Datum Conversion With NTV2

[Anonymous]

Hello,

I am wondering if anyone knows of a way of
checking to see if the NTV2 datum conversion from
the Government of Canada is being applied when
converting files in Map2000i.

We seem to have a strange shift in some of our
data, and though the NTV2 file has been copied to
the correct place we would like a double check to
make sure it is the conversion being applied.

Any help would be appreciated.

Bryan Waller

[Anonymous]

The only way I can think of to verify your transformation is to do an
inquiry on a point with known Lat and Long. Lat and Long should be the same
regardless of your projection if you have a common datum. I'm not sure which
Datum Canada uses. I would look up the Geodetic Coordinates of a government
control monument in the datums that you want to work with, then create a
dummy file and insert the point using one of the Datums. Transform it and
check the LAT and LONGS to see if they correspond to the government
coordinates.

"Bryan Waller" wrote in message
news:3D8A118E.348219AD@bdw.ca...
> Hello,
>
> I am wondering if anyone knows of a way of
> checking to see if the NTV2 datum conversion from
> the Government of Canada is being applied when
> converting files in Map2000i.
>
> We seem to have a strange shift in some of our
> data, and though the NTV2 file has been copied to
> the correct place we would like a double check to
> make sure it is the conversion being applied.
>
> Any help would be appreciated.
>
> Bryan Waller
>

[Anonymous]

About the only way I can think of to double check is to use the manual
conversion program INITGRID.exe that comes with the download. Enter a latlong
or a utm and convert from 27 to 83 or vice-versa Then enter those points
into two drawings and set the projection and datum. Query one drawing into
the other and they will (should) coincide. Don't forget that the file must
be in the special diectory and named ntv2.gsb

I use the transformations all the time and haven't had any problems.