need some help

[johnnash]

i am writing a scientific software in C language which will be use for
calculation of radar cross section of large aerospace/marine objects.
the technique i will be using is ray tracing. The aerospace/marine
objects will be modelled by using NURBS surfaces. So a cad file
containing these geometrical entities will be the input to my
software. My questions are

1. how can i read such cad files in C language ?

2. How do I process the NURBS surfaces ? I mean how should I create a
struct which will deal with each surface ?

Please help me or guide me to a ng where some graphics/c experts may
be able to help.

 

[Billy Bong]

i am writing a scientific software in C language which will be use for
calculation of radar cross section of large aerospace/marine objects.
the technique i will be using is ray tracing. The aerospace/marine
objects will be modelled by using NURBS surfaces. So a cad file
containing these geometrical entities will be the input to my software.
My questions are

1. how can i read such cad files in C language ?

2. How do I process the NURBS surfaces ? I mean how should I create a
struct which will deal with each surface ?

Please help me or guide me to a ng where some graphics/c experts may be
able to help.

Don't even try this in C. Use C++. Here is the definitive site.

http://www.opennurbs.org/

 

[Richard Heathfield]

johnnash said:

i am writing a scientific software in C language which will be use for
calculation of radar cross section of large aerospace/marine objects.
the technique i will be using is ray tracing. The aerospace/marine
objects will be modelled by using NURBS surfaces. So a cad file
containing these geometrical entities will be the input to my
software. My questions are

1. how can i read such cad files in C language ?

http://www.wotsit.org/list.asp?fc=19 provides file format information for a
variety of CAD formats.

2. How do I process the NURBS surfaces ? I mean how should I create a
struct which will deal with each surface ?

http://www.rw-designer.com/NURBS gives some basic information on NURBS
curves. (Don't take that site as gospel, though - it may be that the
graphics guys - see below - have better recommendations.)

Since the number of splines in each curve is variable, I would recommend a
dynamic structure. If you can pin down what information you need to store
and what the variable parts are, we could certainly help you to express
that in C.

Please help me or guide me to a ng where some graphics/c experts may
be able to help.

For the C bits, right here is fine, but first you need to establish exactly
what you're trying to represent and manipulate, and the best place for
that is probably the comp.graphics.algorithms newsgroup.

 

[johnnash]

Don't even try this in C. Use C++. Here is the definitive site.

http://www.opennurbs.org/

Actually, I cannot use C++ as I have been told not to use it but
anyway, thanks for the link.

 

[johnnash]

johnnash said:



http://www.wotsit.org/list.asp?fc=19provides file format information for a
variety of CAD formats.




http://www.rw-designer.com/NURBSgives some basic information on NURBS
curves. (Don't take that site as gospel, though - it may be that the
graphics guys - see below - have better recommendations.)

Since the number of splines in each curve is variable, I would recommend a
dynamic structure. If you can pin down what information you need to store
and what the variable parts are, we could certainly help you to express
that in C.


For the C bits, right here is fine, but first you need to establish exactly
what you're trying to represent and manipulate, and the best place for
that is probably the comp.graphics.algorithms newsgroup.

--
Richard Heathfield <http://www.cpax.org.uk>
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

Hi Richard,

Thanks for the tutorial it was certainly helpful. as far as the C bits
are concerned the only problem I seem to have is as to how I must go
about designing the program. I'm only a intermediate level programmer
and have only 5-6 months of time to finish this huge project(working
full time). So I was wondering as to how I must divide this program
into smaller modules i.e. all the .h files and .c files. Is there any
particular methodology that might help in deciding how I must break
down the problem into smaller pieces ?
Do you know about some ray tracing codes ? Do you think it will help
to go through some of these codes in order to get some idea as to how
I must begin coding ?

 

[Richard Heathfield]

johnnash said:

Thanks for the tutorial it was certainly helpful. as far as the C bits
are concerned the only problem I seem to have is as to how I must go
about designing the program. I'm only a intermediate level programmer
and have only 5-6 months of time to finish this huge project(working
full time). So I was wondering as to how I must divide this program
into smaller modules i.e. all the .h files and .c files. Is there any
particular methodology that might help in deciding how I must break
down the problem into smaller pieces ?

It's impossible to be dogmatic about this, but I would start off by
defining the basic concepts in the system, e.g. functions for manipulating
vectors and NURBS curves would sit very nicely in one module, your
"virtual world" stuff (representations, rotations, translations, scaling)
would make another good one, your rendering buffer routines could make
another, and so on. Let each module stand alone as far as possible. If you
have to combine them, do so by calling those routines from functions
defined in *another* module which, again, is as standalone as possible.

Put the public interface of each module into its own header file.

Do you know about some ray tracing codes ? Do you think it will help
to go through some of these codes in order to get some idea as to how
I must begin coding ?

Your best source of advice on high quality ray tracing code would be
comp.graphics.algorithms.

 

[Malcolm McLean]

i am writing a scientific software in C language which will be use for
calculation of radar cross section of large aerospace/marine objects.
the technique i will be using is ray tracing. The aerospace/marine
objects will be modelled by using NURBS surfaces. So a cad file
containing these geometrical entities will be the input to my
software. My questions are

1. how can i read such cad files in C language ?

2. How do I process the NURBS surfaces ? I mean how should I create a
struct which will deal with each surface ?

Please help me or guide me to a ng where some graphics/c experts may
be able to help.

Is this over your head, or is it helpful?
www.cs.utah.edu/vissim/papers/raynurbs/node3.html

 

[Bartc]

i am writing a scientific software in C language which will be use for
calculation of radar cross section of large aerospace/marine objects.
the technique i will be using is ray tracing. The aerospace/marine
objects will be modelled by using NURBS surfaces. So a cad file
containing these geometrical entities will be the input to my
software. My questions are

1. how can i read such cad files in C language ?

Is this any specific cad file format? If so which one?

What do you mean by ray tracing? That is normally a technique for rendering
a view of the objects.