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Shaded Relief help

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#1
mikeb226

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Ok, so, I've been reading up on a lot of the tutorials scattered on the web dealing with shaded relief and photoshop.

The series of events to get the desired effect is roughly the same, however, the source of the DEM is also the same. For example, most of the tutorials use the freely available NED data from the USGS.

The state I live in, Pennsylvania, recently undertook a five year project to provide statewide orthophotography, LiDAR, and base imagery.

From the LiDAR, DEMs and 2ft contours were derived.

All being freely available online (google pasda).

Having received the DEMs from the lidar, it appears that the process to create good relief is slightly different.

My question is this: have any of had to change the way you create shaded relief because of the high accuracy of DEM's derived from lidar?

attached is an example of what I'm seeing, using the typical steps in photoshop to get shaded relief.

I can't figure out a good way to get rid of the terracing without compromising the clarity of the relief. I've tried the median/blur/unsharp mask trick 20 different ways but to no avail.

Any suggestions?

Thanks!

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#2
aug_aug

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Isn't the terracing a result of the way you're processing the LiDAR data? Are you creating the DEM from xyz data, or are you downloading a finished DEM model/tile from somewhere? If they're available you can download the bare earth data sets and interpolate/process yourself (kriging/IDW), smoothing out the "terraces".

I'm not sure I understand your exact workflow, but the terrace issue should probably be resolved prior to PS import/manipulation.

Hope that helps.

#3
Matthew Hampton

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I have a hunch that you are using 8-bit integer data which results in the terracing. The best solution would be to use 16 bit floating point data. If you have become familiar with many of the tutorials online – I think you might look for 16-bit information.

Michael is right to infer that there's nothing wrong with your processing, but that the data you are using is the problem. Using your existing data, you might try and upsample the data in PS, then run a smoothing filter on it and resample it again.

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#4
mikeb226

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aha, that could be the problem.

The DEM I'm using has been processed somewhere else.

here's where they are available:
ftp://pamap.pasda.psu.edu/

Specifically, here's the tile from the above example:
ftp://pamap.pasda.psu.edu/pamap_lidar/cyc...1280PAN_dem.zip
Warning: 18mb zip file

if you have the time, take a look. I've been trying to use these tiles in different programs such as 3DEM and MicroDEM and ArcGIS, but have not been getting the sort of results I expect from using USGS DEMs.

I confess I can't tell what's different.

#5
Hans van der Maarel

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I'm not sure whether this has anything to do with your terracing, but the TIFF appears to be 32-bit greyscale. Photoshop CS3 definately had an issue with that...

Anyway, loaded it up into Global Mapper and got this result:
Attached File  dem_in_global_mapper.jpg   120.44KB   97 downloads

No terracing. No pre-processing needed either by the way. So my gut feeling is that one of the steps you're doing to get to your result effectively reduces the bit-depth of the image, which reduces the number of unique elevation values available, resulting in terracing.
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#6
aug_aug

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I grabbed a random file from the ftp, you want to use these files from that ftp site and then create a hillshade "67001280PAN_dem.tif"

Attached File  lidar_PA.jpg   385.66KB   107 downloads

This is all prior to PS. I'm not sure why those other files have the banding, and it is embedded in the raster/dem. There doesn't appear to be any readme file explaining the different LiDAR data types available, or how they're organized, etc. so I guess you're on your own. I would try to google the name of the project, usually when this data goes public you're able to track down a pdf of the actual project report which includes spatial info, flight lines, dates, etc.

Again, I hope this helps.

Michael

#7
frax

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Mikeb - when you load up the initial raster in PS, do you see the stair-steps then (before applying the light effect) - if so, you need to blur/smooth it before applying the shading.

Oh - and there shouldn't be any difference if it is LIDAR, compared to other forms of DEM, as long as it is a raster image with elevations.
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#8
mikeb226

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Thank you guys so much for your guidance.

I think I know where the problem is. I'm attempting to do the relief shading in photoshop CS3. But, as Hans stated, photoshop does not like the raw images. So I load up the image in ArcMap, pick my out put size, then export out as a 24-bit rgb tiff with lzw compression.

I think that step is the problem.

So, my question is this: in order to do the shaded relief and be able to work with it in photoshop, should I do the shading in something like global mapper, then export it out? Or is there a way to import 32bit greyscale images into ps?

#9
Hans van der Maarel

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Thank you guys so much for your guidance.

I think I know where the problem is. I'm attempting to do the relief shading in photoshop CS3. But, as Hans stated, photoshop does not like the raw images. So I load up the image in ArcMap, pick my out put size, then export out as a 24-bit rgb tiff with lzw compression.

I think that step is the problem.

So, my question is this: in order to do the shaded relief and be able to work with it in photoshop, should I do the shading in something like global mapper, then export it out? Or is there a way to import 32bit greyscale images into ps?


Yes, converting it back down to 24 bit is introducing the problem (lzw compression really shouldn't make any difference, other than filesize).

Based on what I've seen yesterday, but also somewhat depending on what you're intended end result is, doing the shading in an application that supports 32-bit Tiff's and then exporting the result back to Photoshop would be preferrable. However, as Michael's rendering shows, there's a lot of noise (buildings, trees) in the LIDAR data, so do keep that in mind when you're considering whether or not to use this for shaded relief.
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#10
mikeb226

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Thank you both for your help.

I think I know what my plan of attack will be.

As for the final product, I am making a wall map showing the physical features of Erie County, Pennsylvania.

I was going to use the DEMs from the lidar to do a shaded relief of the whole county. The DEMs came to us in 289 tiles, 40mb each, covering the county. Combining them into a raster dataset has been problematic. Mostly, I think due to the file size.

So, I decided to do a shortcut and use the USGS NED DEMs for the county view and then use the lidar DEMs in callouts to highlight some unique features.

In the meantime, I have tracked down the author of a presentation I attended at the PA GIS Conference about using slope-shape to show terrain relief. I'm gonna post that in another post for all to see, though.

Also, when I get to a good point in the map, I'll post it in the gallery for everyone to critique.

Thanks again!

#11
mikeb226

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oh, and here's the metadata for those DEMs:

http://www.pasda.psu...a/PAMAP_DEM.xml

#12
Mike Boruta

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So, my question is this: in order to do the shaded relief and be able to work with it in photoshop, should I do the shading in something like global mapper, then export it out? Or is there a way to import 32bit greyscale images into ps?


If you do want to bring a 32bit greyscale tiff into photoshop (CS4) try this:

1. Open file in photoshop, accept the default "assign working gray: dot gain 20%" profile (I honestly don't know what this does, if anything)
2. The image will appear as all white. Change the image mode from 32bit to 16bit. When the "HDR Conversion" dialog comes up, change the method to "Equalize histogram"

I've used this to manipulate USGS tif DEMs before bringing them back into other software (NSD, Arc) for shading/rendering.

I would agree with Hans (do the relief shading in another app, then bring that into photoshop) but, if wanted to make a hillshade in photoshop you could do it this way without having to export the dem out of arc. However, when you use the "Render - Lighting Effects" filter you do need an 8bit image. I tried it on your file and it looked decent (see attached). Some of the detail seems generalized, but this may be a pro or con when you consider the level of detail in the lidar dem.

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#13
mikeb226

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oh hey, borga, that worked like a charm!

Thanks!

I'm gonna compare this to the method Hans recommended to see what gives me the best results.

Huh, all this time I was using the wrong version of Photoshop.




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