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Is there a way to trim a geo-referenced air photo to an irregularly shaped boundary? I tried the clip tool shown in my attachment, but it didn't work. It looks as though the output extent field requires a rectangularly shaped polygon as the clipping feature. Can I even do this in ArcView? I've never had a request to do anything like this before.

enter image description here


I do use Photoshop and other similar software packages. I could just go in to an environment like this & start painting everything outside of my boundary in white, but then I would have to come back in and geo-reference the image again, and it just strikes me that there must be a faster and easier way (even though I only have ArcView 9.3).

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Did you try to set a Mask ( help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//… )? you could then use the raster calculator to produce a new raster from the input raster. –  Dan Patterson Apr 14 '11 at 19:25
    
@ Dan P. - No actually. I have used similar techniques in Corel Paint Shop Pro for different reasons (long time ago). I only have ArcView, and ONLY 9.3. Will my software do what you've proposed before I get too deep in to the reading? –  Dano Apr 14 '11 at 19:40
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I think the extract by polygon tool will work, but that was some time ago webhelp.esri.com/arcgisdesktop/9.3/… –  Dan Patterson Apr 14 '11 at 19:53
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5 Answers

up vote 6 down vote accepted

You can clip a raster to an irregularly shaped polygon (following the polygons geometry) using the tool you tried before, Clip.

Scrolling down a little further in your screenshot, click the checkmark to enable Clipping Geometry (see image). You should have this available at v9.3; This screen is from 9.3.1

clip raster to irregular polygon, enable clipping geometry

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HA!! Hey SaultDon. I didn't even see that there was a scroll bar on the side of the clip window. It's now time to go home (where I live anyway), and I've used the buffer method posted by "celenius". There is no analytical component to consider here. I was just trying to hide everything around my site (purely a graphical exercise). Let me say .... what an ugly looking figure too. Just for argument sake, I will test this tomorrow provided I don't get bombarded with work. –  Dano Apr 14 '11 at 21:03
    
..... and let me also say that I am disappointed with myself for NOT thinking of the buffer idea!! It never ceases to amaze me how many approaches there can be to solve the same problem, depending on how ones brain is wired. Have a good evening all. –  Dano Apr 14 '11 at 21:06
    
It worked!! I had a slow day, so Itried it out (just for argument sake). Thanks SaultDon –  Dano Apr 19 '11 at 19:09
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Could you create a large buffer outside the object, and then fill this buffer with a white color?

It sounds like you just need a graphical way of hiding the image, rather than something that allows you to perform a calculation.

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Yes ..... I like it!!! I am in a rush. this will certainly suffice on a timeline!!! Thank you –  Dano Apr 14 '11 at 20:03
    
@ everyone -- thanks guys!!! Lots of excellent suggestions!! The buffer is the quickest way. I was going to do the Photoshop thing (thanks Brad & mwalker). Buffer it is. –  Dano Apr 14 '11 at 20:05
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I'd paint all the pixels you don't want to see in white (or another color) and then set that color to be the transparent color in the raster.

You won't need to re-georeference the photo since you have not changed its size or position.

Not 100% sure on the steps to do so in ArcView but I'm pretty sure it can be done.

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Ah yes, but I don't want to lose my original air photo. I will need to save the modified image to another file name. That said, will this not result in a loss of spatial reference info? If I went in (in windows not catalog) and copied all the file extensions from the original GeoTiff (.aux, .xml, etc), and renamed them the same name as the new "clipped" image, the spatial referencing should take hold .... right? Nonetheless, this seems like an enormous waste of time. There must be a tool that'll do this in ArcView?? –  Dano Apr 14 '11 at 19:15
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Yep, copying the auxiliary files will let you keep the spatial reference. And yep, it's a pretty big waste of time - hopefully someone else has a better answer. –  mwalker Apr 14 '11 at 19:59
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Do you have Spatial Analyst?

Is there a "Clip Raster" tool in the Toolbox in version 9.3? ArcToolbox->Data Management Tools -> Raster -> Raster Processing -> Clip

If I remember correctly (it's been a while since i used 9.3) There used be an option to set a Mask on the Spatial Analyst so you could export a raster and it would be clipped to the "Mask" layer.

Without Spatial Analyst? I am not 100% sure. I think the Mosiac Raster tool was avaialble without Spatial Analyst. Not that you need to mosiac but if the mask is set in environmets it might just work. THe tool is also somewhere under Data Management Tools.(in 9.3 it was a model i beleive, in version 10 it's a tool) Can you set a Mask in "Environments" without Spatial Analyst? You might be able to. I think it's under Raster Analysis in Environment Settings.

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No, not yet. I start a new position at the beginning of next month, and I will have Spatial Analyst there. I used the exact tool you've suggested at the top Jakub (Clip Raster). As for the second suggestion, I don't see anything under the environment settings. I'll just head into Photoshop I guess. Thanks for the suggestions. –  Dano Apr 14 '11 at 19:36
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What you need is to draw a graphic in your document with the image placed in it.
select the document properties (right click on the layers and select properties)

properties

Then select the data frame tab> clip options>clip to shape>specify the selected graphic.

clip2shp

If you need to you can set that up in a layout and print it to a graphic format. like jpg or tiff.

By the way, all raster images require a rectangular boundary. If you have a clipped (not really the acurate terminology) or masked image it is ussually just masked in the software and or document you do the masking in. it is an object used to "block" the rest of the image from print/view.

In order to actually clip an image you would need to output your image with a mask appied and tell the output software to assign nodata values to the area outside. Then you would still need to either assign transparency or nodata as no color when you use the same image in another software or document.

PCI Geomatics example

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Hey Brad -- I have a project manager waiting for product, so I'm going to have to try these suggestions out later (appreciated greatly however!!). If I do what I suggested in response to "mwalker", (going with the PhotoShop route), it should work right? –  Dano Apr 14 '11 at 19:49
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yes you would just want to do that on a copy –  Brad Nesom Apr 14 '11 at 19:54
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