Calculate Polygon Boundary using Fixed Boundary Constraints and a Target Area
Hi Dan,
Ok, here's an example of a shape (the selected one). Say you wanted to use the current shape but reduce the amount of area in a straight E-W slice moving southward from the top, being faithful to the outside borders.
Alternatively, say you wanted to add area to the polygon by filling in the empty space between the selected polygon and the red polygon.
Are there good ways to do this? What do you mean, to extend the back line? How would you do this to reach the desired area?
That is an interesting problem.
The "back" line is your top. So effectively, you want to start moving a line parallel to the bottom of your green area.
Here is an example of how the splitting and area calculations will go. I use numpy and arcpy, so bear with me.
K #---- a polygon in the shape of the letter K
array([[ 0.00, 0.00],
[ 2.00, 10.00],
[ 4.00, 10.00],
[ 3.00, 5.00],
[ 6.00, 10.00],
[ 8.00, 10.00],
[ 5.00, 4.00],
[ 6.00, 0.00],
[ 4.00, 0.00],
[ 3.00, 3.00],
[ 2.00, 0.00],
[ 0.00, 0.00]])
# ---- now a cutting polyline parallel to the x-axis
p_line = np.array([[-1., 7.], [11., 7.]])
# ---- create some arcpy geometries
SR = "NAD 1983 CSRS MTM 9"
pgon = Polygon(Array([Point(*xy) for xy in K]), SR) # --- polygon
pline = Polyline(Array([Point(*xy) for xy in p_line]), SR) # --- cutter polyline
#
# ----- time to slice and dice
pgon.area # --- polygons area first
43.0
# --- cut the polygon to yield a top and bottom part
bits = pgon.cut(pline)
# --- area calculations for the bits
bits[0].area
12.449999999720603
bits[1].area
30.549999998882413Now the images before and after splitting
Now the cutting and area calculations can obviously be put into a loop stopping when your desired area is obtained.
As for the second options, I would modify the original polygon and extend the vertical eastern line northward until the green-red area is filled in, and repeat the procedure.
Hope this gives you some ideas.
