Problem creating heightfield from JPL OnEarth server

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Evan Andersen Evan Andersen
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Problem creating heightfield from JPL OnEarth server

I'm trying to access the NED 1 arc-second elevation data hosted on the NASA JPL OnEarth server using their tile scheme.  The source of the .earth file I'm using is included below.  I can download elevation tiles fine, but when I zoom in past the first couple of LOD's I start to see a lot of strange artifacts in the terrain.  If I look at the wireframe I can see parts of it that fold over the top or underneath other parts of the terrain.  Any ideas on what might be causing this?

Evan


<map name="JPL NED 1" type="geocentric">
 
  <heightfield name="Continental US Elevation" driver="wms">
    <url>http://onearth.jpl.nasa.gov/wms.cgi</url>
    <layers>us_ned</layers>
    <style>feet_short_int</style>    <format>png</format>
    <tile_size>300</tile_size>
    <elevation_unit>ft</elevation_unit>
  </heightfield>

  <vertical_scale>8</vertical_scale>

  <skirt_ratio>0.01</skirt_ratio>
 
</map>
jasonbeverage jasonbeverage
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Re: Problem creating heightfield from JPL OnEarth server

Hi Evan,

Try changing your tile_size to something like 32 or 64.  Setting it to 300 is making a 300x300 terrain tile which is a ton of geometry and could be causing issues with their server.  If that still doesn't fix the issue, try using tiff instead of png as the format, sometimes it works better with that server.  Also, keep in mind that that JPL server goes down constantly and refuses requests all the time, so it might not be the most reliable server to hit.

Also, what version of OSG are you using?

Thanks,

Jason

On Tue, Aug 18, 2009 at 3:39 PM, Evan Andersen (via Nabble) <[hidden email]> wrote:
I'm trying to access the NED 1 arc-second elevation data hosted on the NASA JPL OnEarth server using their tile scheme.  The source of the .earth file I'm using is included below.  I can download elevation tiles fine, but when I zoom in past the first couple of LOD's I start to see a lot of strange artifacts in the terrain.  If I look at the wireframe I can see parts of it that fold over the top or underneath other parts of the terrain.  Any ideas on what might be causing this?

Evan


<map name="JPL NED 1" type="geocentric">
 
  <heightfield name="Continental US Elevation" driver="wms">
    <url>http://onearth.jpl.nasa.gov/wms.cgi</url>
    <layers>us_ned</layers>
    <style>feet_short_int</style>
    <format>png</format>
    <tile_size>300</tile_size>
    <elevation_unit>ft</elevation_unit>
  </heightfield>

  <vertical_scale>8</vertical_scale>

  <skirt_ratio>0.01</skirt_ratio>
 
</map>


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Evan Andersen Evan Andersen
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Re: Problem creating heightfield from JPL OnEarth server

Jason,

I'm trying to make my tile access match the server's pre-cached tile access pattern as described at http://onearth.jpl.nasa.gov/tiled.html and http://onearth.jpl.nasa.gov/wms.cgi?request=GetTileService.  The description of the layer I'm trying to access is at the bottom of the document returned by the GetTileService request.  For the data source I'm trying to access the image is a 300x300 png containing 16 bit signed int values.  Deviating from this access pattern causes the jpl server to go through the much slower and less reliable wms access route.  The .earth file I posted seems to make the wms plugin only access the pre-cached tiles and I don't ever get refused connections.  Using the example jpl file in the osgEarth tests directory I can't ever seem to get much of anything from the server.

As for OSG version, I just compiled from the trunk last Friday, so it's pretty current.

Thanks,
Evan

On Tue, Aug 18, 2009 at 2:29 PM, jasonbeverage (via Nabble) <[hidden email]> wrote:
Hi Evan,

Try changing your tile_size to something like 32 or 64.  Setting it to 300 is making a 300x300 terrain tile which is a ton of geometry and could be causing issues with their server.  If that still doesn't fix the issue, try using tiff instead of png as the format, sometimes it works better with that server.  Also, keep in mind that that JPL server goes down constantly and refuses requests all the time, so it might not be the most reliable server to hit.

Also, what version of OSG are you using?

Thanks,

Jason

On Tue, Aug 18, 2009 at 3:39 PM, Evan Andersen (via Nabble) <[hidden email]> wrote:
I'm trying to access the NED 1 arc-second elevation data hosted on the NASA JPL OnEarth server using their tile scheme.  The source of the .earth file I'm using is included below.  I can download elevation tiles fine, but when I zoom in past the first couple of LOD's I start to see a lot of strange artifacts in the terrain.  If I look at the wireframe I can see parts of it that fold over the top or underneath other parts of the terrain.  Any ideas on what might be causing this?

Evan


<map name="JPL NED 1" type="geocentric">
 
  <heightfield name="Continental US Elevation" driver="wms">
    <url>http://onearth.jpl.nasa.gov/wms.cgi</url>
    <layers>us_ned</layers>
    <style>feet_short_int</style>
    <format>png</format>
    <tile_size>300</tile_size>
    <elevation_unit>ft</elevation_unit>
  </heightfield>

  <vertical_scale>8</vertical_scale>

  <skirt_ratio>0.01</skirt_ratio>
 
</map>




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jasonbeverage jasonbeverage
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Re: Problem creating heightfield from JPL OnEarth server

Hi Evan,

It looks like it has something to do with the say the skirts are being rendering in osgTerrain.  Setting the skirt ratio to 0 seems to cause the weird connecting lines to go away for me.

However I quickly start to get OpenGL out of memory errors due to the huge amount of geometry on each tile.  At some point it would be nice if osgEarth had kind of a meta-tiling scheme where we could use datasources like this but scale the actual rendered tiles down to something more manageable like 32x32 or 64x64 on the fly.

You might try asking about the terrain skirt issue on the osg mailing list, I'm not sure what the issue would be right off hand.

Thanks,

Jason

On Tue, Aug 18, 2009 at 4:48 PM, Evan Andersen (via Nabble) <[hidden email]> wrote:
Jason,

I'm trying to make my tile access match the server's pre-cached tile access pattern as described at http://onearth.jpl.nasa.gov/tiled.html and http://onearth.jpl.nasa.gov/wms.cgi?request=GetTileService.  The description of the layer I'm trying to access is at the bottom of the document returned by the GetTileService request.  For the data source I'm trying to access the image is a 300x300 png containing 16 bit signed int values.  Deviating from this access pattern causes the jpl server to go through the much slower and less reliable wms access route.  The .earth file I posted seems to make the wms plugin only access the pre-cached tiles and I don't ever get refused connections.  Using the example jpl file in the osgEarth tests directory I can't ever seem to get much of anything from the server.

As for OSG version, I just compiled from the trunk last Friday, so it's pretty current.

Thanks,
Evan


On Tue, Aug 18, 2009 at 2:29 PM, jasonbeverage (via Nabble) <[hidden email]> wrote:
Hi Evan,

Try changing your tile_size to something like 32 or 64.  Setting it to 300 is making a 300x300 terrain tile which is a ton of geometry and could be causing issues with their server.  If that still doesn't fix the issue, try using tiff instead of png as the format, sometimes it works better with that server.  Also, keep in mind that that JPL server goes down constantly and refuses requests all the time, so it might not be the most reliable server to hit.

Also, what version of OSG are you using?

Thanks,

Jason

On Tue, Aug 18, 2009 at 3:39 PM, Evan Andersen (via Nabble) <[hidden email]> wrote:
I'm trying to access the NED 1 arc-second elevation data hosted on the NASA JPL OnEarth server using their tile scheme.  The source of the .earth file I'm using is included below.  I can download elevation tiles fine, but when I zoom in past the first couple of LOD's I start to see a lot of strange artifacts in the terrain.  If I look at the wireframe I can see parts of it that fold over the top or underneath other parts of the terrain.  Any ideas on what might be causing this?

Evan


<map name="JPL NED 1" type="geocentric">
 
  <heightfield name="Continental US Elevation" driver="wms">
    <url>http://onearth.jpl.nasa.gov/wms.cgi</url>
    <layers>us_ned</layers>
    <style>feet_short_int</style>
    <format>png</format>
    <tile_size>300</tile_size>
    <elevation_unit>ft</elevation_unit>
  </heightfield>

  <vertical_scale>8</vertical_scale>

  <skirt_ratio>0.01</skirt_ratio>
 
</map>





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Evan Andersen Evan Andersen
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Re: Problem creating heightfield from JPL OnEarth server

Thanks for looking into this Jason.  I hadn't tried changing the skirt ratio, but that makes the problem go away for me too.

I get the same out of memory problems with those huge tiles.  I'm thinking of writing a special driver that will return a profile with smaller tiles to osgEarth and then temporarily cache the big tiles that get downloaded and break them into smaller tiles to feed to osgEarth.

It would be great to be able to get terrain elevation from a better source, but this is the only one I know of that has 3 arc second and 1 arc second data.  I certainly appreciate your making the SRTM30 data set available, as it has been very useful, but when we are creating flight plans for our UAVs it is better to use higher-resolution data.  In the past I've manually downloaded elevation data from the USGS seamless site, but that site is painfully slow to use and I'd really like to have automated access to the elevation data.

Evan
jasonbeverage jasonbeverage
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Re: Problem creating heightfield from JPL OnEarth server

Hi Evan,

One of the better datasources for elevation data that I've played with is the CGIAR elevation dataset at http://srtm.csi.cgiar.org/.  It's 90m for the the whole world.  osgEarth can handle multiple elevation data sources, so you could use the SRTM 30 data as a base, then add insets from the CGIAR in areas that needed higher resolution data.  They have an FTP available for the tiles or you can search and download just the ones you need.

A driver like that would be a great addition to osgEarth and would definitely be welcome!

Thanks,

Jason

On Tue, Aug 18, 2009 at 6:07 PM, Evan Andersen (via Nabble) <[hidden email]> wrote:
Thanks for looking into this Jason.  I hadn't tried changing the skirt ratio, but that makes the problem go away for me too.

I get the same out of memory problems with those huge tiles.  I'm thinking of writing a special driver that will return a profile with smaller tiles to osgEarth and then temporarily cache the big tiles that get downloaded and break them into smaller tiles to feed to osgEarth.

It would be great to be able to get terrain elevation from a better source, but this is the only one I know of that has 3 arc second and 1 arc second data.  I certainly appreciate your making the SRTM30 data set available, as it has been very useful, but when we are creating flight plans for our UAVs it is better to use higher-resolution data.  In the past I've manually downloaded elevation data from the USGS seamless site, but that site is painfully slow to use and I'd really like to have automated access to the elevation data.

Evan


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Evan Andersen Evan Andersen
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Re: Problem creating heightfield from JPL OnEarth server

Thanks for the tip about the elevation source Jason.  I'll see if I can work some time to develop a driver into my schedule.

Evan