The whole task is to convert a CAD data file (of polygonal 3D-model) from
one format into another. I had no problem making that in C++ for my work,
then I decided to program the task in J just for learning it.
Both input and output data files contain two blocks: points and polygons (3-
and 4-angled).
The input file first contains many data, unnecessary for the output file, so
it should be skipped. Then there is a something like:
*NODE
100005-232.27999877930-422.06298828125 22.000000000000 0 0
100006-234.33399963379-381.77999877930 22.000000000000 0 0
100008-269.00201416016-379.25601196289 22.000000000000 0 0
......
......
$
This is the points definition. 8 characters - point ID, then 16x3 - x, y and
z coordinates, then 8x2 - should be skipped. So, I need to read a part of
the file from *NODE till the following '$' character (there are many '$'
both before and after that block of data, so I can not use just any '$' as a
delimiter), then split the strings by 8-16-16-16 pattern (rows are delimited
by CR or CRLF, but there are no delimiters in a row, we can only count the
characters).
Then somewhere later in the file is a block like:
*ELEMENT_SHELL
$ eid pid n1 n2 n3 n4
1 100 110095 110099 110103 110022
2 100 110164 110162 110175 110176
3 100 110175 110158 110157 110177
....
*END
These are the polygons. Each value takes 8 chars here. The first two should
be skipped. The next four are references to the IDs of points, defined
earlier. If all four are different, then it is a quadrangle, if the last two
are identical - a triangle (that's what my original question was concerned
about).
The output file format is like this:
POINTS 1206 float
-232.27999877930 -422.06298828125 22.000000000000
-234.33399963379 -381.77999877930 22.000000000000
-269.00201416016 -379.25601196289 22.000000000000
....
....
POLYGONS 1212 5916
4 104 108 112 31
4 173 171 184 185
4 184 167 166 186
3 719 494 508
3 714 717 715
3 676 492 491
The fields in a string are delimited by space, and no matter how many
characters they contain.
Here 1206 is the number of points, 1212 - the number of polygons, 5916 is
the number all fields used to define the polygons (i.e., 5*number_of_4angles
+ 4*number_of_3angles). The points has no explicitly defined IDs, as in the
input file, so in the output point IDs are always start with 0 and grows by
1. So, the IDs from the input file should be changed to define the polygons
in the output (for this particular examples 100005 will become 0, 100006 -
1, 100008 - 2 etc.). And in the strings after POLYGONS... first comes number
of vertices (3 or 4), and then these changed point ids.
So, I've written:
load 'files'
a =. 'b' fread inputfilename
node_start =. 1 + (s: a) (e.i.1:) (s: ' *NODE')
node_end =. (s:(node_start }. a)) (e.i.1:) (s: ' $')
n_d =: node_end {. node_start }. a
n_d =: 0 ". (4 16)$"1(' ',"1((8+3*16){."1>n_d))
element_shell_start =. 2 + (s: a) (e.i.1:) (s: ' *ELEMENT_SHELL')
element_shell_end =. (s:(element_shell_start }. a)) (e.i.1:) (s: ' *END')
e_s_d =: element_shell_end {. element_shell_start }. a
e_s_d =: 0 ". (4 8)$"1((2*8)}."1>e_s_d)
which read (more than really necessary of) the data, split it and convert it
to numbers (and which also happened to be my first J program). But I
couldn't go any further yet.
From: " Bj?rn Helgason " <[EMAIL PROTECTED]>
Subject: Re: [Jprogramming] Jagged array
To understand your problem
Do you need the data in the changed form
that is do you need the line 61 71 73 to exist after your operation
or
is it just a temporary operation and what you really need is to know if
the two last numbers are equal so you can report 3 or 4?
If it is the latter and you want to just find out 3 or 4 but not needing
to
do the compare you might add a fifth column to hold the number 3 or 4 as
appropriate - assuming that the matrix needs to be around after the
operation of course
Then you could either keep the fourth item in case they are equal or
replace
it with something else
It is always better to know the whole prcocess and not just subtask whic
may
or may not be needed
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