Projection - NAD27 to Nad83 Zone 13N

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10-19-2012 09:10 AM
NolaStein
New Contributor II
Hello,

I have lots of shapefiles in NAD 1927 Zone 13N which I would like projected to NAD 1983 Zone 13N. I have been trying to change the projection of these shapefiles but find the newly projected shapefile (NAD 83) is in the same exact spot as the previous shapefile (NAD27). I do not understand why the points have not shifted. I feel like this is a simple matter but I am having no success at finding the answer. I should also mention I am using ArcMap 10.1.

In terms of my method of changing the projection, it is as follows: Start a new map. Change the Data Frame Properties coordinate system to NAD 1983 Zone 13N. Add the NAD27 shapefile. Right click on the shapefile and export the data in the data frames coordinate system. Add the new shapefile to the map. After I complete this I find that the two shapefiles (NAD27 and NAD83) are showing the points to be in the same spot even though the properties tab shows the projections to be different.

Do I need to apply a transformation? I have been trying to figure out how to apply the CNT transformation but am not sure how to enter its information (see below). How do I use a CNT transformation? Should I even be using this transformation?

INPUT
PROJECTION UTM
UNITS METERS
DATUM NAD27 CNT
ZONE 15
PARAMETERS
OUTPUT
PROJECTION UTM
UNITS METERS
DATUM NAD83 CNT
ZONE 15
PARAMETERS
END

Thank you in advance for your help.

Sincerely,
Sarina
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MelitaKennedy
Esri Notable Contributor
Hi Sarina,

Yes, you need to apply a transformation. This is complicated by the fact that you probably do not have the file installed for the 'best' transformation for Canada.

First you'll need to download the grid file, Ntv2_0.gsb, from NRCanada.

Once you have it, browse to your ArcGIS installation folder and look for pedata. In pedata, go to ntv2. If there's a canada folder, copy Ntv2_0.gsb there. If there isn't, create a folder called canada and then copy the file there.

At this point, you'll need to restart ArcGIS if you haven't closed it already. Now when you change the data frame's coordinate system, click the Transformations button, and choose NAD_1927_To_NAD_1983_NTv2_Canada. Or use the Project Tool.

In 10.1, if the grid file isn't there, the transformation won't even be listed. That's a change from 10.0 and earlier, where the transformation would be listed, but wouldn't actually do anything because the underlaying grid wasn't there.

Melita

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NolaStein
New Contributor II
Does it show now difference in the points because it projects on the fly? If I look at the NAD 27 points in a new data frame and compare that to my NAD 83 data frame I can see a difference in the location of each point.

-Sarina
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MelitaKennedy
Esri Notable Contributor
Hi Sarina,

Yes, you need to apply a transformation. This is complicated by the fact that you probably do not have the file installed for the 'best' transformation for Canada.

First you'll need to download the grid file, Ntv2_0.gsb, from NRCanada.

Once you have it, browse to your ArcGIS installation folder and look for pedata. In pedata, go to ntv2. If there's a canada folder, copy Ntv2_0.gsb there. If there isn't, create a folder called canada and then copy the file there.

At this point, you'll need to restart ArcGIS if you haven't closed it already. Now when you change the data frame's coordinate system, click the Transformations button, and choose NAD_1927_To_NAD_1983_NTv2_Canada. Or use the Project Tool.

In 10.1, if the grid file isn't there, the transformation won't even be listed. That's a change from 10.0 and earlier, where the transformation would be listed, but wouldn't actually do anything because the underlaying grid wasn't there.

Melita
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