[Proj] So close -- Lat / Long to Pennsylvania State Plane North NAD27

[Melita Kennedy]

I tried the same conversions in the Esri projection engine (that is used in ArcMap). 

Given:
-75.921819 41.295735

If I use 15851 (NAD_1927_To_WGS_1984_79_CONUS), I get:

2502234.97257 416637.87163

If I omit the geographic/datum transformation, I get:

2502332.65811 416669.37540

Melita


-----Original Message-----
>Date: Fri, 26 Jul 2013 16:53:01 +0200
>From: Andre Joost <andre+joost at nurfuerspam.de>
>Subject: Re: [Proj] So close -- Lat / Long to Pennsylvania State Plane
>	North	NAD27
>To: proj at lists.maptools.org
>
>Am 26.07.2013 14:22, schrieb jdawg:
>> sorry...bumping this message to get it on the mailing list... :)
>>
>>
>
>Unfortunately, your first message did not get to the mailing list, only
>to nabble readers. For the record, I paste it below.
>
>I did some tests with the following commands on GDAL 1.10.0:
>@echo off
>
>echo WGS84-NAD27 >out.txt
>cs2cs +init=epsg:4326 +to +init=epsg:4267 WGS84.txt >>out.txt
>echo WGS84-NAD27PAft>>out.txt
>cs2cs +init=epsg:4326 +to +init=epsg:32028 WGS84.txt >>out.txt
>echo NAD27-NAD27PAft>>out.txt
>cs2cs +init=epsg:4267 +to +init=epsg:32028 WGS84.txt >>out.txt
>
>with the follwoing input file WGS84.txt:
>-75.921819 41.295735
>
>and got those results:
>
>WGS84-NAD27
>75d55'19.837"W	41d17'44.355"N 0.000
>WGS84-NAD27PAft
>2502234.97	416637.87 0.00
>NAD27-NAD27PAft
>2502332.66	416669.38 0.00
>
>So you get the first result if the input is regarded as WGS84 degrees, 
>and the second if the input is regarded as NAD27 degrees (EPSG:4267).
>
>HTH,
>Andr? Joost
>
>
>Original message:
>
>> This is my first time using Proj.4, and I'm struggling with
>> converting Lat/Lon in decimal degrees to Pennsylvania State Plane
>> North NAD27. I'm very unfamiliar with coordinate system terminology.
>> Here's what I'm expecting based on what our mapping system tells me
>> are the coordinates between the two systems:
>>
>> -75.921819, 41.295735
>>
>> should return
>>
>> 2502235.76228      416637.89162
>>
>> when I convert it using cs2cs. (I'm expecting these values because
>> when I use ArcMap to convert the coordinate system using the
>> transformation called "NAD_1927_To_WGS_1984_79_CONUS", I get those
>> values.) But what I'm getting from cs2cs is:
>>
>> 2502332.66      416669.38
>>
>> This is the command line syntax I'm using, along with the output:
>>
>> C:\proj\bin>cs2cs -v +proj=latlong +datum=NAD27 +ellps=clrk66
>> +nadgrids=conus,nt v1_can.dat +to +init=epsg:32028 # ---- From
>> Coordinate System ---- #Lat/long (Geodetic) # # +proj=latlong
>> +datum=NAD27 +ellps=clrk66 +nadgrids=conus,ntv1_can.dat #---
>> following specified but NOT used # +ellps=clrk66
>> +nadgrids=conus,ntv1_can.dat # ---- To Coordinate System ----
>> #Lambert Conformal Conic #       Conic, Sph&Ell #       lat_1= and
>> lat_2= or lat_0 # +init=epsg:32028 +proj=lcc +lat_1=40.88333333333333
>> +lat_2=41.95 # +lat_0=40.16666666666666 +lon_0=-77.75
>> +x_0=609601.2192024384 +y_0=0 # +ellps=clrk66 +datum=NAD27
>> +to_meter=0.3048006096012192 +no_defs # +nadgrids=conus,ntv1_can.dat
>> #--- following specified but NOT used # +ellps=clrk66 -75.921819
>> 41.295735 2502332.66      416669.38 0.000
>>
>>
>> The values are so close, but not close enough, and I can't figure out
>> where the discrepancy is! Can any of you gurus advise me in this
>> matter?? Thanks very much!!
>>
>> Jeremy
>
>End of Proj Digest, Vol 110, Issue 7
>************************************