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Reprojecting the existing data

May 07 2010 | 0 comments
Categories: Map Data

I am having DEM downloaded from ASTER GDEM. It is having default projection as GCS WGS84. I want to convert it into UTM (zone 44N) WGS84. After using the tool -Project from Data Management toolbox -projection and
transformations-features it is changing the projection but spatial extents of the area are not changing. I have tried for all the available options but couldn't succeed. Can you please give us the proper methodology for assigning projection and changing existing projection of the shape file in ArcGIS?

Also, what should be the values of false Easting and False Northing while assigning UTM projection?

We will be thankful if could get some help to come out of the problem.

Mapping Center Answer:

First, if you are projecting a DEM, you should be using the Project Raster tool in the Raster toolset of the instead of the Project tool in the Features toolset. Both of these are in the Projections and Transformations toolset.

When you use the Project Raster tool, and you set the Output Coordinate System to UTM zone 44N (WGS84) using the WGS 1984 UTM Zone 44N.prj projection file, then the spatial extents WILL change.  This will become obvious if you look at the data in either ArcMap or ArcCatalog. 

For example, if you open ArcMAP, add a data frame and add the original data in GCS WGS84 coordinate system, then add another data frame, add the projected data in the UTM 44N projected coordiante system, the extents will look different.  To double check this, right click one of the DEMs in the table of contents, click Properties, then click the Data Frame tab.  Note the coordinates that are shown in the grayed out area next to the Fixed extent option.  Now do the same for the other DEM.

In ArcCatalog, navigate to the location of one of the DEMs, click the Preview tab and look at the map. Then click the Spatial tab and look at the projected or local coordinates.  Now do the same for the other DEM.  They will be different.

What WON'T change is the area of the earth that is represented in each of the two DEMs -- they will both cover the same amount of ground area.  To change this, you would need to clip the raster, not project it.

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