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List: flightgear-devel
Subject: Re: [Flightgear-devel] Sun below horizon
From: Tim Moore <timoore33 () gmail ! com>
Date: 2014-10-13 8:37:51
Message-ID: CAPK_1fw1hOWcrK22dm9vvbwd4G2nFCcBgbY5vcX2zPsnm4nq0Q () mail ! gmail ! com
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This seems like a reasonable approach, given the scenery-building process,
and the transition between the first two LODs should be relatively
seamless. In this approach I think you would want to bake the roads and
stuff into a texture for the whole tile for those LODs that don't include
the polygonal features.. At lower LODs there will be popping, but maybe
those will be off in the fog.
It's much harder, if not impossible, to do seamless LOD transitions with an
irregular triangle network than with a regular grid. However, we have a
hard requirement for perfect terrain borders on runways (which I
understand) and roads and other vector features (which I don't :-) )
Thorsten is referring to a suggestion of mine to represent the terrain as a
regular grid and "paint" the vector features into a texture generated at
runtime for the appropriate LOD.
Tim
On Mon, Oct 13, 2014 at 1:14 AM, Peter Sadrozinski <psadrozinski@gmail.com>
wrote:
> I am planning on supporting .spt files in a future terragear. Mathais had
> a demo at last year's fsweekend, but I just saw screenshots.
>
> The idea was to have the highest lod as is. the next with the same mesh,
> just no line features.
>
> Next level with reduced terrain mesh and landclass complexity. I've asked
> Martin if it was possible to get a 'reduced' corrine shapefile set. He's
> been busy with the raster to vector north american work.
>
> Eventually we get vmap0 and very rough terrain, then the sphere.
>
> Mathais has commited enough to get a rough demo. see here:
>
> http://wiki.flightgear.org/FGViewer
>
> I may be mistaken on some of these details.
>
> As for terragear, I've only started supporting the
> .spt directory structure in gdalchop for chopping the different tile sizes.
>
> Pete
> On Oct 12, 2014 9:42 AM, "Curtis Olson" <curtolson@flightgear.org> wrote:
>
>> When we talk about terrain LOD, one of the first topics to discuss is the
>> strategy to seamlessly join neighboring tiles of different LOD. As we
>> know, any discontinuity between triangles, even if it emerges due to
>> floating point rounding issues, causes really ugly aliasing seams between
>> those structures. There are a number of strategies that come to mind, all
>> with their own strengths and weaknesses. There is also a range of
>> continuous lod based approaches (i.e ROAM, etc.) that try to maintain a
>> consistent resolution in screen space. Continuous LOD algorithms also have
>> strengths and weaknesses.
>>
>> We did look at all this very carefully when FlightGear was first started
>> and our original scheme was first established. We tried to look past
>> popular trends, look ahead to future hardware, and we made the choice that
>> seemed best at the time. Then after making the choice we set out to make
>> it work as well as we could.
>>
>> That was a few years ago now. Hardware has certainly changed. Some of
>> the usage and priorities of FlightGear has changed in the meantime.
>> Perhaps it is a fine time to reevaluate the original design choices. But
>> any change will (or could) involve a ton of effort both on the FlightGear
>> rendering engine side of the equation, but also on the terragear side of
>> the equation, preparing and processing all the gis data sources and
>> generating all the complex scenery structures.
>>
>> Best regards,
>>
>> Curt.
>>
>> On Sun, Oct 12, 2014 at 4:42 AM, Renk Thorsten <thorsten.i.renk@jyu.fi>
>> wrote:
>>
>>> > I apologize. If anyone really wants to talk about terrain LOD, there
>>> is a
>>> > lot to say on the subject.
>>>
>>> I'd be interested in how you'd like to do it. My own idea would be to
>>> compute different LOD levels of the terrain mesh offline and store them on
>>> disk, loading in rings according to distance. I remember you talked at some
>>> point about just painting roads onto the terrain mesh, but I guess that
>>> will make the increasing number of motorcycle enthusiasts unhappy which
>>> rely on a road having a different material definition.
>>>
>>> I'm still not completely clear on how much of the vertex count in 2.0
>>> scenery is due to line features vs. elevation and landcover mesh density.
>>>
>>> * Thorsten
>>>
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>>>
>>
>>
>>
>> --
>> Curtis Olson:
>> http://www.atiak.com - http://www.flightgear.org -
>> http://gallinazo.flightgear.org
>>
>>
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>> https://lists.sourceforge.net/lists/listinfo/flightgear-devel
>>
>>
>
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>
[Attachment #5 (text/html)]
<div dir="ltr">This seems like a reasonable approach, given the scenery-building \
process, and the transition between the first two LODs should be relatively seamless. \
In this approach I think you would want to bake the roads and stuff into a texture \
for the whole tile for those LODs that don't include the polygonal features.. At \
lower LODs there will be popping, but maybe those will be off in the \
fog.<div><br></div><div>It's much harder, if not impossible, to do seamless LOD \
transitions with an irregular triangle network than with a regular grid. However, we \
have a hard requirement for perfect terrain borders on runways (which I understand) \
and roads and other vector features (which I don't :-) ) Thorsten is referring to \
a suggestion of mine to represent the terrain as a regular grid and "paint" \
the vector features into a texture generated at runtime for the appropriate \
LOD.<br><div class="gmail_extra"><br></div><div class="gmail_extra">Tim<br><div \
class="gmail_quote">On Mon, Oct 13, 2014 at 1:14 AM, Peter Sadrozinski <span \
dir="ltr"><<a href="mailto:psadrozinski@gmail.com" \
target="_blank">psadrozinski@gmail.com</a>></span> wrote:<br><blockquote \
class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc \
solid;padding-left:1ex"><p>I am planning on supporting .spt files in a future \
terragear. Mathais had a demo at last year's fsweekend, but I just saw \
screenshots.</p> <p>The idea was to have the highest lod as is. the next with the \
same mesh, just no line features.</p> <p>Next level with reduced terrain mesh and \
landclass complexity. I've asked Martin if it was possible to get a \
'reduced' corrine shapefile set. He's been busy with the raster to \
vector north american work.</p> <p>Eventually we get vmap0 and very rough terrain, \
then the sphere.</p> <p>Mathais has commited enough to get a rough demo. see \
here:</p> <p><a href="http://wiki.flightgear.org/FGViewer" \
target="_blank">http://wiki.flightgear.org/FGViewer</a></p> <p>I may be mistaken on \
some of these details.</p> <p>As for terragear, I've only started supporting the \
<br>
.spt directory structure in gdalchop for chopping the different tile sizes.</p>
<p>Pete<br>
</p><div class="HOEnZb"><div class="h5">
<div class="gmail_quote">On Oct 12, 2014 9:42 AM, "Curtis Olson" <<a \
href="mailto:curtolson@flightgear.org" \
target="_blank">curtolson@flightgear.org</a>> wrote:<br \
type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 \
.8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">When we talk about \
terrain LOD, one of the first topics to discuss is the strategy to seamlessly join \
neighboring tiles of different LOD. As we know, any discontinuity between \
triangles, even if it emerges due to floating point rounding issues, causes really \
ugly aliasing seams between those structures. There are a number of strategies that \
come to mind, all with their own strengths and weaknesses. There is also a range of \
continuous lod based approaches (i.e ROAM, etc.) that try to maintain a consistent \
resolution in screen space. Continuous LOD algorithms also have strengths and \
weaknesses.<div><br>We did look at all this very carefully when FlightGear was first \
started and our original scheme was first established. We tried to look past \
popular trends, look ahead to future hardware, and we made the choice that seemed \
best at the time. Then after making the choice we set out to make it work as well \
as we could.</div><div><br></div><div>That was a few years ago now. Hardware has \
certainly changed. Some of the usage and priorities of FlightGear has changed in \
the meantime. Perhaps it is a fine time to reevaluate the original design choices. \
But any change will (or could) involve a ton of effort both on the FlightGear \
rendering engine side of the equation, but also on the terragear side of the \
equation, preparing and processing all the gis data sources and generating all the \
complex scenery structures.</div><div><br></div><div>Best \
regards,</div><div><br>Curt.</div></div><div class="gmail_extra"><br><div \
class="gmail_quote">On Sun, Oct 12, 2014 at 4:42 AM, Renk Thorsten <span \
dir="ltr"><<a href="mailto:thorsten.i.renk@jyu.fi" \
target="_blank">thorsten.i.renk@jyu.fi</a>></span> wrote:<br><blockquote \
class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc \
solid;padding-left:1ex"><span>> I apologize. If anyone really wants to talk about \
terrain LOD, there is a<br> > lot to say on the subject.<br>
<br>
</span>I'd be interested in how you'd like to do it. My own idea would be to \
compute different LOD levels of the terrain mesh offline and store them on disk, \
loading in rings according to distance. I remember you talked at some point about \
just painting roads onto the terrain mesh, but I guess that will make the increasing \
number of motorcycle enthusiasts unhappy which rely on a road having a different \
material definition.<br> <br>
I'm still not completely clear on how much of the vertex count in 2.0 scenery is \
due to line features vs. elevation and landcover mesh density.<br> <br>
* Thorsten<br>
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target="_blank">http://p.sf.net/sfu/Zoho</a><br> \
<div><div>_______________________________________________<br> Flightgear-devel \
mailing list<br> <a href="mailto:Flightgear-devel@lists.sourceforge.net" \
target="_blank">Flightgear-devel@lists.sourceforge.net</a><br> <a \
href="https://lists.sourceforge.net/lists/listinfo/flightgear-devel" \
target="_blank">https://lists.sourceforge.net/lists/listinfo/flightgear-devel</a><br> \
</div></div></blockquote></div><br><br clear="all"><div><br></div>-- <br><div \
dir="ltr"><div>Curtis Olson:</div><div><a href="http://www.atiak.com/" \
target="_blank">http://www.atiak.com</a> - <a href="http://www.flightgear.org/" \
target="_blank">http://www.flightgear.org</a> - <a \
href="http://gallinazo.flightgear.org/" \
target="_blank">http://gallinazo.flightgear.org</a></div></div> </div>
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target="_blank">http://p.sf.net/sfu/Zoho</a><br>_______________________________________________<br>
Flightgear-devel mailing list<br>
<a href="mailto:Flightgear-devel@lists.sourceforge.net" \
target="_blank">Flightgear-devel@lists.sourceforge.net</a><br> <a \
href="https://lists.sourceforge.net/lists/listinfo/flightgear-devel" \
target="_blank">https://lists.sourceforge.net/lists/listinfo/flightgear-devel</a><br> \
<br></blockquote></div> \
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<a href="mailto:Flightgear-devel@lists.sourceforge.net">Flightgear-devel@lists.sourceforge.net</a><br>
<a href="https://lists.sourceforge.net/lists/listinfo/flightgear-devel" \
target="_blank">https://lists.sourceforge.net/lists/listinfo/flightgear-devel</a><br> \
<br></blockquote></div><br></div></div></div>
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