[Proj] NAD_1983_To_WGS_1984_5

[Hermann Peifer]

Hi Roger,

I might be wrong as I haven't really understood the details of your 
problem, but it looks to me that you want to get to these benchmark 
coordinates as a result of step 2:

1703671.30566227 424014.398045834
1704020.20113366 421943.708664294

I am getting pretty close, when using +nadgrids=@null in step 2, see below.

BTW, you specify too many parameters in your sample code: +ellps=GRS80 
+datum=NAD83 
+towgs84=-0.991,1.9072,0.5129,0.025789908,0.0096501,0.0116599,0.0

datum=NAD83 is a shortcut for "ellps=GRS80 towgs84=0,0,0" so you 
actually have 2 specifications for ellps and towgs84. This is why you 
end up with:

#--- following specified but NOT used
# +ellps=GRS80 +towgs84=0,0,0


Hermann


cat locs.xy # input coordinates for step 1
-121.524764291826 37.6600366036405
-121.523480804667 37.6543604613483

# step 1: transform and project to epsg 2227
cs2cs -f "%16.9f" +proj=longlat +datum=WGS84 +to +proj=lcc 
+lat_1=38.43333333333333 +lat_2=37.06666666666667 +lat_0=36.5 
+lon_0=-120.5 +x_0=2000000.0 +y_0=500000.0 +ellps=GRS80 +units=us-ft 
+no_defs 
+towgs84=-0.991,1.9072,0.5129,0.025789908,0.0096501,0.0116599,0.0 
locs.xy | tee locs.step1
6265039.137827862	2064418.929329731      1.854230785
6265388.042578982	2062348.222394954      1.854689702

# step 2: transform to epsg 26743
cs2cs -f "%16.9f" +proj=lcc +lat_1=38.43333333333333 
+lat_2=37.06666666666667 +lat_0=36.5 +lon_0=-120.5 +x_0=2000000.0 
+y_0=500000.0 +ellps=GRS80 +units=us-ft +no_defs +nadgrids=@null +to 
+init=epsg:26743  locs.step1

1703671.305672543	424014.398046337      1.854230785
1704020.201144472	421943.708664825      1.854689702


On 2014-08-30 14:04, Roger Bivand wrote:
> Hi,
>
> I'm aware of Frank's reply:
>
> http://lists.maptools.org/pipermail/proj/2008-September/003833.html
>
> but would value clarification of why this happens (further details on:
>
> https://stat.ethz.ch/pipermail/r-sig-geo/2014-August/021611.html
>
> from WGS84 geographical coordinates to NAD27 via WGS84_5).
>
> (code attached to get around line breaks)
>
> The first test using cs2cs is wrong because it doesn't use +towgs84= to
> use *_5:
>
> (the test is against benchmark coordinates)
>
> The works in the first sub-step (geographical to WGS84_5 State Plane):
>
> So locs.step1 are OK, but the next step gets the same errors as ignoring
> *_5
>
> Turning on -v shows:
>
> cs2cs -v -f "%16.9f" +proj=lcc +lat_1=38.43333333333333
> +lat_2=37.06666666666667 +lat_0=36.5 +lon_0=-120.5 +x_0=2000000.0
> +y_0=500000.0 +ellps=GRS80 +datum=NAD83 +units=us-ft +no_defs
> +towgs84=-0.991,1.9072,0.5129,0.025789908,0.0096501,0.0116599,0.0 +to
> +init=epsg:26743 < locs.step1
>
> # ---- From Coordinate System ----
> #Lambert Conformal Conic
> #    Conic, Sph&Ell
> #    lat_1= and lat_2= or lat_0
> # +proj=lcc +lat_1=38.43333333333333 +lat_2=37.06666666666667 +lat_0=36.5
> # +lon_0=-120.5 +x_0=2000000.0 +y_0=500000.0 +ellps=GRS80 +datum=NAD83
> # +units=us-ft +no_defs
> # +towgs84=-0.991,1.9072,0.5129,0.025789908,0.0096501,0.0116599,0.0
> #--- following specified but NOT used
> # +ellps=GRS80 +towgs84=0,0,0
> # ---- To Coordinate System ----
> #Lambert Conformal Conic
> #    Conic, Sph&Ell
> #    lat_1= and lat_2= or lat_0
> # +init=epsg:26743 +proj=lcc +lat_1=38.43333333333333
> # +lat_2=37.06666666666667 +lat_0=36.5 +lon_0=-120.5 +x_0=609601.2192024384
> # +y_0=0 +datum=NAD27 +units=us-ft +no_defs +ellps=clrk66
> # +nadgrids=@conus, at alaska, at ntv2_0.gsb, at ntv1_can.dat
>
> Puzzled,
>
> Roger
>
>
> NAD83_WGS84_5_test.txt
>
>
> cat > locs.xy << EOF
> -121.524764291826 37.6600366036405
> -121.523480804667 37.6543604613483
> EOF
>
> cs2cs -f "%16.9f" +proj=longlat +datum=WGS84 +to +init=epsg:26743 locs.xy | awk '{if (NR == 1)
>   printf("%16.9f %16.9f\n", 1703671.30566227-$1, 424014.398045834-$2)
>   else
>   printf("%16.9f %16.9f\n", 1704020.20113366-$1, 421943.708664294-$2)
> }'
>
> cs2cs -f "%16.9f" +proj=longlat +datum=WGS84 +to +proj=lcc +lat_1=38.43333333333333 +lat_2=37.06666666666667 +lat_0=36.5 +lon_0=-120.5 +x_0=2000000.0 +y_0=500000.0 +ellps=GRS80 +datum=NAD83 +units=us-ft +no_defs +towgs84=-0.991,1.9072,0.5129,0.025789908,0.0096501,0.0116599,0.0 locs.xy > locs.step1
> awk '{
> if (NR == 1)
>   printf("%16.9f %16.9f\n", 6265039.1378244-$1, 2064418.92932968-$2)
>   else
>   printf("%16.9f %16.9f\n", 6265388.04257557-$1, 2062348.22239488-$2)
> }' locs.step1
>
> cs2cs -f "%16.9f" +proj=lcc +lat_1=38.43333333333333 +lat_2=37.06666666666667 +lat_0=36.5 +lon_0=-120.5 +x_0=2000000.0 +y_0=500000.0 +ellps=GRS80 +datum=NAD83 +units=us-ft +no_defs +towgs84=-0.991,1.9072,0.5129,0.025789908,0.0096501,0.0116599,0.0 +to +init=epsg:26743 < locs.step1 | awk '{
> if (NR == 1)
>   printf("%16.9f %16.9f\n", 1703671.30566227-$1, 424014.398045834-$2)
>   else
>   printf("%16.9f %16.9f\n", 1704020.20113366-$1, 421943.708664294-$2)
> }'
>
>
>
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