Projection Problems

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05-21-2012 09:03 AM
JeffGray1
New Contributor
I am in the process of changing the projections of all the data in my database.

First I am trying individual shapefiles to make sure they look right before I do it by batch.

I was directed to put them all in WGS_1984 as the new standard for our data.

Problem.  I have one good set projected in WGS_1984 and when I use that as the Import for the others, they don't line up.

But, if I leave the others in their original projection; NAD_27, 83, or whichever, they usually line up with the first one.  What is going on?

Thanks,

Jeff
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4 Replies
LucasDanzinger
Esri Frequent Contributor
Hi Jeff,

Just a thought, but are you setting a geographic transformation? The project tool says this is optional, but it isn't optional if you are moving between datums (from WGS 1984 to NAD 1983). The "Select the correct geographic (datum) transformation when projecting between datums" KB Article will point you to which transformation you should use. The important things to know are which datum are you coming from, which are you going to, and where your data are located on the Earth.

Luke
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MelitaKennedy
Esri Notable Contributor
Luke makes a good point. In a further clarification, how far off are the problematic datasets? It sounds like you may be using the data's property page or the Define Projection tool to change the coordinate systems. Is that correct? If so, that updates the metadata, but doesn't change the actual coordinate values. If the original datasets are actually in a projected coordinate system like a UTM or State Plane zone, the datasets after changed to WGS84 will show up wildly offset versus the 'good' data.

If this is the case, use the Project Tool instead (and leave the original coordinate system as-is.).

Melita
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ZheenbekKulenbekov
New Contributor
Hello people, I found a problem regarding extent of 2 geotiff files in ArcMap10, during overlaying them, 
I could not make overlapping them. What is the issue here? I do not know may be because of incorrect projection
I made transformation of projection from WGS 84 (no datum) to WGS UTM zone 43N (datum: GCS WGS 1984).

Now I have the first and second file extents which look different like below.
i.e. the first file has this extent,
                      top: 42,962420662
                 bottom: 41,814701751
                      left: 76,0234295884
                     right: 79,26404769

and the second file has this extent,
                       top: 4757306,86873
                  bottom: 4637621,26178
                       left: 585066,888521
                      right: 846865,929771

but other stuff like spatial reference, linear unit, angular unit, false easting and northing, scale factor,
central meridian are the same.
How to find right solution? I mean how can I get the same extent for both raster files?
Your help would be very appreciated.
Regards,
Jim
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LucasDanzinger
Esri Frequent Contributor
Zheenbek, you are seeing the different extents because one is still in a geographic coordinate system (most likely WGS 1984) and one is in a projected coordinate system. A GCS will have 1-3 digits to the left of the decimal (as they are measured in degrees) and a projected will have more, like 5-7 (as they are measured in linear units like feet or meters). If they both say in the properties that they are WGS UTM zone 43 N, then the one with 2 digits is incorrect. Like Melita said, perhaps the Define Projection tool was used to assign the PCS to the file, but it actually wasn't reprojected into the PCS. This means it is still stuck in GCS with a label or wrapper that says it is PCS. Try defining it back to WGS 1984 and then using the Project tool to project to your desired UTM zone.
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