Why does not work using while for looping process - tcl

Question

Why my script does not work. I am using while for looping process.
Hope anyone could help me for my case. The script as below;
Set global
global xmin xmax ymin ymax xVer yVer x1 y1 Count
Set paramaters
set xmin 0
set xmax 51
set ymin 0
set ymax 51
set x1 2
set y1 2
set xVer 2
set yVer 2
set Count 1
set goToVer "n"
Do looping process
while {$x1 > $xmin && $x1 < $xmax && $y1 > $ymin && $y1 < $ymax} {
# For horizontal axis
while {$x1 > $xmin && $x1 < $xmax} {
set azi [expr (45+90)]
set dip 0
set length 2
set dist [expr (cos($dip) * $length)]
set x1 [expr ($x1 + (sin($azimuth) * $dist))]
set y1 [expr ($y1 + (cos($azimuth) * $dist))]
set goToVer "y"
incr Count
}
# For vertical axis
if {$goToVer == "y"} {
set azi 45
set dip 0
set length 5
set dist [expr (cos($dip) * $length)]
set x1 [expr ($xVer + (sin($azimuth) * $dist))]
set y1 [expr ($yVer + (cos($azimuth) * $dist))]
set xVer $x1
set yVer $y1
incr Count
}
}
Thanks in advance!

Answer 1

I don't know what the problem is, but there are some things that we can do to make everything better. First step: let's ry factoring out the coordinate conversion code itself into a little procedure (I've fixed the braces around the expressions too):
proc convert {x y length azimuth dip} {
set dist [expr {cos($dip) * $length}]
set x1 [expr {$x + sin($azimuth) * $dist}]
set y1 [expr {$y + cos($azimuth) * $dist}]
return [list $x1 $y1]
}
while {$x1 > $xmin && $x1 < $xmax && $y1 > $ymin && $y1 < $ymax} {
# For horizontal axis
while {$x1 > $xmin && $x1 < $xmax} {
set azi [expr (45+90)]
set dip 0
set length 2
lassign [convert $x1 $y1 $length $azi $dip] x1 y1
set goToVer "y"
incr Count
}
# For vertical axis
if {$goToVer == "y"} {
set azi 45
set dip 0
set length 5
lassign [convert $xVer $yVer $length $azi $dip] x1 y1
incr Count
}
}
Next, the value of azi in the inner loop is suspicious; it looks like it is in degrees but Tcl's trigonometry functions (like those in most other programming languages) take their argument in radians. Multiply it by π/180°.
Finally, the logic of the loops is weird. I'm not saying it is wrong… but I really find it hard to comprehend what you'd use looping like that for. To loop a pair of coordinates over some space using equal steps on the axes, you use for loops with integer iterator variables and then apply a conversion to get your floating point coordinates (this is best because it limits cumulative errors):
set azi [expr {(45 + 90) * 3.1415927/180}]
set dip 0
set length 2
for {set x $xmin} {$x <= $xmax} {incr x} {
for {set y $ymin} {$y <= $ymax} {incr y} {
set dist [expr {cos($dip) * $length}]
set x1 [expr {$x + sin($azimuth) * $dist}]
set y1 [expr {$y + cos($azimuth) * $dist}]
# I assume you want to do something with $x1,$y1 here…
}
}
Alternatively, you could use regular spacing in polar coordinates, or any other regular scheme; it's just that good code exploits regularity and you're strongly recommended to work that way if you can. But that might not be what you were trying to do at all. Your code is confusing in its intent.
Which brings me to your actual bugs, which appear to revolve around state management. The logic with the goToVer was confused, BTW, and that might've been the problem you were having. You were setting it in the inner loop, but from that point on it was always set. I recommend not doing things like that as it is quite difficult to debug (there are cases where it can make sense, but it doesn't look like you're doing them) and instead sticking to regular grids, but they can work. I'm guessing that you are missing a reset of the variable to 0 at some point in the outer loop, probably just before the inner loop starts.