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I am trying to use proj4js to convert between WGS84 (4326) to NAD27 BLM 14N (ftUS) (32064). I am using this definition for EPSG 2674 

`proj=tmerc +lat_0=0 +lon_0=-99 +k=0.9996 +x_0=500000.001016002 +towgs84=-8,161,176 +y_0=0 +ellps=clrk66 +to_meter=0.3048006096012192 +no_defs "`

I have also tried:

proj=tmerc +lat_0=0 +lon_0=-99 +k=0.9996 +x_0=500000.001016002 +datum=NAD27 +y_0=0 +ellps=clrk66 +to_meter=0.3048006096012192 +no_defs "

I got the transformation Parameters from here and have gone through these three similar SO posts one, two, three. My proj4js transformation remains about 100ft off. I'm validating the result using both corpscon and blue marble. I can accept the limitations of a 7 parameter transformation but can't find suitable values for the Gulf of Mexico. 3 parameters are not tight enough. How do I form the proj definition to get this to work.

The coord pair I am using to test is 25.340631, -96.647033 the expected result for EPSG 26714 is 9201257.09usft,2417471.02usft.

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risail
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  • Can you provide sample coordinate pairs? – AndreJ Aug 10 '16 at 06:03
  • For the 2nd case, add +nadgrids ? (I'm not sure of the name) Do you have the NADCON grid files installed? On both, the x_0 value should just be 500000, even though that won't make a difference to your offset. – mkennedy Aug 10 '16 at 12:04
  • I would probably also use EPSG:1174 (eastern US) with -9,161,179 or look at EPSG:15852-54 which were developed for the GoM (if that's where the data is) – mkennedy Aug 10 '16 at 12:10
  • @AndreJ I edited my question and included coordinates, @mkennedy I was under the impression that proj4js does not support grid files. 3 parameters towgs84 is 1-sigma but 7 will get me close enough for what I am doing, I cant find 7 params for GOM though. You are correct I am in the GOM but 1174 & 15852 are geographic I'm trying to go From WGS84 to a NAD27 projection be it NAD27 UTM XXN or NAD27 BLM XXN. – risail Aug 10 '16 at 13:42

1 Answers1

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Using cs2cs (pure proj.4) with -96.647033 25.340631 in an input file named BLM.txt, I have run these calculations:

echo WGS84-32064 (us-ft) >out.txt
cs2cs +init=epsg:4326 +to +init=epsg:32064 <BLM.txt >>out.txt
echo WGS84-26714 (m) >>out.txt
cs2cs +init=epsg:4326 +to +init=epsg:26714 <BLM.txt >>out.txt
echo WGS84-towgs84 >>out.txt
cs2cs +init=epsg:4326 +to +proj=tmerc +lat_0=0 +lon_0=-99 +k=0.9996 +x_0=500000.001016002 +towgs84=-8,161,176,0,0,0,0 +y_0=0 +ellps=clrk66 +to_meter=0.3048006096012192 +no_defs <BLM.txt >>out.txt
echo NAD27-grid >>out.txt
cs2cs +init=epsg:4326 +to +proj=tmerc +lat_0=0 +lon_0=-99 +k=0.9996 +x_0=500000.001016002 +datum=NAD27 +y_0=0 +ellps=clrk66 +to_meter=0.3048006096012192 +no_defs <BLM.txt >>out.txt
echo WGS84-tfm15852 (87.25 to 0w)>>out.txt
cs2cs +init=epsg:4326 +to +proj=tmerc +lat_0=0 +lon_0=-99 +k=0.9996 +x_0=500000.001016002 +towgs84=-3,154,177 +y_0=0 +ellps=clrk66 +to_meter=0.3048006096012192 +no_defs <BLM.txt >>out.txt
echo WGS84-tfm15853 (95 to 87.25w) >>out.txt
cs2cs +init=epsg:4326 +to +proj=tmerc +lat_0=0 +lon_0=-99 +k=0.9996 +x_0=500000.001016002 +towgs84=-7,151,175 +y_0=0 +ellps=clrk66 +to_meter=0.3048006096012192 +no_defs <BLM.txt >>out.txt
echo WGS84-tfm15854 (west of 95w) >>out.txt
cs2cs +init=epsg:4326 +to +proj=tmerc +lat_0=0 +lon_0=-99 +k=0.9996 +x_0=500000.001016002 +towgs84=-7,151,178 +y_0=0 +ellps=clrk66 +to_meter=0.3048006096012192 +no_defs <BLM.txt >>out.txt

to get these results:

WGS84-32064 (us-ft) 
2417471.02  9201257.09 0.00
WGS84-26714 (m) 
736846.64   2804548.77 0.00
WGS84-towgs84 
2417490.04  9201247.36 139.20
NAD27-grid 
2417471.02  9201257.09 0.00
WGS84-tfm15852 (87.25 to 0w)
2417470.98  9201253.01 118.89
WGS84-tfm15853 (95 to 87.25w) 
2417482.69  9201263.98 111.49
WGS84-tfm15854 (west of 95w) 
2417482.85  9201255.09 107.28

Your point should lie in the last zone, and the result is about 12 feet from the grid file solution. Plotting the various points on a map with feet grid looks like this:

enter image description here

AndreJ
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