Converting an image to a shapefile

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12-03-2013 07:17 AM
CaiLadd
New Contributor
I'm working on digitising aerial images of saltmarshes onto ArcGIS, so that I can measure change in extent over time.

To do this, I had a georeferenced image loaded on Adobe Photoshop Elements (figure 1). There, I extracted the 'saltmarsh', and subsequently re-georeferenced that image back into ArcGIS 9, but this time with only the parts that I'm interested in (figure 2).

Now, I want to convert all the greenish stuff into a shapefile. What is the best way to do this? I didn't want to create a new polygon by hand because as you can see, the structure is rather complex and it would be time consuming to draw it accurately (I have many more images to process after this).

Any ideas? Your help would be really appreciated?

Thanks,
   C

[ATTACH=CONFIG]29530[/ATTACH]
Figure 1: Saltmarsh image.
[ATTACH=CONFIG]29531[/ATTACH]
Figure 2: Saltmarsh aera removed from background - I now want to convert this section of image into a shapefile. How do I do this?
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8 Replies
by Anonymous User
Not applicable
Original User: AngelynDavis

Depending on your license, I believe there is a geoprocessing tool that can do this for you. How are you extracting the saltmarsh area?
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michaelcollins1
Occasional Contributor III
Try Conversion Tools\From Raster\Raster to Polygon tool, use Simplify Polygons, then Dissolve them.
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by Anonymous User
Not applicable
Original User: cailadd

Depending on your license, I believe there is a geoprocessing tool that can do this for you. How are you extracting the saltmarsh area?


Yes, that's actually one of the problems I have; I've found guides on using Raster Domain tool under 3D Analyst Tool/Conversion, however at the moment I've not got the licence allowing me to use it. I recently asked the university for an upgrade to ArcGIS 10.1 with full licence and this morning they should be installing it on my computer! I'll update when that happens.

As for extracting the saltmarsh area, I used Adobe Photoshop Elements. You can strongly contrast the image to emphasise the 'green' saltmarsh and its 'white' sandy surroundings, and using the quick selection and magic wand tool, you can crop out the sand leaving only the saltmarsh behind.
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CaiLadd
New Contributor
Try Conversion Tools\From Raster\Raster to Polygon tool, use Simplify Polygons, then Dissolve them.


Thank you very much! I've had a go, and the results look promising - not quite the resolution I hoped for, but it's still very good (fig. 1). I'll have a play around with improving it and then report back.

What did you mean by "dissolve"?

[ATTACH=CONFIG]29555[/ATTACH]
Figure 1: Raster to polygon
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by Anonymous User
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Original User: pmcatnip

Dissolve is used to combine adjacent polygons into one polygon (it "dissolves" the internal lines between them).  Looks like your output may already be dissolved.  Dunno why it pixelated that badly.  I've never seen polygon output that rough.
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by Anonymous User
Not applicable
Original User: AngelynDavis


What did you mean by "dissolve"?


Click on "Geoprocessing" on your toolbar in ArcMap and then select "Dissolve".
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CaiLadd
New Contributor
Dissolve is used to combine adjacent polygons into one polygon (it "dissolves" the internal lines between them).  Looks like your output may already be dissolved.  Dunno why it pixelated that badly.  I've never seen polygon output that rough.


Ok. I'll do that if necessary.

I've thought about that, maybe its because the image had different shades of green and the GIS tool couldn't deal with it. I've made the saltmarsh black, so when it gets converted to polygon it might look better. Will post when I've done this.
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by Anonymous User
Not applicable
Original User: cailadd

Click on "Geoprocessing" on your toolbar in ArcMap and then select "Dissolve".


Ok, thanks!
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