[pstricks] Re : pst-vue3D: two examples

[hjsalchow at aol.com]

mluque5130 at aol.com schrieb:
>  
> >dear manuel,
> >typical cooling towers hyperbolic structures. See:
>
> >http://en.wikipedia.org/wiki/Hyperboloid_structure
>
> >http://en.wikipedia.org/wiki/Cooling_tower
>
>
>
> >Your example seems to me as a mixture of a hyperbolic structure and a tube.
>
>
> The author of these two splendid examples is Christian Sgraja :
>
> http://www.tug.org/pipermail/pstricks/2006/003384.html
>
>     
> However, I also a little studied the representation of a tower of
> cooling of a nuclear thermal power station with the subscribers of the
> Syracuse list and the photographs of Jean-Michel Sarlat. The
> photographs and the PSTricks examples are here:
>
> http://syracuse.eu.org/~jms/photos/2006/0813-civaux1/
> http://syracuse.eu.org/~jms/photos/2006/0813-civaux2/
>
> http://syracuse.eu.org/syracuse/mluque/
>
> http://syracuse.eu.org/syracuse/mluque/pst-v3d/pst-V3D0.42/tours-civaux/
>
> Manuel 
>  
>
>
>
>
>
> Hans-Juergen Salchow
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>   
Dear Manuel,

looking at your photos from the cooling towers i found two things that may be 
interesting for you:

(1) the contours of the towers are surprisingly well approximated by a single  
bezier curve.   

(2) Since buildings are high and the photograph attempts to show us most details, 
images suffer several distortions (a) from tilting the camera upwards and 
(b) from zooming.  See http://en.wikipedia.org/wiki/Perspective_correction_lens 
how to correct this. However, since the objects are quite big and the shape is simple 
you can do the job without all this equipment if you are aware of the effects. 

That is to say 
(i) take the image from that largest possible distance,

(ii) choose a normal lens (no zoom), and 

(iii) do not tilt the camera upwards.

(iv) Following (i)-(iii) implies that the object will be 
only a small part of the image. Afterwards you will work only 
with this small part of the image. It would be nice to be able 
to magnify this part of the image. Thus the higher the resolution 
of the image the better. Therefore consider taking an old fashioned
analog camera and scanning the magnified towers.

(v) Play with filters to ensure that the towers contrast well 
against the sky.

(vi) Be aware of dust. You may convince the owner to turn off 
the cooling, just for half an hour so that your pictures have 
clear contours, without the usual dust. ;-) If not, be aware 
of the direction of the wind.  

(vii) my preferred picture is 
http://syracuse.eu.org/~jms/photos/2006/0813-civaux1/IMG_1183a.jpg
since it is the most complete view of the (northern?) tower. 
My ideal picture would be something like a non zoomed version of this photo.
This northern tower in the horizontal center of the image. The vertical 
center is out of your control since the camera is upright.  
(to minimize distortion). Choose the distance so that the southern tower 
appears at the right hand side. This is in order to have a second vertical line 
(i.e. the center of the south tower) to control the remaining distortion.

Best regards
Hans-Juergen