Hello group.

I'm working on a 3d model of the planet Earth. I am trying to figure out
how to take this elevation map, turn it into a heightfield and somehow
"wrap" this heightfield around a sphere. but i'm a little stumped, so I
thought I'd tap into the vast knowledge of this collective for guidance.
I humbly ask for your opinion on this matter.

Many thanks in advance,
Bret

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Bret Slivka wrote:
> 
> Hello group.
> 
> I'm working on a 3d model of the planet Earth. I am trying to figure out
> how to take this elevation map, turn it into a heightfield and somehow
> "wrap" this heightfield around a sphere. but i'm a little stumped, so I
> thought I'd tap into the vast knowledge of this collective for guidance.

Features on the surface are under 10 km.  Yet the equator-to-
pole distance is 10 Mm --- 1000 to one.  Therefore for any
real purpose the Earth is smooth -- use textures
instead if you want anything approaching realism.

But this avoids the point...

POV doesn't support general surface extrusions, and mapping of
height fields is a form of surface extrusion.  Or similary,
it doesn't support superlinear transformations, and spherical
mapping is superlinear.  So I don't think there is an easy
answer.

Dan

-- 
http://www.flash.net/~djconnel/

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Bret Slivka wrote:

> I'm working on a 3d model of the planet Earth. I am trying to figure out
> how to take this elevation map, turn it into a heightfield and somehow
> "wrap" this heightfield around a sphere. but i'm a little stumped

As Dan Connelly points out, the surface of the Earth is relatively
smoother than a billiard ball.  The heights of surface features compared
to the radius of the Earth are negligible.  Nonetheless, relief globes
sell well and provide useful info and a pov relief globe would be a good
thing, so here is a little bit of information.

I would need to see the elevation map to tell you for sure how to turn
it into a heightfield, but if brightness corresponds to height, just use
pov to project it on a square as an image map, instead of lights, give
it an ambient 1 finish, and use an orthographic camera with (if you
want, say, 512x512 resolution) up of <0, 512, 0> and right of <512, 0,
0>.  Position the camera at <.50001, .50001, -1> and look_at <.5, .5,
0>.  Use hf_gray_16.  In any case, once you have the heightfield, you
can either:

a) Get a free program from the brilliant John Beale called orb-cyl.  It
can be found at http://shell3.ba.best.com/~beale/ .  Look in the source
code section of the page.  It is available as both source and executable
for dos or linux.  It will do the job, although it will be fairly slow
and memory intensive.  This is probably the current method of choice.

or

b) I have recently been experimenting with a trick using Tmpov, a Win95
custom compile of 3.02 with many extra features available at
http://twysted.net .  It has an hf_height_at command.  You can create
the height field invisibly in some convenient location and use
hf_height_at to read heights of the hf points, which you can then use a
bit of math to project on to a large sphere as spheres, blobs,
cylinders, cones, whatever of appropriate height.  With enough
resolution in the height field, this can give interesting results. 
Again, time and memory can be an issue.  If time and health permit, I
may write an include or at least a tutorial on this subject.

Incidentally, if your elevation map is from a freely available source, I
would like to see a link.  I have been looking for such a map for my own
experiments along these lines.

Jerry Anning
cle### [at] dholcom

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On Sun, 09 Aug 1998 06:49:59 -0500, Dan Connelly <djc### [at] flashnet>
wrote:

>Bret Slivka wrote:
>> 
>> Hello group.
>> 
>> I'm working on a 3d model of the planet Earth. I am trying to figure out
>> how to take this elevation map, turn it into a heightfield and somehow
>> "wrap" this heightfield around a sphere. but i'm a little stumped, so I
>> thought I'd tap into the vast knowledge of this collective for guidance.
>
>Features on the surface are under 10 km.  Yet the equator-to-
>pole distance is 10 Mm --- 1000 to one.  Therefore for any
>real purpose the Earth is smooth -- use textures
>instead if you want anything approaching realism.
>
Erm...how about using the image as a bump map?
Cheers,

Cliff Bowman
Why not pay my 3D Dr Who site a visit at
http://www.geocities.com/Area51/Dimension/7855/
PS change ".duffnet" to ".net" if replying via e-mail

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Jerry Anning wrote:

> Bret Slivka wrote:
>
> > I'm working on a 3d model of the planet Earth. I am trying to figure out
> > how to take this elevation map, turn it into a heightfield and somehow
> > "wrap" this heightfield around a sphere. but i'm a little stumped
>



> Incidentally, if your elevation map is from a freely available source, I
> would like to see a link.  I have been looking for such a map for my own
> experiments along these lines.
>
> Jerry Anning
> cle### [at] dholcom

---  See my post at povray.binaries.images.

I just posted two images.

One to be used as a grey scale height_field map.

The second is a full color overlay scaled the same
for image mapping over the first..

I believe both were generated taking into account
the distortion problem associated with mapping
onto a sphere and have been corrected accordingly.

Respectfully

K.Tyler

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If you want Bret, email me the elevation map.  I can convert it into a mesh
if you want (although the resulting file would have to be in dxf and it
could be very big, at least 2 Mb, to even come close to acheiving the detail
you're looking at).  All the same, I'll pop it into MAX and use the map as a
displacer on a geosphere.

--
Lance Birch
http://come.to/the.zone
Remove the smiley to e-mail.

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Bret Slivka wrote:

> Hello group.
>
> I'm working on a 3d model of the planet Earth. I am trying to figure out
> how to take this elevation map, turn it into a heightfield and somehow
> "wrap" this heightfield around a sphere. but i'm a little stumped, so I
> thought I'd tap into the vast knowledge of this collective for guidance.
> I humbly ask for your opinion on this matter.

Say.. I see this kind of stuff all the time...

Where CAN you get nice elevation maps, that are firendly for POV to use?
There are tons of random map generators, and nice custom map generators like
leveller, but I want the real thing! Most maps like this are in some format
ugly for POV to use.. Any ideas?

Simon
http://home.istar.ca/~sdevet

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Simon de Vet wrote:
> 
> Where CAN you get nice elevation maps, that are firendly for POV to use?
> There are tons of random map generators, and nice custom map generators like
> leveller, but I want the real thing! Most maps like this are in some format
> ugly for POV to use.. Any ideas?

I can't help you with POV-format maps, but for those who don't mind
doing their own conversion, you can find complete one-kilometre
resolution topographic data for the entire land surface of the Earth at
http://edcwww.cr.usgs.gov/landdaac/gtopo30/gtopo30.html .

-- 
Ross Smith ..................................... Wellington, New Zealand
<mailto:r-s### [at] ihugconz> ........ <http://crash.ihug.co.nz/~r-smith/>
   "Remember when we told you there was no future? Well, this is it."
                                                         -- Blank Reg

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Ross Smith wrote:
>  
> I can't help you with POV-format maps, but for those who don't mind
> doing their own conversion, you can find complete one-kilometre
> resolution topographic data for the entire land surface of the Earth at
> http://edcwww.cr.usgs.gov/landdaac/gtopo30/gtopo30.html .

Many utilities exist to do the conversion.  Leveller is probably
the best, as it includes a nice open-GL preview with fly-through
and supports explicit POV-Ray export.

Leveller: 
http://www3.sympatico.ca/tapio.vocadlo/leveller/

Dan

-- 
http://www.flash.net/~djconnel/

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Dan Connelly <djc### [at] flashnet> writes:

> Ross Smith wrote:
> >  
> > I can't help you with POV-format maps, but for those who don't mind
> > doing their own conversion, you can find complete one-kilometre
> > resolution topographic data for the entire land surface of the Earth at
> > http://edcwww.cr.usgs.gov/landdaac/gtopo30/gtopo30.html .
> 
> Many utilities exist to do the conversion.  Leveller is probably
> the best, as it includes a nice open-GL preview with fly-through
> and supports explicit POV-Ray export.

No, actually, Leveller isn't the best, as it's windows only. Not to
denigrate the author, but no program designed for use with POVray can
honestly claim the title 'the best' unless it runs on at *least* a
significant subset of the systems POVray does.
Leveller seems nice, and I'd like to see an X version of it, but until
there is one, 'the best' would have to be one of the command line
converters that will run on either unix or windows.

Shalon Wood

-- 
People who do stupid things with hazardous materials often die.
--Jim Davidson on alt.folklore.urban

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