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When I use the NAD27 BLM 15N prj from the projected>>UTM>>north america>> in ArcMap 10.0 and go from WGS84 to that..using the NAD_27_To_WGS_84_1 transformation..my resulting shapefile doesn't line up with the wgs84 data.

I've set my data frame to each and tried new mxd's with no success of having them line up. Should they line up in ArcMap with re-projecting on the fly by ArcMap?

Thanks.

Justin
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  • Information about how the data do not "line" up can be useful for diagnosing the problem. Is there an approximately constant shift? If so, by how much in what direction? If not, what exactly are the relationships between the correct and misplaced features? – whuber Dec 27 '11 at 21:12
  • All the data points are shifted south/east to the original wgs84 lat/longs. If I project the data back to wgs84 those resulting points line up to the original wgs84. I do remember vaguely that NAD27 data will not line up with NAD83/WGS84. I also projected the orginil wgs84 data to nad83 and they line up. – Justin Dec 27 '11 at 21:31
  • How much are they shifted? – whuber Dec 27 '11 at 22:05

2 Answers2

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Are you setting the transformation in ArcMap as well? ArcMap (data frame) doesn't do it automatically. You may not be using the correct transformation either. #1 is for the Caribbean, but nothing farther north or west than Cuba. #4 is more general but possibly not as good as #79 (listed below)

Some other possibilities are:

15851: NAD_1927_To_WGS_1984_79_CONUS - lower 48 states (uses NADCON)

/* All below replaced by 15851 */ 15853: NAD_1927_To_WGS_1984_81 - offshore GoM between approx 95 W and 87 15 W (protraction areas) 15854: NAD_1927_To_WGS_1984_82 - offshore GoM west of approx 95 W (protraction areas) 15856: NAD_1927_To_WGS_1984_84 - offshore GoM outer continental shelf (protraction areas)

mkennedy
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  • In the project tool..it is forcing me to set a transformation and I tried a few (I think including #79). So if I am wanting to convert my WGS84 data to a UTM the resulting utm data should fall very close to the WGS84 data when brought into ArcMap with only the WGS original data with the Dataframe set to WGS84 by brining in the original data into a new mxd? Thanks. – Justin Dec 28 '11 at 00:47
  • If your data frame is in WGS84, you need to specify a transformation in the data frame properties in order for the UTM data to be projected on the fly correctly. – blah238 Dec 28 '11 at 01:51
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to just answer your question. yes
To expand on that...
if you have problems like this i would suggest starting with the original data and verify it's crs or gcs. *see below
the transformation you are using does not look correct to me.
In fact I rarely use a transformation when re-projecting from wgs to nad. If there is a problem with that I hope someone can correct it.

You should note that your transformation is backward from what you are trying to accomplish.

  1. add original data (only) to a new mxd.
  2. add other data that you have no question about crs.
  3. if they overlay then the original data is in the projection as stated in it's prj.
  4. if they don't overlay begin to examine first the coordinate values, then the scale to help determine the correct projection.
  5. search gis.stackexchange for answered questions (oops that should have been #1.
Community
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Brad Nesom
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