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Mismatching projections

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#1
pulecz

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I know projection mismatches are pretty common errors, but I'm stuck and don't know how to move on.

 

I've created a shapefile out of decimal coordinates stored in DBF and set it a national S-JTSK projection in ArcCatalog. I set the same projection in the Data Frame Properties in ArcGIS 9.3. Then, I load a polygon shapefile that has got the same projection and should overlap but those two just don't match. That red dot is in fact over 1800 separate locations.

 

Not just the location but even the scale is vastly different. Tried that even in Quantum GIS with the same result. I'm clearly missing
something basic here. Can anyone help me out with any tips, please?

 

 

mapa.jpg


Edited by pulecz, 26 May 2013 - 02:09 PM.

Martin

www.geographics.cz

#2
frax

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Could it be that those polygons are incorrect? Try to pull in some ArcGIS online data, or data from the ESRI Data & Maps cd/dvd, maybe? (or natural earth)


Hugo Ahlenius
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#3
souvik.gis

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Sir,

for which the coordinate have to fix? I have some experience regarding co-ordinate fixation. You can try this steps: ----

1. remove the coordinate information from the vector file.

2. Find two area where both file should marge.

3. Open the correct file first and than rectify the second one.

 

I will wait for your responce.



#4
mfarmer

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Just to state the obvious: something has the wrong projection/coordinate system. Have you worked with the polygon features before with other projected features, and have them line up correctly with other data? If that's the case, then rename the .prj of the points to .prj.bak; and start troubleshooting the correct projection for your points. I would guess that the points' coordinates are a bit more universal: decimal degree, WGS84, UTM, etc., but that's just a stupid guess.

 

The way I troubleshoot for unknown coordinates is first to start with a blank map document (remember that ArcMap sets the data frame's projection property to that of the first shapefile or feature class that's loaded into the data frame). Then load the shapefile with the renamed projection file, and look at the coodinates at the bottom of the map document window. The data frame will still have an unknown coordinate system. See if those coordinates look familiar (decimal degree, continental system, WGS84, UTM, etc.), I may get lucky. Then load a shapefile with a known good projection file that should overlay the points.

 

If that works, great. Define the projection with the one you know works, delete the .prj.bak file, and you're good to go. If that doesn't work, then you can try setting the data frame's p/cs property until you find one where the two shapefiles line up properly (ArcMap will automatically move the shapefile with the known good .prj to the correct location, based on the data frame's p/cs property). Then define the points' projection to the one you just found.

 

The problem with troubleshooting is that sometimes trouble shoots back.



#5
pulecz

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Thank you guys for your tips!

 

However, of course I was missing something awfully basic. The projection I was setting to the new shapefile (red) was correct, it is just defined by totally different coordinates than decimal degrees. So the problem was already in the csv file in the very definition of the coordinates. Transformed them into the right format and it works fine. Magnificent facepalm, still not sure how it couldn't have occured to me...

 

Appreciate your help, though! Let it reside here for others to use.


Martin

www.geographics.cz





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