Gnuplot: Respect depthorder for Gnuplot 3d polygons

Question

I have a 3D model of a complete city, and would like to show an isometric view of those buildings. I use gnuplot polygons for this, since I don\'t think I can use pm3d for p

Answer 1

I could not find an option to convince gnuplot that it should set the depthorder of the polygon objects automatically. The only way I found was to already define the objects in the correct order. Then gnuplot draws each of them on top of the previous one which leads to the expected result.

Taking your example polygons after removing the front specifiers, this approach changes the original picture from this one:

to this one (after removing front):

to this one (after sorting):

I think the third picture is what you want.

I used a python script to sort the polygons, which basically does:

• Read all polygons from a file "poly_raw.dat". The file must start with a set object x polygon from line.
• Like gnuplot with set view theta, phi, it rotates the polygons around x and z axis (temporarily, just for sorting).
• It sorts the polygons with respect to the new y-axis. This should be the axis which is orthogonal to the screen.
• It updates the gnuplot object IDs, i.e. the x in set object x polygon.
• It prints the sorted polygon data including the set object lines.

Notice that this approach only works for static pictures. It does not work if you want to interactively rotate the picture.

Also notice, if the approach does not work for your full data file, I have probably messed up the rotation matrix or the axis assignment :)

I attach the python script, the plot file, and the data files "plot_raw.dat" and "plot_sorted.dat" for reference.

# poly.py
from math import cos, sin, pi
from re import sub, match, findall

class Polygon:

   def __init__(self):

      self.firstLine = ""
      self.points = []
      self.lastLine = ""


   def __str__(self):

      pointStrings = [",".join(map(str,point)) for point in self.points]

      s = ""
      s += self.firstLine
      s += " to \\\n".join(pointStrings)
      s += "\n"
      s += self.lastLine

      return s


   def readObjectFromFile(self, f, firstObjectLine):
      self.firstLine = firstObjectLine
      line = f.readline()
      while not match("set",line):
         coordinates = findall("[\d.]+", line)
         coordinates = tuple(float(x) for x in coordinates)
         self.points.append(coordinates)
         line = f.readline()
      self.lastLine = line

      return self


   def meanAfterRotation(self, theta, phi):
      cx = 0.0
      cy = 0.0
      cz = 0.0

      theta = theta*pi/180.0
      phi = phi*pi/180.0

      for point in self.points:
         x,y,z = point
         x,y,z = (x, y*cos(theta) - z*sin(theta), y*sin(theta) + z*cos(theta))
         x,y,z = (x*cos(phi) - y*sin(phi), x*sin(phi) + y*cos(phi), z)
         cx, cy, cz = (cx + x, cy + y, cz + z)

      n = len(self.points)

      return (cx/n, cy/n, cz/n)


   def setPosition(self, posIndex):

      self.firstLine = sub("(\d+)", str(posIndex), self.firstLine, 1)
      self.lastLine = sub("(\d+)", str(posIndex), self.lastLine, 1)




polygons = []
with open("poly_raw.dat") as f:

    line = f.readline()
    while line:

       if line.strip() != "":
          polygons.append(Polygon().readObjectFromFile(f,line))

       line = f.readline()

polygons.sort(key = lambda x: x.meanAfterRotation(60,30)[1], reverse = True)
pos = 1
for p in polygons:
   p.setPosition(pos)
   pos += 1

for p in polygons:
   print(p)

The gnuplot script:

# poly.plt, gnuplot 4.6
# Does not work when interactively rotating the picture.

set style line 1 linecolor rgbcolor "#777777" linewidth 1
set style increment user
set palette file "-"
0.00000 0.23137 0.22353 0.64314
0.17990 0.47843 0.34510 0.71765
0.32010 0.34902 0.17647 0.55686
0.43990 0.40784 0.10980 0.36471
0.59010 0.46275 0.09020 0.16863
0.78000 0.86667 0.41569 0.24314
0.92990 0.92549 0.66667 0.33725
1.00000 0.97647 0.91765 0.82745
e
set cbrange [50:150]
set cbtics 25
set format cb "%.0f W/m²"
unset xtics
unset ytics
unset ztics
unset border
set colorbox

kzoom=1.0
phi=30.0
theta=60.0
set xyplane 0       # removes the offset of the xy plane
set view equal xyz  # force equal units to all three axes
set view theta,phi,kzoom

#load "poly_raw.dat"
load "poly_sorted.dat"

set terminal png
#set output "raw.png"
set output "sorted.png"
splot "-" with lines notitle ls 1, NaN notitle palette
2.0 0.0 0.0
2.0 2.0 0.0
4.0 2.0 0.0
4.0 0.0 0.0
2.0 0.0 0.0

0.0 0.0 0.0
0.0 2.0 0.0
2.0 2.0 0.0
2.0 0.0 0.0
0.0 0.0 0.0
e

The unsorted polygon data after removing the front specifiers:

set object 1 polygon from \
2.0,0.0,3.0 to \
3.0,0.0,3.5 to \
3.0,2.0,3.5 to \
2.0,2.0,3.0 to \
2.0,0.0,3.0
set object 1 fill solid 0.9 border lw 2 fc palette cb 128.1315

set object 2 polygon from \
4.0,0.0,3.0 to \
4.0,2.0,3.0 to \
3.0,2.0,3.5 to \
3.0,0.0,3.5 to \
4.0,0.0,3.0
set object 2 fill solid 0.9 border lw 2 fc palette cb 128.62192

set object 3 polygon from \
2.0,0.0,0.0 to \
4.0,0.0,0.0 to \
4.0,0.0,3.0 to \
3.0,0.0,3.5 to \
2.0,0.0,3.0 to \
2.0,0.0,0.0
set object 3 fill solid 0.9 border lw 2 fc palette cb 100.545204

set object 4 polygon from \
4.0,0.0,0.0 to \
4.0,2.0,0.0 to \
4.0,2.0,3.0 to \
4.0,0.0,3.0 to \
4.0,0.0,0.0
set object 4 fill solid 0.9 border lw 2 fc palette cb 85.58082

set object 5 polygon from \
4.0,2.0,0.0 to \
2.0,2.0,0.0 to \
2.0,2.0,3.0 to \
3.0,2.0,3.5 to \
4.0,2.0,3.0 to \
4.0,2.0,0.0
set object 5 fill solid 0.9 border lw 2 fc palette cb 55.88219

set object 6 polygon from \
2.0,2.0,0.0 to \
2.0,0.0,0.0 to \
2.0,0.0,3.0 to \
2.0,2.0,0.0
set object 6 fill solid 0.9 border lw 2 fc palette cb 85.25754

set object 7 polygon from \
2.0,2.0,0.0 to \
2.0,0.0,3.0 to \
2.0,2.0,3.0 to \
2.0,2.0,0.0
set object 7 fill solid 0.9 border lw 2 fc palette cb 85.25754

set object 8 polygon from \
0.0,0.0,3.0 to \
1.0,0.0,3.5 to \
1.0,2.0,3.5 to \
0.0,2.0,3.0 to \
0.0,0.0,3.0
set object 8 fill solid 0.9 border lw 2 fc palette cb 128.1315

set object 9 polygon from \
2.0,0.0,3.0 to \
2.0,2.0,3.0 to \
1.0,2.0,3.5 to \
1.0,0.0,3.5 to \
2.0,0.0,3.0
set object 9 fill solid 0.9 border lw 2 fc palette cb 128.62192

set object 10 polygon from \
0.0,0.0,0.0 to \
2.0,0.0,0.0 to \
2.0,0.0,3.0 to \
1.0,0.0,3.5 to \
0.0,0.0,3.0 to \
0.0,0.0,0.0
set object 10 fill solid 0.9 border lw 2 fc palette cb 100.545204

set object 11 polygon from \
2.0,0.0,0.0 to \
2.0,2.0,0.0 to \
2.0,2.0,3.0 to \
2.0,0.0,3.0 to \
2.0,0.0,0.0
set object 11 fill solid 0.9 border lw 2 fc palette cb 85.58082

set object 12 polygon from \
2.0,2.0,0.0 to \
0.0,2.0,0.0 to \
0.0,2.0,3.0 to \
1.0,2.0,3.5 to \
2.0,2.0,3.0 to \
2.0,2.0,0.0
set object 12 fill solid 0.9 border lw 2 fc palette cb 55.88219

set object 13 polygon from \
0.0,2.0,0.0 to \
0.0,0.0,0.0 to \
0.0,0.0,3.0 to \
0.0,2.0,0.0
set object 13 fill solid 0.9 border lw 2 fc palette cb 85.25754

set object 14 polygon from \
0.0,2.0,0.0 to \
0.0,0.0,3.0 to \
0.0,2.0,3.0 to \
0.0,2.0,0.0
set object 14 fill solid 0.9 border lw 2 fc palette cb 85.25754

The sorted data after running python poly.py > poly_sorted.dat

set object 1 polygon from \
4.0,0.0,0.0 to \
4.0,2.0,0.0 to \
4.0,2.0,3.0 to \
4.0,0.0,3.0 to \
4.0,0.0,0.0
set object 1 fill solid 0.9 border lw 2 fc palette cb 85.58082

set object 2 polygon from \
4.0,2.0,0.0 to \
2.0,2.0,0.0 to \
2.0,2.0,3.0 to \
3.0,2.0,3.5 to \
4.0,2.0,3.0 to \
4.0,2.0,0.0
set object 2 fill solid 0.9 border lw 2 fc palette cb 55.88219

set object 3 polygon from \
2.0,2.0,0.0 to \
2.0,0.0,0.0 to \
2.0,0.0,3.0 to \
2.0,2.0,0.0
set object 3 fill solid 0.9 border lw 2 fc palette cb 85.25754

set object 4 polygon from \
2.0,2.0,0.0 to \
2.0,0.0,3.0 to \
2.0,2.0,3.0 to \
2.0,2.0,0.0
set object 4 fill solid 0.9 border lw 2 fc palette cb 85.25754

set object 5 polygon from \
2.0,0.0,0.0 to \
2.0,2.0,0.0 to \
2.0,2.0,3.0 to \
2.0,0.0,3.0 to \
2.0,0.0,0.0
set object 5 fill solid 0.9 border lw 2 fc palette cb 85.58082

set object 6 polygon from \
2.0,2.0,0.0 to \
0.0,2.0,0.0 to \
0.0,2.0,3.0 to \
1.0,2.0,3.5 to \
2.0,2.0,3.0 to \
2.0,2.0,0.0
set object 6 fill solid 0.9 border lw 2 fc palette cb 55.88219

set object 7 polygon from \
2.0,0.0,0.0 to \
4.0,0.0,0.0 to \
4.0,0.0,3.0 to \
3.0,0.0,3.5 to \
2.0,0.0,3.0 to \
2.0,0.0,0.0
set object 7 fill solid 0.9 border lw 2 fc palette cb 100.545204

set object 8 polygon from \
0.0,2.0,0.0 to \
0.0,0.0,0.0 to \
0.0,0.0,3.0 to \
0.0,2.0,0.0
set object 8 fill solid 0.9 border lw 2 fc palette cb 85.25754

set object 9 polygon from \
4.0,0.0,3.0 to \
4.0,2.0,3.0 to \
3.0,2.0,3.5 to \
3.0,0.0,3.5 to \
4.0,0.0,3.0
set object 9 fill solid 0.9 border lw 2 fc palette cb 128.62192

set object 10 polygon from \
0.0,2.0,0.0 to \
0.0,0.0,3.0 to \
0.0,2.0,3.0 to \
0.0,2.0,0.0
set object 10 fill solid 0.9 border lw 2 fc palette cb 85.25754

set object 11 polygon from \
0.0,0.0,0.0 to \
2.0,0.0,0.0 to \
2.0,0.0,3.0 to \
1.0,0.0,3.5 to \
0.0,0.0,3.0 to \
0.0,0.0,0.0
set object 11 fill solid 0.9 border lw 2 fc palette cb 100.545204

set object 12 polygon from \
2.0,0.0,3.0 to \
3.0,0.0,3.5 to \
3.0,2.0,3.5 to \
2.0,2.0,3.0 to \
2.0,0.0,3.0
set object 12 fill solid 0.9 border lw 2 fc palette cb 128.1315

set object 13 polygon from \
2.0,0.0,3.0 to \
2.0,2.0,3.0 to \
1.0,2.0,3.5 to \
1.0,0.0,3.5 to \
2.0,0.0,3.0
set object 13 fill solid 0.9 border lw 2 fc palette cb 128.62192

set object 14 polygon from \
0.0,0.0,3.0 to \
1.0,0.0,3.5 to \
1.0,2.0,3.5 to \
0.0,2.0,3.0 to \
0.0,0.0,3.0
set object 14 fill solid 0.9 border lw 2 fc palette cb 128.1315