grainy hillshade result
Posted 05 November 2011 - 08:01 PM
I am using a DEM in tiff format (free 30m GDEM ASTER data) to create a terrain base map (for an area appx. 80x50 km) on which I will later add other data.
The plan was to:
1) create a hillshade from the DEM in ArcMap and export image
2) apply desired classes and colour ramp to original DEM and export image
3) overlay both in Photoshop
I see there are numerous topics on how to adjust the hillshading/relief shading for specific needs.. It's all very interesting and I'm looking forward to going through the basics someday (reliefshading.com, shadedrelief.com etc.) and then tweaking the process. BUT at the moment I'm interested in getting my base map, so I can focus on the data that comes on top of it.
I'm quite happy with the initial result, except for the grainy look of the hillshade image. For example, the depression at the top of the image should be flat, but instead looks like shattered glass - giving impression of anything but a flat surface.. I've tried playing around with the settings but had no big success.
Would be happy if anyone could point me to the right direction: should I look into data manipulation before hillshading or leave the data and work on the hillshading process itself? or maybe the data used here is not appropriate for my scale and I should be looking into the photoshop effects?
Thx in advance!
Note: I'm att. images of the original DEM, the DEM after hillshading and the final result from photoshop (not the whole area):
Posted 06 November 2011 - 06:30 AM
The Sun's denoising algorithm looks promising... but I can't make it work.. Using GDAL (via FWTools) I prepare the DEM file as described in the link you've provided (reproject data to projected coordinate system and then convert it to ESRI ASCII grid format).. but when I execute the command to use the algorithm the process crashes (This application has requested the Runtime to terminate it in an unusual way.) I have repeated the whole process with the example data and am successful.. so no idea why it doesn't work with my data..
Still not sure why the initial hillshade result looks like elephant skin ... and not something like (is it poor data quality?):
Posted 06 November 2011 - 07:58 AM
I'd also suggest trying hillshading with some other software (using the same DEM) to be able to compare results. You can also try hillshading and hypsometric tinting in Maperitive (although you won't be able to use ASTER DEM directly, just SRTM) - it never produces such noisy mess (http://maperitive.ne...ypsometric.html).
Posted 06 November 2011 - 09:42 AM
Tom's comparison between manual and automatic shaded relief
Some tools by Bernhard
Daniel's take on things
Hope this helps.
Email: email@example.com / Twitter: @redgeographics
Posted 07 November 2011 - 09:38 AM
The way to correct that, if you're using ArcMap, is to set a z-factor when you run the hillshade tool.
Here's some info from an
Esri Mapping Center post
Posted 07 November 2011 - 05:33 PM
I have now the first result at hand (using more or less default hillshading settings and little noise-median filter in photoshop). Will definitely play more with this as there are tons of advice out there.. but will wait for the main data that comes over it to see which variant will suit best. Will also have to decide between stretched and classified colour ramp..
@Igor: will also try Maperitive, looks very cool. One Q though: if I remember correctly, you wrote somewhere on the maperitive blog that the license for ASTER GDEM data is somehow problematic. Can you please elaborate?
Thanks again to all!
Posted 08 November 2011 - 02:55 AM
One Q though: if I remember correctly, you wrote somewhere on the maperitive blog that the license for ASTER GDEM data is somehow problematic. Can you please elaborate?
By "problematic" I meant the license is much more restrictive than SRTM (which is in Public Domain) and overly complicated, in my view. You cannot redistribute their DEM data or any kind of derivative work that produces a lossless transformation that would allow recovery of the original data (like converting DEM to another format and putting that on some Web server).
You can, however, redistribute hillshadings, 3D renderings and similar derivative work, since it is not possible to reconstruct the original DEM data from such products.
Take a look at https://lpdaac.usgs..../aster_policies (make sure you click on the "Click here for additional GDEM redistribution information.").
One other reason why I didn't include direct ASTER DEM support in Maperitive is because you need to be registered & logged into their website in order to be able to download the data and I wanted the DEM download to run seamlessly for users (like it's in the case of SRTM data). However, if a future version of Maperitive you will be able provide your own DEM GeoTIFF tiles, so you'll be able to use ASTER.
Posted 08 November 2011 - 07:31 AM
Looking forward to the import TIFF support in Maperitive.
Posted 19 November 2011 - 01:12 AM
Layer blending reliefs of differing resolution are a very useful way of maintaining some detail, while making sure the major watersheds, and peaks are not lost in the detail. This is particularly the case in mountainous terrain. Tom has a couple of examples on his site.
Edited by Dale A, 19 November 2011 - 01:18 AM.
Posted 14 January 2012 - 08:32 PM
I was wrong about Z factor, but I will follow Tom guide.... he is the man!
Thanks to all
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