| Re: Image plot on back wall [message #17932] |
Fri, 19 November 1999 00:00 |
davidf
Messages: 2866
Registered: September 1996
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Senior Member |
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Richard G. French (rfrench@wellesley.edu) writes:
>> IT WORKS!
>
> Ok, I'm not going to let you guys off that easily! I've got to see an
> example of this so I can learn how to use the Z buffer, too! Can you
> put together a simple example of this new image plot on the back wall?
> Then the mere mortals among us can try to figure out the coordinate
> transformations and maybe help you avoid having to fiddle it by hand.
> I must say that David's (and Martin's) sample code for object graphics
> has got me quaking in my boots. I'm relieved to know that there is a way
> to do this using direct graphics!
Sorry. raouldukey@my-deja.com has the code. I've got
my tennis racquet and I'm just heading out the door. :-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438 E-Mail: davidf@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155
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| Re: Image plot on back wall [message #17933 is a reply to message #17932] |
Fri, 19 November 1999 00:00  |
Richard G. French
Messages: 65
Registered: June 1997
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Member |
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raouldukey@my-deja.com wrote:
>
> IT WORKS!
>
Ok, I'm not going to let you guys off that easily! I've got to see an
example of this so I can learn how to use the Z buffer, too! Can you
put together a simple example of this new image plot on the back wall?
Then the mere mortals among us can try to figure out the coordinate
transformations and maybe help you avoid having to fiddle it by hand.
I must say that David's (and Martin's) sample code for object graphics
has got me quaking in my boots. I'm relieved to know that there is a way
to do this using direct graphics!
Dick French
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| Re: Image plot on back wall [message #17938 is a reply to message #17932] |
Fri, 19 November 1999 00:00 |
raouldukey
Messages: 15
Registered: November 1999
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Junior Member |
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IT WORKS!
Thanks for the Z buffer tip. I had never used that
before, but now I see all sorts of applications.
Thanks again!
>
> The problem here isn't that Shade_Surf is erasing the
> display, the problem is that it is NOT erasing the
> display. Now are you confused? :-)
>
> The output of Shade_Surf is actually an image. I think
> you could get this program to work if you puts the bits
> and bobs together in the Z graphics buffer. Then things
> that were suppose to be behind other things would actually
> show up there.
>
> Think of the Z-graphics buffer as Object_Graphics Lite
> and you will have no difficulties. :-)
>
> Cheers,
>
> David
>
> --
> David Fanning, Ph.D.
> Fanning Software Consulting
> Phone: 970-221-0438 E-Mail: davidf@dfanning.com
> Coyote's Guide to IDL Programming: http://www.dfanning.com/
> Toll-Free IDL Book Orders: 1-888-461-0155
>
Sent via Deja.com http://www.deja.com/
Before you buy.
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| Re: Image plot on back wall [message #17945 is a reply to message #17932] |
Fri, 19 November 1999 00:00 |
davidf
Messages: 2866
Registered: September 1996
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Senior Member |
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raouldukey@my-deja.com (raouldukey@my-deja.com) writes:
> Ok...so you would think my life is now perfect and that I would
> be satisfied? Not So! It turns out that this method works fine
> if I use the surface procedure to redraw the surface in front
> of the image using the /noerase keyword. However, the shade_surf
> procedure doesn't seem to accept the /noerase keyword (well...it
> accepts it, but just chooses to ignore it ;) ) so it erases
> the screen and redraws the surface. Therefore it erases the
> image I worked so hard to place correctly! *sigh* Of course,
> the shade_surf doesn't seem to be a normal procedure that I
> can attempt to modify so that it behaves more like its brother
> surface.
>
> At this point, I am again stumped. I know that the output
> would look excellent if I could just get it to work. Unless
> there is a way to get shade_surf to recognize /noerase, I
> think I have no choice but to switch to object graphics via
> your example. Thanks for the help, and for giving me a place
> to whine about my IDL difficulties!
The problem here isn't that Shade_Surf is erasing the
display, the problem is that it is NOT erasing the
display. Now are you confused? :-)
The output of Shade_Surf is actually an image. I think
you could get this program to work if you puts the bits
and bobs together in the Z graphics buffer. Then things
that were suppose to be behind other things would actually
show up there.
Think of the Z-graphics buffer as Object_Graphics Lite
and you will have no difficulties. :-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438 E-Mail: davidf@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155
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| Re: Image plot on back wall [message #17946 is a reply to message #17932] |
Fri, 19 November 1999 00:00 |
davidf
Messages: 2866
Registered: September 1996
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Senior Member |
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Martin Schultz (m218003@modell3.dkrz.de) shows that the
Germans do too have a sense of humor when he writes:
> OK. I guess, I see clearer now: it's not objects that I don't like, but
> the applications that are built on objects! ... Nowadays it seems we have to *talk*
> to these machines and *ask* them to *please* try to accomplish at least
> a tiny fraction of what we had in mind.
Even though your program didn't actually produce anything
on the display (typical for object graphics programs,
by the way) when I tried to run on my machine, it did
manage to capture some of the flavor of object graphics
programs. :-)
But RSI never claimed this stuff wasn't low level. They
just haven't come up with much in the way of higher level
tools. And I'm not sure we want them to anyway. Heck, you
will find *much* better IDL programs than RSI puts out
just by looking around the web. How come Liam Gumley
has to write a TV command that actually works on the
machines we run IDL on!? And images are IDL's thing,
for goodness sake.
But to give RSI some credit, they do have new things
in each new release that make object graphics easier
to use. In IDL 5.3, I think (I couldn't get my old
beta fired up for some reason, so I couldn't try this),
they now have these handle-like things you can put
around your lights. Sort of like the lights we use
in the theater. That way you can *see* the lights in
your scene and physically move them around and position
them. That will make things a LOT easier to work with.
The thing that absolutely makes object graphics so
impossible on occasions is that you get absolutely
no feedback on what has gone wrong. Since *everything*
is possible, object graphics doesn't care if you
rotate the surface under the rug where it can't be
seen. Maybe that is where you intended to put it.
Meanwhile you sit and stare at an empty screen for
hours, whispering every incantation you know, hoping
upon hope that *something* might show up to give you
your bearings.
I'm telling you, I only have so much patience for
staring at a black rectangle on the display that is
suppose to be an image. I finally, yesterday, had
to ask RSI for an example that worked. At first
they pointed me to their Show3_Object example
in the example/objects directory, which I had
already examined, since that is exactly what I
was trying to do. But that example worked as
well as mine did: a black rectangle instead of
the image. Don't these people look at the output
of these programs before they pass them off as
examples of how to write programs!?
But eventually I did get a working example. That is
the only way I would have discovered, I think, that
a 24-bit image was required. I tend, like many
people, to be *way* to naive when it comes to
believing what I read.
So, OK, it was a frustrating day. But I learned a
couple of new things, and knowledge that comes
too easy isn't fully appreciated. What I know will
help me sell books. What I can't figure out is why
RSI believes that their customers, who have no
such financial incentive to spend hours learning
this on their own, will be willing (or able) to
give up direct graphics for this.
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438 E-Mail: davidf@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155
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| Re: Image plot on back wall [message #17950 is a reply to message #17932] |
Fri, 19 November 1999 00:00 |
raouldukey
Messages: 15
Registered: November 1999
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Junior Member |
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Wow! Thanks for taking the time to help. I looked at your
"simple" program, and it was impressive. I will try to
work through it and try to learn something about object
graphics, because at this point, they are simply magic
to me.
>
> ftp://ftp.dfanning.com/pub/dfanning/outgoing/misc/example_su rface.pro
>
As for my efforts here, I continued to work with trying to
modify the show3.pro routine, because the output is exactly
what I am looking for, if I can only get control of it.
The coordinate transformations don't seem to be well-documented,
and the IDL manuals aren't that helpful (IMHO).
I was finally able to work out how to project the image to
the front face of the cube. I wasn't able to automatically
work out the coordinates of the back face, so I had to manually
tweak it into position. This isn't too bad, because the coordinates
will always be the same for a given x and z axis rotation.
Ok...so you would think my life is now perfect and that I would
be satisfied? Not So! It turns out that this method works fine
if I use the surface procedure to redraw the surface in front
of the image using the /noerase keyword. However, the shade_surf
procedure doesn't seem to accept the /noerase keyword (well...it
accepts it, but just chooses to ignore it ;) ) so it erases
the screen and redraws the surface. Therefore it erases the
image I worked so hard to place correctly! *sigh* Of course,
the shade_surf doesn't seem to be a normal procedure that I
can attempt to modify so that it behaves more like its brother
surface.
At this point, I am again stumped. I know that the output
would look excellent if I could just get it to work. Unless
there is a way to get shade_surf to recognize /noerase, I
think I have no choice but to switch to object graphics via
your example. Thanks for the help, and for giving me a place
to whine about my IDL difficulties!
Raoul
PS To all - Sorry about the double post yesterday....
strange mixup!
Sent via Deja.com http://www.deja.com/
Before you buy.
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| Re: Image plot on back wall [message #17951 is a reply to message #17932] |
Fri, 19 November 1999 00:00 |
m218003
Messages: 56
Registered: August 1999
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Member |
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In article <MPG.129e62a85186952598997c@news.frii.com>,
davidf@dfanning.com (David Fanning) writes:
> Well, after telling someone the other day,
> "Oh, it would be simple with object graphics.",
> I decided to see how simple it would be.
>
> Yikes!
>
> OK, must be a light problem. Add a light to the image.
> (Why didn't I think of this? Every picture in an
> art gallery has a light above the image to illuminate
> it. Stupid.) Whoops! Wrong kind of light. Add
> *ambient* light there, Jose.
>
> And so it goes. I'm looking for my slide rule right
> now so I can calculate the optimum distance and viewing
> angles for the lights in the scene. [...][/color]
OK. I guess, I see clearer now: it's not objects that I don't like, but
the applications that are built on objects! Just had a look at AVS the other
day: Maybe I'm already too old for this, but I just can't make ends of
something where you have to mouse and drag yourself along, select
rectangles with a 3D-look and inconclusive labels, paste them onto a
worksheet, connect them with wires, and hope that this will work.
Similarily: IDGgr... is far too much "real life oriented" for my sense.
Why should I have to call an electrician (or - worse - a professional light
engineer) just to put some scene on my screen. I always thought, the
virtue of a computer is that you can use it as a tool, and that it will
do *exactly* what you ask it to do. Nowadays it seems we have to *talk*
to these machines and *ask* them to *please* try to accomplish at least
a tiny fraction of what we had in mind.
Even though it might in the end produce a result which falls short of
one produced with IDLgr..., I much prefer to write
surface,data
instead of
virtual_world = obj_new("IDLgr...",/Grass_On_The_Bottom, $
/Mountains_On_The_Right,/Rivers_Below)
virtual_world -> SetProperty,River="blue and reflecting", $
Mountains="not too steep"
light = obj_new("IDLgr...",Time_Of_Year="January 1, 1999 AD", $
Sky="Some scattered Cumulus Clouds")
light -> SetProperty,MoonPhase="Full"
potential_surface_plot = obj_new("IDLgr...",world=virtual_world, $
light=light)
potential_surface_plot -> AddData, data
; In version 5.2.1, rivers don't look nice, so turn them off
potential_surface_plot -> SetProperty,/DoNotShowRiver
; The following feature is undocumented but prevents a crash
; for winter scenes
potential_surface_plot -> SetProperty,/DoNotCareAboutSnowCover
potential_surface_plot -> Please_Show_And_Pray_That_User_Doesnt_Change_Aspect
Ooops! Forgot to specify the density of air .... and my clouds don't
have 24 bit ...
But object graphics programs may win a Noble Price for literature one of these
days ;-)
Cheers,
Martin
--
[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[ [[[[[[[
[[ Dr. Martin Schultz Max-Planck-Institut fuer Meteorologie [[
[[ Bundesstr. 55, 20146 Hamburg [[
[[ phone: +49 40 41173-308 [[
[[ fax: +49 40 41173-298 [[
[[ martin.schultz@dkrz.de [[
[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[ [[[[[[[
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| Re: Image plot on back wall [message #17959 is a reply to message #17932] |
Thu, 18 November 1999 00:00 |
davidf
Messages: 2866
Registered: September 1996
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Senior Member |
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raouldukey@my-deja.com (raouldukey@my-deja.com) writes:
> I thought it would be easy to modify the Show3.pro
> routine to place the image plot on the back wall
> of the cube instead of the floor. However, after
> struggling with it for a long time, I find that
> I am totally confused by the multiple coordinate
> transformations made. Has anyone got
> some tips on how to do this?
>
> What I would like
> is to create the cube with the shaded surface
> command, work out the coordinates of the back
> wall, and use polywarp to work out where to
> project the image. Then, afterwards replace
> the shaded surface on the floor of the cube.
>
> I know....I know.....I need to learn object
> graphics. Any tips would be appreciated!
Well, after telling someone the other day,
"Oh, it would be simple with object graphics.",
I decided to see how simple it would be.
Yikes!
There are just one or two gotchas here that make
life a wee bit difficult at times, starting with
the fact that the documentation is wrong--again.
However, this is the same wrongness I uncovered
in another long, frustrating day not too long ago,
so I think I can now safely offer this rule of
thumb: if the documentation says you can do something
in object graphics with a 2D image, the documentation
is almost certainly wrong. In any case, before you
spend three hours making life miserable for the poor
dog, try it with a 24-bit image. Life will be easier
that way.
OK, so we think we can approach this by rotating
the object image (24-bit, please), but it ain't
so. Images don't rotate in object graphics. (The
documentation does point this out, somewhere.)
So, no problemo. We're gonna make a polygon
object and add the image to it with the Texture_Map
keyword. I've used this for surfaces and it
works like a champ. Very easy.
Except...How come my image is black? :-(
Ah, I need a 24-bit image. Did I mention this?
Ok, 24-bit image, texture map, rockin' and rollin' now.
Except...oough. Still black. Well, not *midnight* black,
but black enough. Let's see. What about if I put the
image here, instead of where I really want it. Humm.
Not so black. What about there? Only black on one
side, but not too bad on the other. Only problem
now is that it's across the street from where I want
it. :-(
OK, must be a light problem. Add a light to the image.
(Why didn't I think of this? Every picture in an
art gallery has a light above the image to illuminate
it. Stupid.) Whoops! Wrong kind of light. Add
*ambient* light there, Jose.
All right! The image is looking gooood. Try to put
a shaded surface in front of it. Uh, oh. That
surface was also looking good before I added that
damn light to see the image. Now it looks like I've
got the stadium lights shining on the surface.
Sure enough. If you want a shaded surface, better
turn the image lights off...
And so it goes. I'm looking for my slide rule right
now so I can calculate the optimum distance and viewing
angles for the lights in the scene. While I futz around
with it, you might want to look at a simple example
of what I came up with. You can find it here:
ftp://ftp.dfanning.com/pub/dfanning/outgoing/misc/example_su rface.pro
In the end, I pretty much decided this is not going to
be what you had in mind. But that's how it goes some
times. Another day, another ... well, dollar's not
right. Another story, I guess. Better than nothing,
and a whole lot more entertaining for the paying
customers. :-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438 E-Mail: davidf@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155
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