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Turning a tiff back into an elevation grid

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#1
Charles Syrett

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Say I've opened an elevation grid in Photoshop as a tiff and done some editing to eliminate artifacts, terracing, etc. Is there any app (preferably not Arc) that will allow me to import the edited tiff and assign elevations based on the grayscale pixel values, to create a new elevation grid (or surface, or DTM, whatever you want to call it)? Something like (for example): darkest pixel value is 237 feet, lightest is 573 feet, and everything in between is a linear progression. The idea is to edit an elevation grid using Photoshop tools and then recreate the edited grid for contouring etc. Any suggestions?

Thanks!

Charles Syrett
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#2
Hans van der Maarel

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It's not something I'm often doing, but iirc VNS (Visual Nature Studio) can import Geotiffs, then assign an elevation range to them and grid a surface.

Global Mapper offers the same functionality, haven't been able to succesfully get that working though but that may be a data issue.
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#3
Charles Syrett

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I see VNS is "only" $3,000.00! I tried this in Global Mapper, but couldn't see any way to do it. I'm not sure what you mean by a "data issue", since we're just dealing with grayscale pixels...?

Charles Syrett
Map Graphics
http://www.mapgraphics.com


It's not something I'm often doing, but iirc VNS (Visual Nature Studio) can import Geotiffs, then assign an elevation range to them and grid a surface.

Global Mapper offers the same functionality, haven't been able to succesfully get that working though but that may be a data issue.



#4
Hans van der Maarel

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I see VNS is "only" $3,000.00! I tried this in Global Mapper, but couldn't see any way to do it. I'm not sure what you mean by a "data issue", since we're just dealing with grayscale pixels...?


After importing, you can go to the Control Centre, select the layer that holds your TIFF, then click the Options button and go to the Alter Elevations tab where you have the option to set min and max values.

The "data issue" I was referring to is the fact that I'm not entirely sure about the quality of the one file I tried this on. I'm not getting the results I expect, but I do remember 'tinkering' with this file 2 years ago and I'm not sure what I did back then that might have been destructive :)
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#5
Charles Syrett

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I guess I ran into the same issue that you did, because there's no Alter Elevations tab showing up. Presumably that's because there are no elevations to alter. I'm trying to assign elevations, rather than alter them. :rolleyes:

Charles Syrett
Map Graphics
http://www.mapgraphics.com


After importing, you can go to the Control Centre, select the layer that holds your TIFF, then click the Options button and go to the Alter Elevations tab where you have the option to set min and max values.

The "data issue" I was referring to is the fact that I'm not entirely sure about the quality of the one file I tried this on. I'm not getting the results I expect, but I do remember 'tinkering' with this file 2 years ago and I'm not sure what I did back then that might have been destructive :)



#6
Hans van der Maarel

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I guess I ran into the same issue that you did, because there's no Alter Elevations tab showing up. Presumably that's because there are no elevations to alter. I'm trying to assign elevations, rather than alter them. :rolleyes:


When you open it, it should ask whether you want to process it as elevation or a regular tiff. I suppose that only works with greyscale images though, so maybe that's what's amiss.

It then assigns bogus values for the elevation, which you can set to whatever it should be through the Alter Elevations tab. This is all with 9.03, check you have the latest update.
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#7
Charles Syrett

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Turns out the tiff has to be 16-bit. Here's what Mike at Global Mapper said:

"If you can export the TIFF as a 16-bit grayscale TIFF file then you can bring it into Global Mapper as an elevation TIFF. Once you have the data as an elevation layer, you can provide a scale factor and offset to adjust the range as desired by opening the Control Center, pressing Options, then going to the Adjust Elevations tab and entering the correct information.

"If you can only get an 8-bit grayscale TIFF out of Photoshop, you can bring that into Global Mapper, then immediately export that to a 8-bit grayscale BIL file, then load that BIL file back in as an elevation layer and apply the same steps as above."

Charles Syrett
Map Graphics
http://www.mapgraphics.com


When you open it, it should ask whether you want to process it as elevation or a regular tiff. I suppose that only works with greyscale images though, so maybe that's what's amiss.

It then assigns bogus values for the elevation, which you can set to whatever it should be through the Alter Elevations tab. This is all with 9.03, check you have the latest update.



#8
Matthew Hampton

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I just brought an RGB tif of a DEM back into ArcGIS and made a hillshade of it in Spatial Analyst - after modifying the tif (DEM export) in Photoshop. The data were initially floating point, but became an 8-bit "greyscale" RGB. I think that's why there's terracing in the attached image(s).

The question remains - VNS $3k, ArcGIS Arcview w/Spatial $4k.

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#9
Charles Syrett

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Cute terrain features, Matthew, looks like you had some fun doing it! :lol:
Actually,there's even a convoluted way to do this on a Mac using MFWorks and MacDEM, but I ended up using Global Mapper.

Charles Syrett
Map Graphics
http://www.mapgraphics.com


I just brought an RGB tif of a DEM back into ArcGIS and made a hillshade of it in Spatial Analyst - after modifying the tif (DEM export) in Photoshop. The data were initially floating point, but became an 8-bit "greyscale" RGB. I think that's why there's terracing in the attached image(s).

The question remains - VNS $3k, ArcGIS Arcview w/Spatial $4k.



#10
Matthew Hampton

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Cute terrain features, Matthew, looks like you had some fun doing it! :lol:


I can't quite explain how those terrain features ended up there... B)

I was actually curious to know if Spatial Analyst's hillshading operation could read greyscale RGB values in place of actual elevations from a DEM. It looks like it can.

Not too sure if that's a very high request on a feature-list, but I sometimes like to try and flex the capabilities of ArcGIS. I sometimes even try and make a map with it... :lol:

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#11
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maybe you should focus on improving your handwriting too? :)
Hugo Ahlenius
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