[GRASSLIST:7957] Fwd: Re: nad27/nad83 datum conversion for canada using Ntv2

Feng Tan feng at lynxseismicdata.com
Wed Aug 17 16:20:47 EDT 2005

----------  Forwarded Message  ----------

Subject: Re: [GRASSLIST:7944] nad27/nad83 datum conversion for canada using 
Date: Wednesday 17 August 2005 13:46
From: Feng Tan <feng at lynxseismicdata.com>
To: Feng Tan <feng at lynxseismicdata.com>

Hi, Listers,

I just did some testing about nad27/nad83 datum conversion for a point in
Alberta, Canada using GRASS6.0 comparing with ESRI ARCGIS9.1, following is
the result, it has about +-100m difference with or without NTV2_0.GSB. I wish
GRASS can implement newer version of Canadian National Transformation
NTV2_0.GSB nad27/nad83 datum shift grid file soon, so we can use GRASS more
confidently. Right now GRASS6.0 still apply old ntv1_can.dat datum shift
file. I think this is very important issue and worth to put some effort in.

Here is the test:

I took 1 point in UTM coordinate system, nad27 datum and converted it to UTM
nad83 from GRASS6.0 and ESRI ArcGIS9.1

UTM_nad27: easting 889298.45 northing 8682992.65

1.) ArcGIS9.1 using NTv2_0.GSB datum shift grid file
UTM_nad83: easting 889220.78 northing 8683069.16

2)  GRASS6.0 cs2cs function using ntv1_can.dat datum shift file
UTM_nad83: easting 889200.13 northing 8683206.65

3) GRASS6.0 cs2cs function without applying ntv1_can datum shift file
UTM_nad83: easting 889277.91 northing 8683130.97

Please help!!



On Wednesday 17 August 2005 08:49, you wrote:
> Hi, List,
> 1.) I want to do datum conversion for Canada using Ntv2 grid file, how
> should I set up the locations for them? It seems grass6.0 only use
> Ntv1.data grid to set nad27 datum for canada (no option to use Ntv1.dat for
> nad83 datum), but Ntv2 version is more accurate grid shife file, how can I
> apply Ntv2 grid file for both nad27 and nad83 locations?
> 2.) If I use cs2cs to do the conversion for canada, what is the procedure
> for applying Canadian NTv2.gsb grid file?
> 3.) Did anybody evaluate the converted coordinate accuracy between last 2
> methods in GRASS6.0, or against other softwares such as ESRI and FME? What
> the outcome? Do they get the same results?
> Thanks,
> Feng


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