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Terrain creation procedure in vpb


 
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vijeesh
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Joined: 25 Dec 2010
Posts: 36

PostPosted: Sat Dec 25, 2010 9:44 am    Post subject:
Terrain creation procedure in vpb
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Hi,
I'm new to vpb/osg. I have a tiff file which is only 5x5km. Also I dowloaded the srtm hgt data from dds.cr.usgs.gov. I want to create a terrain out of these two files. I tried osgdem with --xx 10 --yy 10 as specified in vpb tutorial. Terrain is created but when it is loaded, Only a small portion at one corner of the terrain is having the elevation data and rest are all flat. What could be the reason. Also I would like to know what exactly --xx --yy argument specifies. I'm a new bie in the terrain modelling. Also I want to know how to check whether the tiff file is actually georeferenced or not. Please help me

...


Thank you!

Cheers,
Vijeesh
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Martin Naylor
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PostPosted: Wed Dec 29, 2010 3:10 pm    Post subject:
Terrain creation procedure in vpb
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Hi,
Not sure I can answer all the questions:
But they should be geo referenced(srtm data), you can probably omit the xx
and yy parameters. Believe they just specifiy the coordinates for manual
placement (if the file is not georeferenced).

Just try osgem -d nameofheightfieldfile -t nameoftexture -o terrain.ive

Providing the texture is georeferenced you should be ok.
Dont forget to add the --geocentric when using osgdem, providing you want a
round earth if not leave it out for flat terrain.
You can use gdalinfo to find the format the tiff files are in, I use FWTools
for windows.

Hope it helps a little.


Martin.





-----Original Message-----
From:
[mailto:] On Behalf Of Vijeesh
Theningaledathil
Sent: 25 December 2010 09:46
To:
Subject: Re: [vpb] Terrain creation procedure in vpb

Hi,
I'm new to vpb/osg. I have a tiff file which is only 5x5km. Also I dowloaded
the srtm hgt data from dds.cr.usgs.gov. I want to create a terrain out of
these two files. I tried osgdem with --xx 10 --yy 10 as specified in vpb
tutorial. Terrain is created but when it is loaded, Only a small portion at
one corner of the terrain is having the elevation data and rest are all
flat. What could be the reason. Also I would like to know what exactly --xx
--yy argument specifies. I'm a new bie in the terrain modelling. Also I want
to know how to check whether the tiff file is actually georeferenced or not.
Please help me

...


Thank you!

Cheers,
Vijeesh

------------------
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http://forum.openscenegraph.org/viewtopic.php?p=35166#35166




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asierra
Newbie


Joined: 05 Nov 2010
Posts: 8

PostPosted: Wed Dec 29, 2010 5:15 pm    Post subject:
Terrain creation procedure in vpb
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Hi,

The data should have geographic metadata so don't use -xx -yy. Have
you tried gdalinfo with your data? (part of gdaltools wich yoo need
installed for VPB proper working)

Reqards,

-- A.


On Sat, Dec 25, 2010 at 3:45 AM, Vijeesh Theningaledathil
<> wrote:
Quote:
Hi,
I'm new to vpb/osg. I have a tiff file which is only 5x5km. Also I dowloaded the srtm hgt data from dds.cr.usgs.gov. I want to create a terrain out of these two files. I tried osgdem with --xx 10 --yy 10 as specified in vpb tutorial. Terrain is created but when it is loaded, Only a small portion at one corner of the terrain is having the elevation data and rest are all flat. What could be the reason. Also I would like to know what exactly --xx --yy argument specifies. I'm a new bie in the terrain modelling. Also I want to know how to check whether the tiff file is actually georeferenced or not. Please help me

...


Thank you!

Cheers,
Vijeesh

------------------
Read this topic online here:
http://forum.openscenegraph.org/viewtopic.php?p=35166#35166




Attachments:
http://forum.openscenegraph.org//files/osg_first_233.jpg






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vijeesh
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Joined: 25 Dec 2010
Posts: 36

PostPosted: Thu Dec 30, 2010 4:43 am    Post subject:
terrain generation using osgdem
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Hi Martin
Thanks a lot. That image was georeferenced. So when i removed -xx and --yy as you told, I got the terrain. But my next question is my imagery file is only covering a small area and the elevation data is 3 arc sec srtm hgt file for 1degx1deg . So I'm getting the terrain with imagery on some portion and the rest is white. How to limit the terrain so it covers only the area referenced in the image file. Also the quality of the texture is very poor compared to the original tiff file. Is it because of the image resolution is low?.


Thank you!

Cheers,
Vijeesh
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Martin Naylor
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PostPosted: Thu Dec 30, 2010 9:10 am    Post subject:
Terrain creation procedure in vpb
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HI Vijeesh,
Not sure about that one, I have always generated a full earth.
If you do an osgdem --help you will see some options -gb and -ge could be
the ones you need?
If the initial image resoulution is low then I suspect that is the problem.
Although it could be worth making sure you run gdal_translate on the image
and gdaladdo, see if that helps?
Also the amount of levels will determine the amount of LOD to generate, have
a look at the -l option.

Let us know how it goes, I am still learning osgdem!

Cheers

Martin.

-----Original Message-----
From:
[mailto:] On Behalf Of Vijeesh
Theningaledathil
Sent: 30 December 2010 04:43
To:
Subject: Re: [vpb] Terrain creation procedure in vpb

Hi Martin
Thanks a lot. That image was georeferenced. So when i removed -xx and --yy
as you told, I got the terrain. But my next question is my imagery file is
only covering a small area and the elevation data is 3 arc sec srtm hgt
file for 1degx1deg . So I'm getting the terrain with imagery on some portion
and the rest is white. How to limit the terrain so it covers only the area
referenced in the image file. Also the quality of the texture is very poor
compared to the original tiff file. Is it because of the image resolution is
low?.


Thank you!

Cheers,
Vijeesh

------------------
Read this topic online here:
http://forum.openscenegraph.org/viewtopic.php?p=35227#35227









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vijeesh
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Joined: 25 Dec 2010
Posts: 36

PostPosted: Fri Dec 31, 2010 10:08 am    Post subject:
Terrain creation procedure in vpb
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Hi Martin,

Thanks for your information, I'll try with better resolution imagery






Thank you!

Cheers,
Vijeesh
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J.P. Delport
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PostPosted: Mon Jan 03, 2011 10:56 am    Post subject:
Terrain creation procedure in vpb
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Hi,

I suggest you manipulate your input data using gdal tools and then just
stick the results into vpb. Trying to align and crop data in vpb is
difficult.

jp

On 31/12/10 12:08, Vijeesh Theningaledathil wrote:
Quote:
Hi Martin,

Thanks for your information, I'll try with better resolution imagery






Thank you!

Cheers,
Vijeesh

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http://forum.openscenegraph.org/viewtopic.php?p=35238#35238








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vijeesh
User


Joined: 25 Dec 2010
Posts: 36

PostPosted: Fri Jan 07, 2011 11:38 am    Post subject:
Terrain creation using vpb
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Hi,

Now when I increased number of LODs, the terrain became OK. and I patched the rest of the area using a generic image file. Now a new problem occurs. I used SRTM 3 arc sec data (1degx1deg)hgt. When I place my camera near the ground and displayed the eye position, x and y are matching with lat/long. But the z value is giving 0.00xxx. Why This happens?. what is the unit of z axis in this context? please let me know.


Thank you!

Cheers,
Vijeesh
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