UNIT file around. r.proj
works OK now when the STP location is set to use NAD83 datum. 

Your testpoints with external proj:

(echo "557754.98 576793.94"| proj +proj=aea +ellps=GRS80 
+lat_0=24.000000000 +lat_1=24.0000000000 +lat_2=31.5000000000 
+lon_0=-84.0000000000 +x_0=400000.0000000000 +y_0=0.0000000000 -f %.6f -I|
proj +proj=tmerc +a=0.6378137e+07 +es=0.66943800229e-02 +x_0=0.2e+06
+y_0=0 +k=0.9999411764705882e+00 +lon_0=82dw +lat_0=24d20\'n -m
1:0.304800609601219202430 -f %.6f)

point 1
aea->stp
557754.98 576793.94 -> 536510.800084 1764930.245639
stp->aea
536507 1764928 -> 557753.796134 576793.250071

point2 
aea->stp
559764.34 573816.37 -> 542954.380909 1755073.347065
stp->aea
echo 542947.15 1755093.74 -> 559762.059432   573822.547514


I used +ellps=GRS80 in the command above, but WGS80 results differs only
from the fifth decimal. Using foot/meter ratio 0.304800609601219202430
insted of 0.3048 makes about one meter difference.

I think I read that original DOQ should be in UTM, so there probably was a
conversion step UTM->Albers before you got your aea map. That conversion
could attribute for the small errors that remain.

Morten