Georeferencing Aerial Photographs and pixel orientation

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04-24-2012 07:33 AM
GeospatialTechnology
Occasional Contributor
Hello,

I've been georeferencing some aerial photographs.

However they are all facing different directions so when I display them on top of each other all the pixels from each AP has a different orientation.

Is there any way of processing the raster images so all the pixels are the same orientation.

I'm not sure if this will mess up the image though?

Thanks for any help
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SteveKloiber
New Contributor II
When you use the georeferencing tool you should end up applying a transformation model to the image. When this happens, the pixels of the image are realigned to according to the model and to do this the pixel values will have to be resampled (e.g. nearest neighbor, bi-linear interp, or cubic convolution). I suspect that the precise orientation and alignment of the pixels will also be affected by your environment setting. Try setting your output coordinates. You could create an extent rectangle for your entire project area and then converting it to a simple grid and using that grid as your Snap Raster in the Output Coordinate section of your Environment Settings.
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JeffreySwain
Regular Contributor
If you are georeferencing them to the same coordinate system and choosing the option to 'Rectify' instead of 'Updating the Georeferencing,' then you should have created new rasters that have been resampled and should be 'oriented' the same way.  It sounds as if you may have updated the georeferencing or perhaps have them all georeferenced in the same MXD.  I would be sure they are rectified into the same coordinate system and then you should not have mis aligned pixels.
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GeospatialTechnology
Occasional Contributor
Thanks guys that does the trick!

The only thing I'm finding now though is that the rectified raster now has a big black square around it. Is there anyway of removing this or making it transparent?
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PrasantaBhattarai
Occasional Contributor II
Thanks guys that does the trick!

The only thing I'm finding now though is that the rectified raster now has a big black square around it. Is there anyway of removing this or making it transparent?

You can make it transparent by displaying the pixel value of 0,0,0 as NoColor
- Open properties for the image
- Go to symbology tab
- check on the display background value 0,0,0 as NoColor.
This will however make any valid 0,0,0 pixels from the image as no color.
If you need remove the black area permanently from the raster dataset, you might have to clip the black portion out using Clip (Data Management) tool.
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JeffBaker
New Contributor
I have the same problem with black or green areas and rectified rasters.  It seems to occur more when I have to rotate the raster being georeferenced.  Yes, I can reset the band values to zero to make them transparent, but I'd like to permanently set them to  nodata so I don't have to adjust the image each time I bring the raster into a map.  Suggestions?
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SantiagoTrujillo
New Contributor
I have the same problem with black or green areas and rectified rasters.  It seems to occur more when I have to rotate the raster being georeferenced.  Yes, I can reset the band values to zero to make them transparent, but I'd like to permanently set them to  nodata so I don't have to adjust the image each time I bring the raster into a map.  Suggestions?


Hi,

Try using the Setnull function that can be found in Map algebra, I havn't used this one myself but it seems to be crated for that purpose. You can also try using this document as a guide http://ibis.colostate.edu/WebContent/WS/ColoradoView/TutorialsDownloads/CO_RS_Tutorial2.pdf for another type of process.

Hope it works for you.
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