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Contours Shape file from Global Mapper to Terragen - Help with banding

Started by Tudor, June 13, 2016, 10:59:01 PM

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Tudor

June 13, 2016, 10:59:01 PM
Hello
I'm finally able to commit some more time to this project.
I've made a small amount of progress only to take a few steps back.
Global Mapper is able to generate .ter files from Shape files.
I have figured out how to do this (although I should add that Global Mapper is a disaster from UX stand point)
The problem is when I pull the files in and render them out I see banding correlated to the contour lines

Questions.
1. Does anyone know how to smooth out the lines in Global Mapper so this doesn't happen?
2. Does anyone know how to get rid of the banding without wiping out the detail in the landscape?

Any help as always would be greatly appreciated.
Regards,
Tudor

ps.  Pics attached show 3d top view in Global Mapper (blue) as well as the contours.  The Terragen render shows the same lake and you can see the banding which correlates to the contour lines.

ajcgi

#2
June 14, 2016, 06:37:40 AM
Ah this is very interesting. I've wondered about this...
The only time I've had banding is when exporting GeoTiff and using inadequate bit depth.

Tudor

#3
June 14, 2016, 06:51:38 AM
I have also seen this banding in GeoTIFFs generated from similar source files but I had assumed going straight from Shape files to a .ter I wouldn't have the same problem.

Are .ter files raster based?

Am I better off going back to GeoTIFF or is there an actual advantage to a .ter?

Oshyan

#5
June 15, 2016, 02:47:38 PM
TER is a raster format (bitmap, pixels). What you're seeing is a very literal representation of what your contour lines represent. There is literally no more detail than that in the contours, as far as I can see. Any additional "detail" (or smoothness, for example interpolation between lines) would be a guess basically. Literal interpolation. It's a function Global Mapper should have, so I would look for it, and it will give you a smoother, non-stepped result. But again if you look at the output it looks like a literal interpretation of the contour map input.

- Oshyan

Tudor

#6
June 15, 2016, 03:07:01 PM
I was able to resolve the issue last night with some help from the Global Mapper community forum.
For those that end up having a similar problem I ended up exporting GeoTIFF file with using an elevation 32-bit floating-point samples.  This averaged out the area between the contour lines and solving the problem.
Now that I have the base landscape done I can finally get back to the work of setting up the scene.

Thanks again to everyone who responded.
I appreciate all the help.

Regards,
Tudor

Oshyan

#7
June 15, 2016, 03:34:57 PM
Glad to see you resolved it. It's strange that simply exporting to a different format solved it though. There is no inherent limitation in TER format that should cause those issues.

- Oshyan

Tudor

#8
June 15, 2016, 03:38:42 PM
I think the problem might be with Global Mapper ... assuming I truly understand what I did.
Certain export file formats allow certain options...
I'll take a look again to double check this.

It is very possible that we are dealing with user error.
I'm very good at breaking things.  Unfortunately.

Cheers,
Tudor

tjhb

#9
June 15, 2016, 07:27:14 PM
Hi Tudor. I thought I'd touch base with you here as well (my first Terragen post) and explain a bit more the banding problem.

Thanks to AP's link to the wiki page on the .TER format we can confirm the cause: that .TER only stores integer elevation values.
http://forum.globalmapperforum.com/discussion/comment/48039/#Comment_48039

It's hard to know why that design decision was made (maybe it can be revisited), but for now it makes .TER an inadequate format for storing and exchanging DEMs.

Your data was perfectly smooth before export. It's only because Global Mapper had to round values to the nearest integer to fit the .TER format that banding was introduced.

Exporting to 32-bit floating-point GeoTIFF instead preserved floating-point values--only single-precision, but good enough to preserve smoothness.

Luckily Terragen can read FP32 GeoTIFFs perfectly, so this looks like the format of choice for exporting GIS data for use in Terragen.

Tim

Oshyan

#10
June 25, 2016, 02:24:50 AM Last Edit: June 25, 2016, 02:26:55 AM by Oshyan
Hi Tim, welcome!

For GIS data GeoTIFF is definitely the format of choice in Terragen. However the TER format is 16 bit, I believe, so it too should work (and has been successfully used for converted DEM data in the past, for example my very popular 3m resolution St. Helens files many years ago).
So you map the data to fit into the 16 bit space and then use a scale value to rescale it on load to the correct dimensions. It's certainly not as good as 32 bit, but banding was rarely a problem in general TER files. It's only when you try to use it linearly, 1:1, that problems come in I believe.
http://planetside.co.uk/wiki/index.php?title=Terragen_.TER_Format

Admittedly the TER format has been misunderstood or "incorrectly" implemented on occasion by other applications, so it may be a flaw in the format. That being said it may be possible for you to improve GlobalMapper's TER output. But I may also may be talking a bit beyond my knowledge level as a non-coder myself. ;)

- Oshyan
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