On 10/14/2022 2:35 AM, Max Chernoff via ntg-context wrote:
Hi,
The angle function doesn't appear to provide the same calculation as
my atantwo in all cases.
They both give the same results, but "angle" gives a result in degrees
while "atantwo" gives a result in radians. This demo:
\startMPpage
vardef atantwo( expr dy, dx ) =
save theta;
numeric theta;
theta := 0;
if (dx > 0):
theta := atan( dy / dx );
elseif (dx < 0) and (dy >= 0):
theta := atan( dy / dx ) + pi;
elseif (dx < 0) and (dy < 0):
theta := atan( dy / dx ) - pi;
elseif (dx == 0) and (dy > 0):
theta := pi / 2;
elseif (dx == 0) and (dy < 0):
theta := -pi / 2;
fi;
theta
enddef;
def showangles(expr dx, dy) =
message "---------------"
message "atantwo " & decimal atantwo(dy, dx)
message "angle " & decimal (angle(dx, dy) * pi / 180)
message "angle " & decimal angle(dx, dy)
message "(" & decimal dx & ", " & decimal dy & ")"
enddef;
showangles(1, 0);
showangles(1, 1);
showangles(0, 1);
showangles(-1, 1);
showangles(-1, 0);
showangles(-1, -1);
showangles(0, -1);
showangles(1, -1);
\stopMPpage
So you suggest to add atantwo? As side note, you can redure your
definition to:
vardef atantwo( expr dy, dx ) =
if (dx > 0):
atan( dy / dx )
elseif (dx < 0) and (dy >= 0):
atan( dy / dx ) + pi
elseif (dx < 0) and (dy < 0):
atan( dy / dx ) - pi
elseif (dx == 0) and (dy > 0):
pi / 2
elseif (dx == 0) and (dy < 0):
-pi / 2
else :
0
fi
enddef ;
and then
vardef atantwo(expr dy, dx) =
if dx == 0 :
if dy < 0 : - fi pi / 2
else :
atan(dy/dx) if dx > 0 : if dy < 0 : - else : + fi pi fi
fi
enddef ;
going further makes us end up in an one-line obscurity
Hans
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