Issues using control points to georeference multiple rasters

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08-04-2015 06:34 AM
ChristinaHerrick1
New Contributor

I have successfully georeferenced a UAV-generated image (4-band) using the georeferencing toolbar (using the Update Georeferencing option to create a world file).  I saved my link table.  A colleague had generated a classification from the original (ungeoreferenced) image.  It has the same number of rows and columns, but pixel values are different and it has only one band (not four).  I want to georectify this image in the exact same way using the same control points and the exact projected coordinate system.  However, when I try to apply the control points to this new derivative layer, I get collinearity issues and the two images do not line up at all. 

I would think that they're practically the exact same image-- why wouldn't control points from the first image work to register the second image?  I did notice that when the images were brought into ArcGIS in their unregistered state, their extents do not match (see attached screenshot).  Any idea of a work-around for this?  Or do I manually have to georectify the second image?

Thanks

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XanderBakker
Esri Esteemed Contributor

I did a test and copied the .tfwx file, changed the name of the file to the second TIFF and that indeed did not have any effect on loading the second TIFF (still loads with the default coordinates). So, I did it using the alternative way, saving the tiepoints to a file, and loading that file for the second TIFF. Next did an Update Display followed by Update Georeferencing which did the trick. That would be an alternative.

However, I tried with another copy of the TIFF file. if you change the extension to of the worlfile to .tfw (yes loose the "x" in the extension) and load the TIFF, it actually loads correctly. For some reason the .tfwx file is not applied correctly.

Can you try again using the .tfw extension?

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6 Replies
BenGrod
Regular Contributor

Morning Christina,

I think you answered your own question when you mentioned the original extents of the two rasters do not match. When you bring an unreferenced image into ArcMap it displays where ever you place it, unless you can get the two images to align to the same original location then you can't use the same link table. The link table has several from (x,y) and to (x,y) which will only apply correctly if the original from location is exactly the same for both rasters. I think aligning the rasters originally might take as much time as manually georeferencing the second raster. Though someone in the community may have another solution. Hope this is helpful and good luck!

Ben

XanderBakker
Esri Esteemed Contributor

Since you have TIFF images, you can create the Word file (.tfw) from the georeferenced image, copy it and rename the copy of the .tfw the same name (leave the extension) as the second image. Make sure the image is not added to the session of ArcMap since the world file is read when you add the image to ArcMap.

See: World files for raster datasets—Help | ArcGIS for Desktop and Export Raster World File—Help | ArcGIS for Desktop

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ChristinaHerrick1
New Contributor

Hi Xander Bakker

I tried that.  No dice 😞  Still loads in the same spot off in no-where-land in the data frame with no spatial reference.  They're both tiffs, and so the world file has a *.tfwx extension.  This is what's in the world file.

 

0.045677623
-0.000313868
-0.000576502
-0.044168095
1821.654417
-2401823.433

At this point I just manually georeferenced the new raster, but I would still like to know if there is a work-around to this.

Thanks for your input@

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XanderBakker
Esri Esteemed Contributor

I did a test and copied the .tfwx file, changed the name of the file to the second TIFF and that indeed did not have any effect on loading the second TIFF (still loads with the default coordinates). So, I did it using the alternative way, saving the tiepoints to a file, and loading that file for the second TIFF. Next did an Update Display followed by Update Georeferencing which did the trick. That would be an alternative.

However, I tried with another copy of the TIFF file. if you change the extension to of the worlfile to .tfw (yes loose the "x" in the extension) and load the TIFF, it actually loads correctly. For some reason the .tfwx file is not applied correctly.

Can you try again using the .tfw extension?

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ChristinaHerrick1
New Contributor

Bingo!  Removing the 'x' from the world file extension did the trick.  Wonderful!  I did have to define the projection but the extent was finally updated.  Thanks so much for your help!

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ChrisDonohue__GISP
MVP Frequent Contributor

Just an idea - while both images have the same number of rows and columns, the two images cell-size are wildly different, so I suspect a scaling factor would need to be applied somehow.  Not sure on the specifics of how to implement that, however...

Chris Donohue, GISP

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