1. Re: mathmatical question... to Jiri - Reply
Hi everybody,
I had a second (longer) look at my inside() function last night, and as a result
I have to ingests a bit of a humble pie. While the simple version below works
well for all interior points, it leaves the points on the polygon's periphery
indeterminate. The longer version will include all such points. Jiri
-- inpoly.ex -------------------------------------------------------------------
-- j.babor at gns.cri.nz
--------------------------------------------------------------------------------
include graphics.e
include get.e
object junk
sequence s,tp
integer key
function simple_inside(sequence p, sequence P)
atom x
integer count,n
n=length(P)
P=append(P,P[1])
count=0
for i=1 to n do
if (P[i][2]<=p[2] and P[i+1][2]>p[2]) or (P[i][2]>p[2] and P[i+1][2]<=p[2]
) then
x=P[i][1]+(p[2]-P[i][2])*(P[i+1][1]-P[i][1])/(P[i+1][2]-P[i][2])
if x<p[1] then
count=count+1
end if
end if
end for
return remainder(count,2) -- return 1 (true) if count is odd
end function
function inside(sequence p, sequence P)
atom x
integer count,n
n=length(P)
P=append(P,P[1])
count=0
for i=1 to n do
if not compare(p,P[i]) then
return 1 -- include all vertices
elsif p[2]=P[i][2] and p[2]=P[i+1][2] and ((p[1]>P[i][1] and
p[1]<P[i+1][1]) or (p[1]<P[i][1] and p[1]>P[i+1][1])) then
return 1 -- include all points on horizontal polygon sides
end if
if (P[i][2]<=p[2] and P[i+1][2]>p[2]) or (P[i][2]>p[2] and P[i+1][2]<=p[2]
) then
x=P[i][1]+(p[2]-P[i][2])*(P[i+1][1]-P[i][1])/(P[i+1][2]-P[i][2])
if x=p[1] then
return 1 -- include all points on non-horizontal polygon sides
elsif x<p[1] then
count=count+1
end if
end if
end for
return remainder(count,2) -- return 1 (true) if count is odd
end function
-- main ------------------------------------------------------------------------
junk=graphics_mode(18)
{100,180},{205,190},{190,200},{40,240},{100,240},{200,240},{40,280},
{80,280},{160,280},{180,280},{60,320}}
0,180}}
polygon(1,1,s)
for i=1 to length(tp) do
pixel(15,tp[i])
print(1,inside(tp[i],s))
if not remainder(i,4) then puts(1,"\n") end if
end for
key = wait_key()
junk=graphics_mode(-1)
