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當我計算點和線之間的距離時,我遇到了問題。 有浮點數計算(比較表達式)問題。由於這個原因,我無法知道$ onextensionFlag的完美價值。請看下面... 我可以知道什麼是錯的嗎?在tcl中比較浮點數
proc calculateDistanceToLinefrompoint {P line} {
# solution based on FAQ 1.02 on comp.graphics.algorithms
# L = sqrt((Bx-Ax)^2 + (By-Ay)^2)
# (Ay-Cy)(Bx-Ax)-(Ax-Cx)(By-Ay)
# s = -----------------------------
# L^2
# dist = |s|*L # =>
# | (Ay-Cy)(Bx-Ax)-(Ax-Cx)(By-Ay) |
# dist = ---------------------------------
# L
# (Ay-Cy)(Ay-By)-(Ax-Cx)(Bx-Ax)
# r = -----------------------------
# L^2
# r=0 P = A
# r=1 P = B
# r<0 P is on the backward extension of AB
# r>1 P is on the forward extension of AB
# 0<=r<=1 P is interior to AB
set ret 0
set Ax [lindex $line 0 0]
set Ay [lindex $line 0 1]
set Az [lindex $line 0 2]
set Bx [lindex $line 1 0]
set By [lindex $line 1 1]
set Bz [lindex $line 1 2]
set Cx [lindex $P 0]
set Cy [lindex $P 1]
set Cz [lindex $P 2]
if {$Ax==$Bx && $Ay==$By && $Az==$Bz} {
set ret [list [GetDistanceBetweenTwoPoints $P [lindex $line 0]] 1]
} else {
set L [expr {sqrt(pow($Bx-$Ax,2) + pow($By-$Ay,2) + pow($Bz-$Az,2))}]
#puts "L=$L"
set d_val [expr {($Ay-$Cy)*($Bx-$Ax)-($Ax-$Cx)*($By-$Ay)-($Az-$Bz)*($Az-$Cz)}]
set n_rval [expr {$d_val/pow($L,2)}]
set n_rval [format "%0.3f" $n_rval]
if { 0 < $n_rval && $n_rval < 1} {
set onextensionFlag 0;# inside clipping area
} elseif {$n_rval == 0 || $n_rval == 1} {
set onextensionFlag 1 ;# inside clipping area (but on point)
} elseif { $n_rval > 1 || $n_rval < 0 } {
set onextensionFlag 2 ;# outside clipping area
} else {
set onextensionFlag 3 ;# consider inside clipping area
}
set ret [list [expr {abs($d_val)/$L}] $onextensionFlag $n_rval]
}
}
謝謝。這是我正在尋找的。對我來說非常好的一課。 – OliveOne 2011-03-10 11:54:31
另外,在IEEE浮點(Tcl使用的)中,精確的數字是整個數字,直到相當合理的大小。但不是無限的;雙精度浮點數有固定的位數。 – 2011-03-10 14:01:19