Handling Georeferenced Images From Terraserver

>Handling Georeferenced Images from Terraserver

Microsoft's Terraserver is a wonderful resource for spatially referenced aerial photographs. The spatial referencing allows you to very quickly tile together mosaics of high-resolution images. If you get the georefeerencing information with the image, and do the right things with it, it will align very well with other georeferencd data with very little trouble. If you have no other data, you can use this imagery as a very good spatial framework for beginning a GIS. The secret behind this georeferencing technique lies in the World File that can be downloaded with each image. There are a couple of tricky steps that you should go through to make sure that your images register with other data:

In this mini-tutorial we make use of terms and techniques that are discussed in the on-line manual pages: Map Coordinate Systems Explained and the Handling Projections in ArcMap

Note that since this tutorial was written, you may find newer or better imagery through the USGS Seamless Browser.

Getting Georeferencing INformation from Terraserver

First-off, before downloading your image, you should click the 'Info' button at the top of the screen, and get the metadata for the image. This will tell you whan the photo was taken.
The world-file must have the same name as the image, but a suffix of .jgw this is tricky because the default behavior of MS Internet Explorer will try to save this file with a suffix, '.aspx' You can avoid this when downloading the world-file by setting the Save as Type pulldown to All Files and then specifiying the suffix correctly when downloading.
In order to check that the world file has the correct suffix, you should look at it in your Windows Explorer, but make sure you have set your folder view options to view suffixes for known file types. Find this setting under Windows Explorer's Tools-Folder Options menu.
To double-Check that your image and the world-file are associated properly, look at the properties of the image in ArcCatalog. The extent of the image should not have 0,0 at the upper left corner. UTM coordinates are big numbers. If your extent has 0,0, at the upper left, then your world file is not named or saved properly.
Now set the projecdtion properties of the image to be the correct UTM zone. YOu can find that zone identified by the blue numbers on this map.
YOur terraserver image should now line up with any other GIS data you have, no matter what prpojections you may choose to use for your maps!




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				>Handling Georeferenced Images from Terraserver Microsoft's Terraserver is a wonderful resource for spatially referenced aerial photographs. The spatial referencing allows you to very quickly tile together mosaics of high-resolution images. If you get the georefeerencing information with the image, and do the right things with it, it will align very well with other georeferencd data with very little trouble. If you have no other data, you can use this imagery as a very good spatial framework for beginning a GIS. The secret behind this georeferencing technique lies in the World File that can be downloaded with each image. There are a couple of tricky steps that you should go through to make sure that your images register with other data: In this mini-tutorial we make use of terms and techniques that are discussed in the on-line manual pages: Map Coordinate Systems Explained and the Handling Projections in ArcMap *Note that since this tutorial was written, you may find newer or better imagery through the USGS Seamless Browser.* Getting Georeferencing INformation from Terraserver First-off, before downloading your image, you should click the 'Info' button at the top of the screen, and get the metadata for the image. This will tell you whan the photo was taken. The world-file must have the same name as the image, but a suffix of .jgw this is tricky because the default behavior of MS Internet Explorer will try to save this file with a suffix, '.aspx' You can avoid this when downloading the world-file by setting the Save as Type pulldown to All Files and then specifiying the suffix correctly when downloading. In order to check that the world file has the correct suffix, you should look at it in your Windows Explorer, but make sure you have set your folder view options to view suffixes for known file types. Find this setting under Windows Explorer's Tools-Folder Options menu. To double-Check that your image and the world-file are associated properly, look at the properties of the image in ArcCatalog. The extent of the image should not have 0,0 at the upper left corner. UTM coordinates are big numbers. If your extent has 0,0, at the upper left, then your world file is not named or saved properly. Now set the projecdtion properties of the image to be the correct UTM zone. YOu can find that zone identified by the blue numbers on this map. YOur terraserver image should now line up with any other GIS data you have, no matter what prpojections you may choose to use for your maps!