s
h
o
w
g
r
i
d
r
e
c
t
a
n
g
u
l
a
r
p
o
l
a
r
s
h
o
w
c
o
o
r
d
i
n
a
t
e
s
r
e
c
t
a
n
g
u
l
a
r
p
o
l
a
r
g
r
i
d
s
n
a
p
r
e
c
t
a
n
g
u
l
a
r
p
o
l
a
r
d
o
n
o
t
s
n
a
p
t
o
g
r
i
d
x
=
4
y
=
4
r
=
4
2
=
5
.
6
5
6
8
5
θ
=
π
4
=
0
.
2
5
π