Re: [Flightgear-devel] Tides in FlightGear?

[Oliver]

Am Freitag, den 26.05.2006, 11:03 -0500 schrieb Curtis L. Olson:
> Martin Doege wrote:
> 
> > However, calculating the tide for a given coordinate is probably the 
> > lesser problem here (one can use xtide's output for reference, etc.) 
> > My main issue  is whether the visualization of the tidal effects can 
> > somehow be done with e.g. a Nasal script (good) or by extensively 
> > modifying the FG engine itself (not so good, since the FG/SimGear 
> > source code is pretty abstract and not very well-commented IMHO)
> 
> 
> You would almost have to redo the scenery in the areas with ocean 
> coverage to include the ocean floor elevation, then draw the ocean as a 
> seperate layer that can be moved up and down exposing more or less of 
> the terrain.
> 
> The trick maybe to find a good sea floor elevation database that is 
> reasonably compatible with SRTM, and mesh the two data sets seamlessly.
> 
> Curt

What about using fake sea floor elevation data for the beginning
when there is no real data available? 
Approaching it this way it should be possible to allready start with the
implementation of the code and technical side of view.
Real sea floor elevation data could then be integrated later, when we
have found some good free sea elevation data.

Best Regards,
 Oliver C.

 



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Re: [Flightgear-devel] Tides in FlightGear?

[Oliver]

Am Sonntag, den 28.05.2006, 14:42 +0200 schrieb Martin Doege:
> And since one of the major selling points of "Flight Simulator X" will
> be, at least according to the screenshots and trailers, the more
> realistic depiction of water in all its pixel shader-rendered glory,
> it would be great if the water in FG would also be a little more than
> just the big blue parking lot it is right now. :-)

Maybe we could integrate code from the submarine simulation "Danger of
the Deep". They have allready very nice eye candy water effects.

Screenshots:
http://dangerdeep.sourceforge.net/gallery.php
http://dangerdeep.sourceforge.net/gallery/screenshot_0_1_1_01.jpg
http://dangerdeep.sourceforge.net/gallery/screenshot_0_1_1_02.jpg
http://dangerdeep.sourceforge.net/gallery/screenshot_0_1_1_03.jpg
http://dangerdeep.sourceforge.net/gallery/screenshot_0_1_1_04.jpg

It is an open source simulation like FlightGear and under the GPL
license, so there shouldn't be a problem with code reuse from a license
point of view. 

If we think about this a little further perhaps they might be interested
in a merge of both projects. Because even a submarine simulation needs
airplanes in the air and nice coast lines with hills and buildings on
the land that is visible from the sea. :)


Best Regards,
 Oliver C.





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Re: [Flightgear-devel] Tides in FlightGear?

[Josh Babcock]

Curtis L. Olson wrote:
> Martin Doege wrote:
> 
>> However, calculating the tide for a given coordinate is probably the
>> lesser problem here (one can use xtide's output for reference, etc.)
>> My main issue  is whether the visualization of the tidal effects can
>> somehow be done with e.g. a Nasal script (good) or by extensively
>> modifying the FG engine itself (not so good, since the FG/SimGear
>> source code is pretty abstract and not very well-commented IMHO)
> 
> 
> 
> You would almost have to redo the scenery in the areas with ocean
> coverage to include the ocean floor elevation, then draw the ocean as a
> seperate layer that can be moved up and down exposing more or less of
> the terrain.
> 
> The trick maybe to find a good sea floor elevation database that is
> reasonably compatible with SRTM, and mesh the two data sets seamlessly.
> 
> Curt.
> 

This would have a nice side effect of autmatically creating beaches.

Josh


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Re: [Flightgear-devel] Tides in FlightGear?

[Martin Doege]

Well, I'd be careful with such assumptions. You're correct in thatFreeBSD-6.0 is not recommended for heavy-load production use (say FTP
service with 3k simultaneous connections, I don't know if'ftp.cdrom.com' still exists).Still you can assume that it eaily handles 1 GByte of RAM and more. Mybet is that the port of Inkscape to FreeBSD probably "doesn't match the
operating system close enough". My experience is that you often have todeal with Linuxisms in OpenSource software which probably show obscurebehaviour on Unixes.
I just checked out the shell process limits and was shocked to find out
datasize was limited to 1 GB. I vaguely recall I already had to up it
from 512 MB to run FlightGear on FreeBSD a few months back.

So I just increased the values in /boot/loader.conf even further:

kern.maxdsiz="2048M"
kern.dfldsiz="2048M"
kern.maxssiz="256M"


and, lo and behold, after a reboot the process limit is now at 2
GB and Inkscape can load the SVG, consuming a rather whopping 1266 MB
of memory for a 12.9 MB image!

Unfortunately, because Inkscape is swapping all the time, editing the
SVG is still almost an impossibility, but at least in principle it
works now.

So I stand corrected: FreeBSD is a great operating system, it just has  some pretty stupid defaults for people who want to use big data sets. :-)

Martin

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Re: [Flightgear-devel] Tides in FlightGear?

[Martin Doege]

On 6/4/06, Martin Spott <[EMAIL PROTECTED]> wrote:
Still you can assume that it eaily handles 1 GByte of RAM and more. Mybet is that the port of Inkscape to FreeBSD probably "doesn't match theoperating system close enough". My experience is that you often have to
deal with Linuxisms in OpenSource software which probably show obscurebehaviour on Unixes. I think Inkscape does its allocating via the C++ standard library function like any other application. So I see no reason to think that hidden Linuxisms are the underlying problem here.
It looks like a FreeBSD issue to me because the failure occurs just as the physical memory is exhausted and the system starts to swap. And I believe the idea behind virtual memory is that the application does not have to know whether a page is in physical memory or swapped out. So the problem more than likely comes from the part of the system that "knows" what is happening, 
i.e. the virtual memory manager.But you are right, before filing a bug report, more tests with other memory-hungry apps would have to be conducted. And maybe this issue, if it exists in FreeBSD 6.0, is fixed in 6.1
. However, I don't want to upgrade right now, as the system works well enough in all other regards.Martin D.
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Re: [Flightgear-devel] Tides in FlightGear?

[Martin Spott]

"Martin Doege" wrote:

> So apparently Inkscape (or its developers) are not to blame here, it is the
> FreeBSD 6.0 virtual memory subsystem that seems to be a little wonky to say
> the least.

Well, I'd be careful with such assumptions. You're correct in that
FreeBSD-6.0 is not recommended for heavy-load production use (say FTP
service with 3k simultaneous connections, I don't know if
'ftp.cdrom.com' still exists).
Still you can assume that it eaily handles 1 GByte of RAM and more. My
bet is that the port of Inkscape to FreeBSD probably "doesn't match the
operating system close enough". My experience is that you often have to
deal with Linuxisms in OpenSource software which probably show obscure
behaviour on Unixes.

Cheers,
Martin.
-- 
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Re: [Flightgear-devel] Tides in FlightGear?

[Martin Doege]

On 6/3/06, Martin Doege <[EMAIL PROTECTED]> wrote:
Inkscape does not even seem to touch the existing 2 GB of swap, so adding more will help little. Memory usage just balloons to 750-800 MB, which is the physical memory minus memory used by KDE, X, etc., and then the app fails to allocate more.
I just tried to open the file in Inkscape 0.43 under Mac OS Xand it worked!Of course the poor little iBook is probably a little too slow to do much with the data after it has loaded, but at least the loading itself works nicely, even if it takes forever. I should try this on the other Mac tomorrow.
So apparently Inkscape (or its developers) are not to blame here, it is the FreeBSD 6.0 virtual memory subsystem that seems to be a little wonky to say the least.I should have considered this possibility earlier, but apparently sometimes FreeBSD users are a little full of themselves and consider "production releases" of their OS of choice unsinkable. Which may have been true in the 
4.x days, but not anymore, that much is certain! ;-)Martin D.
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Re: [Flightgear-devel] Tides in FlightGear?

[Martin Doege]

On 6/3/06, Anders Gidenstam <[EMAIL PROTECTED]> wrote:
If you have some spare disk space you could add more swap. I think thatcan be done using a swap-file so you don't even have to create anotherswap partition. See the man page for swapon(8) for more info.
Inkscape does not even seem to touch the existing 2 GB of swap, so adding more will help little. Memory usage just balloons to 750-800 MB, which is the physical memory minus memory used by KDE, X, etc., and then the app fails to allocate more.
I always thought virtual memory was somehow transparent to applications, but in this case there seems to be a marked distinction between physical memory and swap space for some reason.Martin D.

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Re: [Flightgear-devel] Tides in FlightGear?

[Chris Metzler]

On Sat, 3 Jun 2006 20:05:14 +0200
Martin Doege wrote:
>
> Maybe I should try to throw out more elements, based on their color? Or
> simply buy more RAM? :-)

Or file a bug.  It sounds like you have plenty of RAM, so I wouldn't
think this would be acceptable to the Inkscape folks.

-c

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Re: [Flightgear-devel] Tides in FlightGear?

[Anders Gidenstam]

On Sat, 3 Jun 2006, Martin Doege wrote:

> It looks like Inkscape needs to fit the whole image data into physical
> memory. It loads a little more of the file if I log into X without KDE, just
> some xterms, but it still crashes with a std::bad_alloc message when it has
> processed about 80%.

[snip]

> Maybe I should try to throw out more elements, based on their color? Or
> simply buy more RAM? :-)

If you have some spare disk space you could add more swap. I think that 
can be done using a swap-file so you don't even have to create another 
swap partition. See the man page for swapon(8) for more info.

Cheers,

Anders
-- 
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Email: anders(at)gidenstam.org
WWW: http://www.gidenstam.org/FlightGear/JSBSim-LTA/


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Re: [Flightgear-devel] Tides in FlightGear?

[Martin Doege]

On 6/3/06, Chris Metzler <[EMAIL PROTECTED]> wrote:

Is the crash really related to size?  Maybe the SVG conversion wasbugged?  (of course, Inkscape should react to that better than
by crashing, as well, but anyway.)
It looks like Inkscape needs to fit the whole image data into physical
memory. It loads a little more of the file if I log into X without KDE,
just some xterms, but it still crashes with a std::bad_alloc message
when it has processed about 80%.

I have slimmed down the SVG somewhat by removing the font definitions,
bitmap images, text, and the red hatching with a text editor and grep.
While the file is now "only" 13.5 MB in size, Inkscape still cannot
load the whole thing.

Maybe I should try to throw out more elements, based on their color? Or simply buy more RAM? :-)

Martin D.



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Re: [Flightgear-devel] Tides in FlightGear?

[Arnt Karlsen]

On Sat, 3 Jun 2006 16:59:45 + (UTC), Martin wrote in message 
<[EMAIL PROTECTED]>:

> Arnt Karlsen wrote:
> 
> > ..Martin, see if you can find such data around GVAC (Cape Verde), 
> > looks like I have TerrorGear working in a few hours.
> 
> If you point me to a location where I can fetch such data I'll tell
> you if I managed to find it  ;-)

..pass, got a dead disk to try pry out TerrorGear from.  
Seriously, no big deal, just a few more hours.  ;o)

-- 
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...with a number of polar bear hunters in his ancestry...
  Scenarios always come in sets of three: 
  best case, worst case, and just in case.



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Re: [Flightgear-devel] Tides in FlightGear?

[Martin Spott]

Arnt Karlsen wrote:

> ..Martin, see if you can find such data around GVAC (Cape Verde), 
> looks like I have TerrorGear working in a few hours.

If you point me to a location where I can fetch such data I'll tell
you if I managed to find it  ;-)

Martin.
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Re: [Flightgear-devel] Tides in FlightGear?

[Arnt Karlsen]

On Sat, 3 Jun 2006 12:57:05 + (UTC), Martin wrote in message 
<[EMAIL PROTECTED]>:

> "Martin Doege" wrote:
> 
> > I have looked around for high-resolution Wadden Sea bathymetry on
> > the Web and the best I have found yet is this
> > map > P-CWSS-2003.pdf>
> > http://www.waddensea-secretariat.org/news/documents/WSP-Maps/MAP-CWSS-2003.pdf
> [...]
> > The problem is of course extracting the data back onto a grid to
> > interpolate it.
> 
> Wow !! the "Disclaimer" doesn't prevent us from using this document
> together with FlightGear or the Landcover-DB. We definitely should try
> to get this vector data into GRASS or some comparable system and
> separate the different layers - in case of doubt we even could use
> commercial software to do the required conversion. Once someone is
> able to load the data into GRASS, the geo-referencing should not pose
> any serious problem as lots of significant points have a well-known
> location. I'm looking forward to get hold of this data as I'm
> personally _very_ interested in this area 

..Martin, see if you can find such data around GVAC (Cape Verde), 
looks like I have TerrorGear working in a few hours.
Thanks to Fred B. for sending me a working gpc Makefile.  :o)

-- 
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...with a number of polar bear hunters in his ancestry...
  Scenarios always come in sets of three: 
  best case, worst case, and just in case.




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Re: [Flightgear-devel] Tides in FlightGear?

[Martin Spott]

"Martin Doege" wrote:

> I have looked around for high-resolution Wadden Sea bathymetry on the Web
> and the best I have found yet is this
> map
> http://www.waddensea-secretariat.org/news/documents/WSP-Maps/MAP-CWSS-2003.pdf
[...]
> The problem is of course extracting the data back onto a grid to interpolate
> it.

Wow !! the "Disclaimer" doesn't prevent us from using this document
together with FlightGear or the Landcover-DB. We definitely should try
to get this vector data into GRASS or some comparable system and
separate the different layers - in case of doubt we even could use
commercial software to do the required conversion. Once someone is able
to load the data into GRASS, the geo-referencing should not pose any
serious problem as lots of significant points have a well-known
location. I'm looking forward to get hold of this data as I'm
personally _very_ interested in this area 

Cheers,
Martin.
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Re: [Flightgear-devel] Tides in FlightGear?

[Chris Metzler]

On Sat, 3 Jun 2006 00:45:33 -0400
Ampere K. Hardraade wrote:
>On Friday 02 June 2006 23:14, Chris Metzler wrote:
>> Is the crash really related to size?  Maybe the SVG conversion was
>> bugged?  (of course, Inkscape should react to that better than
>> by crashing, as well, but anyway.)
> 
> If you have ever tried to convert complex PDF files into SVG format,
> then you would know that the resulting SVG file is very verbose. ;-)

Oh, I have no doubt.  But I'm all about filing bug reports when
appropriate, and wanted to encourage doing so if that was the source
of Inkscape's problem.

-c

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Re: [Flightgear-devel] Tides in FlightGear?

[Ampere K. Hardraade]

On Friday 02 June 2006 23:14, Chris Metzler wrote:
> Is the crash really related to size?  Maybe the SVG conversion was
> bugged?  (of course, Inkscape should react to that better than
> by crashing, as well, but anyway.)
>
> -c

If you have ever tried to convert complex PDF files into SVG format, then you 
would know that the resulting SVG file is very verbose. ;-)

Ampere


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Re: [Flightgear-devel] Tides in FlightGear?

[Chris Metzler]

On Fri, 2 Jun 2006 17:46:42 +0200
Martin Doege wrote:
> 
> The conversion worked, but the resulting 17 MB SVG file crashes Inkscape
> 0.42 on import despite the 1 GB of RAM. How crappy!

Is the crash really related to size?  Maybe the SVG conversion was
bugged?  (of course, Inkscape should react to that better than
by crashing, as well, but anyway.)

-c

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Re: [Flightgear-devel] Tides in FlightGear?

[Martin Doege]

Basically, you could model a "tidal area" as a triangle mesh (asdetailed as you like) where the triangle type is "tidal" and each
triangle also carries a parameter "X" which is the local tide-height atwhich that triangle is covered by water. A tide-calculator finds localtide-height in a slow-running background loop, and every iteration of
that loop, all triangles where X < tide-height are textured as "water",otherwise as "sand" (or mud).What's nice about that approach is that you can model tidal reaches withwhatever detail you want. It could just be "tide in"/"tide out" as
suggested by Curt (above) or vastly complex, handling the water flows ofmudflats like the "wadden" area or Mont St. Michel.
I have looked around for high-resolution Wadden Sea bathymetry on the Web and the best I have found yet is 

this map
http://www.waddensea-secretariat.org/news/documents/WSP-Maps/MAP-CWSS-2003.pdf

(CAUTION: huge PDF, low-res version here:
http://www.waddensea-secretariat.org/news/documents/WSP-Maps/MAP-CWSS.jpg
).

The problem is of course extracting the data back onto a grid to
interpolate it. I suppose if I had Adobe Illustrator, I could simply import
the PDF, delete everything that does not belong to the depth lines and
export the image. Unfortunately, Inkscape cannot import PDFs as it
seems. So I will try to convert this to SVG, maybe I can import it then.
I have also sent an email to the Wadden Sea Secretariat asking if they can provide the gridded or raw data in a better format,
but generally scientific raw data is a lot harder to come by in Europe
than in the US, so my expectations are not very high.

Martin


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Re: [Flightgear-devel] Tides in FlightGear?

[Martin Doege]

 So I will try to convert this to SVG, maybe I can import it then.

The conversion worked, but the resulting 17 MB SVG file crashes Inkscape 0.42 on import despite the 1 GB of RAM. How crappy!

Martin D.



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Re: [Flightgear-devel] Tides in FlightGear?

[Erik Hofman]

>> Curtis L. Olson wrote:
>>
>>> Martin Spott wrote:
>>>
 The triangles don't have to be changed at all because in our Scenery
 the tidal area is part of the ocean. The idea was about changing
 nothing but the colour,
>>>
>>> Ok, so you are only talking about areas that are marked explicitly as 
>>> tidal areas in our land use/land cover data base, and then they would 
>>> be either at full tide or no tide ... that's probably simpler to manage.

Actually there is another method that caught my attention lately; 3d 
textures. By using a two layer 3d texture one could seamlessly blend 
between the layers based on a parameter that influences the texture 
z-parameter.

Erik

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Re: [Flightgear-devel] Tides in FlightGear?

[Steve Hosgood]

Durk Talsma wrote:

> Curtis L. Olson wrote:
>
>> Martin Spott wrote:
>>
>>> The triangles don't have to be changed at all because in our Scenery
>>> the tidal area is part of the ocean. The idea was about changing
>>> nothing but the colour,
>>>   
>>
>>
>> Ok, so you are only talking about areas that are marked explicitly as 
>> tidal areas in our land use/land cover data base, and then they would 
>> be either at full tide or no tide ... that's probably simpler to manage.
>>
>> Curt.
>>
> I like the idea. Having some real-life experience flying over the 
> "wadden" area that Martin (Doege) referred to, I can tell that the low 
> tide areas can be very scenic. A change in texture would indeed 
> suffice, because the elevation differences are almost negligable.


Basically, you could model a "tidal area" as a triangle mesh (as 
detailed as you like) where the triangle type is "tidal" and each 
triangle also carries a parameter "X" which is the local tide-height at 
which that triangle is covered by water. A tide-calculator finds local 
tide-height in a slow-running background loop, and every iteration of 
that loop, all triangles where X < tide-height are textured as "water", 
otherwise as "sand" (or mud).

What's nice about that approach is that you can model tidal reaches with 
whatever detail you want. It could just be "tide in"/"tide out" as 
suggested by Curt (above) or vastly complex, handling the water flows of 
mudflats like the "wadden" area or Mont St. Michel.

I've been interested in tides for years, and although 'Xtide' has now 
appeared (which outdoes my efforts), I've been offering a tide 
calculator program on my website for years: see 
http://tallyho.bc.nu/~steve/tides.html

The underlying maths is very much simplified compared with Xtide, but 
would be fine for Flightgear. Help yourselves if you want it!
Steve.



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Re: [Flightgear-devel] Tides in FlightGear?

[Martin Doege]

I like this idea, as it is a more generic approach and could work for steeper
shorelines (like those around KSFO).  Smaller layers could then be used to
simulate the effects of waves as well, and based on the camera's distance to
these layers, we could then play the sounds for wave.

Water surface should be handled differently than land right from the
beginning.  Right now, any plane could land on the water as if the water is a
giant runway.  By having the water as a separated mesh, we could finally
simulate the plane-water interaction properly.  I feel that this method would
move us into the right direction.


And since one of the major selling points of "Flight Simulator X" will
be, at least according to the screenshots and trailers, the more
realistic depiction of water in all its pixel shader-rendered glory,
it would be great if the water in FG would also be a little more than
just the big blue parking lot it is right now. :-)

Martin D.


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Re: [Flightgear-devel] Tides in FlightGear?

[Detlef Faber]

Am Samstag, den 27.05.2006, 16:14 -0400 schrieb Ampere K. Hardraade:
> On Friday 26 May 2006 12:03, Curtis L. Olson wrote:
> > You would almost have to redo the scenery in the areas with ocean
> > coverage to include the ocean floor elevation, then draw the ocean as a
> > seperate layer that can be moved up and down exposing more or less of
> > the terrain.
> >
> > The trick maybe to find a good sea floor elevation database that is
> > reasonably compatible with SRTM, and mesh the two data sets seamlessly.
> >
> > Curt.
> 
> I like this idea, as it is a more generic approach and could work for steeper 
> shorelines (like those around KSFO).  Smaller layers could then be used to 
> simulate the effects of waves as well, and based on the camera's distance to 
> these layers, we could then play the sounds for wave.
> 
> Water surface should be handled differently than land right from the 
> beginning.  Right now, any plane could land on the water as if the water is a 
> giant runway.  By having the water as a separated mesh, we could finally 
> simulate the plane-water interaction properly.  I feel that this method would 
> move us into the right direction.
> 
> Ampere
> 
that would be a chance for completing my albatros seaplane, imagine
flying around those caribbean islands ... 


Greetings

Detlef

http://www.sol2500.net/flightgear


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Re: [Flightgear-devel] Tides in FlightGear?

[Ampere K. Hardraade]

On Friday 26 May 2006 12:03, Curtis L. Olson wrote:
> You would almost have to redo the scenery in the areas with ocean
> coverage to include the ocean floor elevation, then draw the ocean as a
> seperate layer that can be moved up and down exposing more or less of
> the terrain.
>
> The trick maybe to find a good sea floor elevation database that is
> reasonably compatible with SRTM, and mesh the two data sets seamlessly.
>
> Curt.

I like this idea, as it is a more generic approach and could work for steeper 
shorelines (like those around KSFO).  Smaller layers could then be used to 
simulate the effects of waves as well, and based on the camera's distance to 
these layers, we could then play the sounds for wave.

Water surface should be handled differently than land right from the 
beginning.  Right now, any plane could land on the water as if the water is a 
giant runway.  By having the water as a separated mesh, we could finally 
simulate the plane-water interaction properly.  I feel that this method would 
move us into the right direction.

Ampere


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Re: [Flightgear-devel] Tides in FlightGear?

[Arnt Karlsen]

On Fri, 26 May 2006 20:16:14 + (UTC), Martin wrote in message 
<[EMAIL PROTECTED]>:

> "Martin Doege" wrote:
> 
> > If the low tide pattern is already marked in the land cover database
> > as such, [...]
> 
> No, we currently don't have the low tide marks stored in the DB but
> I'm sure that we could retrieve it somewhere. For almost every area
> that features such a significant tidal phenomenon there's always some
> website which carries some photos or charts that we're allowed to use
> for digitizing.
> This task won't be done done in five minutes, some 'real' work is
> required, but it should not be _that_ difficult because we don't have
> to invent something totally new.

..you're thinking xtide and nautical maps?  Only the latter would be
needed for the tidal scenery builds, and xtide could be drawn into
non-posix code builds like brlcad(.org) adds jove to have an 
emacs-like command editor.

-- 
..med vennlig hilsen = with Kind Regards from Arnt... ;o)
...with a number of polar bear hunters in his ancestry...
  Scenarios always come in sets of three: 
  best case, worst case, and just in case.




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Re: [Flightgear-devel] Tides in FlightGear?

[Martin Spott]

"Martin Doege" wrote:

> If the low tide pattern is already marked in the land cover database
> as such, [...]

No, we currently don't have the low tide marks stored in the DB but I'm
sure that we could retrieve it somewhere. For almost every area that
features such a significant tidal phenomenon there's always some
website which carries some photos or charts that we're allowed to use
for digitizing.
This task won't be done done in five minutes, some 'real' work is
required, but it should not be _that_ difficult because we don't have
to invent something totally new.

Cheers,
Martin.
-- 
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--


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Re: [Flightgear-devel] Tides in FlightGear?

[Martin Doege]

Ok, so you are only talking about areas that are marked explicitly as
tidal areas in our land use/land cover data base, and then they would be
either at full tide or no tide ... that's probably simpler to manage.


The idea was more like a linear transition between the high and low
tide patterns. Only having the scenery flip-flop between two states is
probably better than nothing at all but not perfect either (e.g.,
around Mont Saint Michel, the rising water has a horizonal speed of up
to 1 m/s, so you can watch its movement easily!).

If the low tide pattern is already marked in the land cover database
as such, the only problem is calculating the horizontal shapes of the
water as it rises (or falls). If the bathymetry is unknown, perhaps
the horizontal patterns can be faked by using a 2D cellular automaton.
The rules just have to set up so that the water rushes back into the
narrower areas (where the water is supposedly deeper) first and when
it falls, retreats from those areas last. The CA could be running in
FG and occasionally update the sea / mud status of a randomly selected
tile that is both close to the water and within the visible range.

Martin


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Re: [Flightgear-devel] Tides in FlightGear?

[Durk Talsma]

Curtis L. Olson wrote:

Martin Spott wrote:

The triangles don't have to be changed at all because in our Scenery
the tidal area is part of the ocean. The idea was about changing
nothing but the colour,
  


Ok, so you are only talking about areas that are marked explicitly as 
tidal areas in our land use/land cover data base, and then they would 
be either at full tide or no tide ... that's probably simpler to manage.


Curt.

I like the idea. Having some real-life experience flying over the 
"wadden" area that Martin (Doege) referred to, I can tell that the low 
tide areas can be very scenic. A change in texture would indeed suffice, 
because the elevation differences are almost negligable.


Cheers,
Durk


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Re: [Flightgear-devel] Tides in FlightGear?

[Curtis L. Olson]

Martin Spott wrote:

The triangles don't have to be changed at all because in our Scenery
the tidal area is part of the ocean. The idea was about changing
nothing but the colour,
  


Ok, so you are only talking about areas that are marked explicitly as 
tidal areas in our land use/land cover data base, and then they would be 
either at full tide or no tide ... that's probably simpler to manage.


Curt.


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Re: [Flightgear-devel] Tides in FlightGear?

[Martin Spott]

"Curtis L. Olson" wrote:

>  From a technical standpoint, how would you plan to "move" shoreline and 
> change all the underlying triangle structures in real time?

The triangles don't have to be changed at all because in our Scenery
the tidal area is part of the ocean. The idea was about changing
nothing but the colour,

Martin.
-- 
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Re: [Flightgear-devel] Tides in FlightGear?

[Curtis L. Olson]

Martin Spott wrote:


"Curtis L. Olson" wrote:

 

The trick maybe to find a good sea floor elevation database that is 
reasonably compatible with SRTM, and mesh the two data sets seamlessly.
   



 http://www.ngdc.noaa.gov/mgg/bathymetry/relief.html

has an interesting survey on bathymetric data. But I don't think we
need a realistic simulation of the effect for use in Flightgear,
changing colours according to the tidal changes should be sufficient.
This could be done by declaring respective areas of the ocean as
tideland and moving the shoreline proportionally to the time that has
passed since the last hig- or low-tides.
Still someone would have to develop a schema to calculate the tides 
 



From a technical standpoint, how would you plan to "move" shoreline and 
change all the underlying triangle structures in real time?


Curt.

--
Curtis Olsonhttp://www.flightgear.org/~curt
HumanFIRST Program  http://www.humanfirst.umn.edu/
FlightGear Project  http://www.flightgear.org
Unique text:2f585eeea02e2c79d7b1d8c4963bae2d



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Re: [Flightgear-devel] Tides in FlightGear?

[Martin Spott]

"Curtis L. Olson" wrote:

> The trick maybe to find a good sea floor elevation database that is 
> reasonably compatible with SRTM, and mesh the two data sets seamlessly.

  http://www.ngdc.noaa.gov/mgg/bathymetry/relief.html

has an interesting survey on bathymetric data. But I don't think we
need a realistic simulation of the effect for use in Flightgear,
changing colours according to the tidal changes should be sufficient.
This could be done by declaring respective areas of the ocean as
tideland and moving the shoreline proportionally to the time that has
passed since the last hig- or low-tides.
Still someone would have to develop a schema to calculate the tides 

Martin.
-- 
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Re: [Flightgear-devel] Tides in FlightGear?

[Curtis L. Olson]

Martin Doege wrote:

However, calculating the tide for a given coordinate is probably the 
lesser problem here (one can use xtide's output for reference, etc.) 
My main issue  is whether the visualization of the tidal effects can 
somehow be done with e.g. a Nasal script (good) or by extensively 
modifying the FG engine itself (not so good, since the FG/SimGear 
source code is pretty abstract and not very well-commented IMHO)



You would almost have to redo the scenery in the areas with ocean 
coverage to include the ocean floor elevation, then draw the ocean as a 
seperate layer that can be moved up and down exposing more or less of 
the terrain.


The trick maybe to find a good sea floor elevation database that is 
reasonably compatible with SRTM, and mesh the two data sets seamlessly.


Curt.

--
Curtis Olsonhttp://www.flightgear.org/~curt
HumanFIRST Program  http://www.humanfirst.umn.edu/
FlightGear Project  http://www.flightgear.org
Unique text:2f585eeea02e2c79d7b1d8c4963bae2d



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Re: [Flightgear-devel] Tides in FlightGear?

[Martin Doege]

It would have to be slightly more than just that. At the very least,
you'd need a delay-factor for the local hour-angle of the moon. Also anamplitude-factor.Even then, you'd sometimes get the tide happening about an hourdisplaced from reality due to the loss of the solar tide. If you added a
simple solar tide (i.e a delay factor for the local solar hour-angle anda solar-tide amplitude-factor) then you'd probably be getting a prettygood rough approximation for a given area. Good enough for a flight-sim,
certainly.
Yes, some kind of tide delay factor, preferably one that can vary from
place to place, as well as solar and lunar tidal amplitudes (from hour
angle and distance) would probably be required to get something roughly
accurate.

However, calculating the tide
for a given coordinate is probably the lesser problem here (one can use
xtide's output for reference, etc.) My main issue  is whether the
visualization of the tidal effects can somehow be done with e.g. a
Nasal script (good) or by extensively modifying the FG engine itself
(not so good, since the FG/SimGear source code is pretty abstract and
not very well-commented IMHO)

It would also better model those areas of the world where the solar tidedominates

I thought the lunar tide is always dominant and the solar tide just
adds to it during spring tide. Or have I misunderstood you there?

Martin

Re: [Flightgear-devel] Tides in FlightGear?

[Steve Hosgood]

Martin Doege wrote:

Of course the tide calculations would not be required to be extremely 
accurate à la xtide -- the hour angle of the Moon would probably be 
quite sufficient as a broad indication of tide.




It would have to be slightly more than just that. At the very least, 
you'd need a delay-factor for the local hour-angle of the moon. Also an 
amplitude-factor.


Even then, you'd sometimes get the tide happening about an hour 
displaced from reality due to the loss of the solar tide. If you added a 
simple solar tide (i.e a delay factor for the local solar hour-angle and 
a solar-tide amplitude-factor) then you'd probably be getting a pretty 
good rough approximation for a given area. Good enough for a flight-sim, 
certainly.


It would also better model those areas of the world where the solar tide 
dominates and there's only one significant tide per day.


Steve


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