[cad-linux] Re: .dxf or .dwg?

Hi Sagar.

The ways that dxf files are used is really is a kinda database.  It has very 
few different geometric entities, and you can't add other variables to an 
entity or other entities so it is a bit like a primitive kind of Cobol 
database like we might have encountered years ago. (before your time, I 
suspect)

Think of it this way.  When someone draws a part and saves it as dxf, the file 
reflects the order in which the drawing was made.  This is not the order in 
which you will want to cut the part.  A single entity in the drawing may also 
take many passes of a cutter in order to rough out and finish it 
successfully.  If the dxf entities were parsed into a database with each 
having it's own set of variables, including those that you add as you build 
the executable G-Code, you will be building a repeatable CAM file.  You will 
not need to go back and reorder and assign direction each time you open the 
file.

The kinds of entities that you might want to add to a dxf as you prepare it 
for cutting include the kinds of tools that you will be using to do the 
cutting, the roughing and finish cutting characteristics of each tool, etc.  
You will also want to add the paths that the tool will take between drawing 
entities. 

You will also want to add additional variables to each dxf entity.  These will 
include the order of execution of each, the direction of the cut, and any 
"canned" pattern for roughing or repeating a cut with offsets until the dxf 
position variables have been reached.

If you begin the CAM project by saving the dxf into some sort of database, and 
building in and on that database file you will have a much more easily 
expandable project.  

Ray


On Friday 22 August 2003 07:22 am, you wrote:
> Hello again,
> 
> This is going to sound really awkward. I am primarily
> a mechanical engineer, who got pissed off because I
> couldn't find a good gpl'ed cam software. I am not a
> programming guru, so bear with me if this sounds
> stupid. (I got a bunch of computer science students
> who are going to do that actual programming)
> 
> Where exactly and how is a database required in a CAM
> software? Could somebody give a very quick rundown of
> teh steps required to create a cam software? Something
> like
> 
> 1) Read in a .dxf file
> 2) identify arcs, curves blah
> 3) convert them to g-codes
> 4) do something else to modify those g-codes to obtain
> a proper tool path
> 
> well...something like that anyways..
> 
> I saw the source code of a program from Yeager
> automation, called Ace, which accepts a .dxf as input
> and generates g-codes. I am fairly certain that it did
> not incorporate a database, hence my doubt.
> 
> I'd really love to interact more with you guys as the
> software starts taking shape.
> 
> Thanks and regards,
> Sagar
> 
> --- Lee Harding <lee.harding@xxxxxxxxxxxx> wrote:
> > Another option is using PostgreSQL's built-in
> > geometry types.

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