Compas_ags problem

A branching tree with prescribed load to keep it in only compression, single ‘‘foot support’’ and on support at a symmetri line to the right at the top.
So I did a branching tree GH and baked the model --> obj-file --> compas_ags… and receive something that seems reasonable.

But when I subdivide my internal convex polygons again an export them I get this:

Which clearly is not the same external space I started with and some lines are not anymore parallell…

How come?

Py


“”"Compute the equilibrium of a simple statically determined system and
visualise the result using a form and force diagram.

author: Tom Van Mele
email: vanmelet@ethz.ch

“”"
from future import print_function
from future import absolute_import
from future import division

import compas
import compas_ags

from compas_ags.diagrams import FormDiagram
from compas_ags.diagrams import ForceDiagram
from compas_ags.viewers import Viewer
from compas_ags.ags import graphstatics
from compas_ags.ags import loadpath

form = FormDiagram.from_obj(compas_ags.get(‘paper/Branching_tree_sub6.obj’))
force = ForceDiagram.from_formdiagram(form)

form.set_edge_force_by_index(52, -3.0)
form.set_edge_force_by_index(53, -3.0)
form.set_edge_force_by_index(54, -3.0)
form.set_edge_force_by_index(0, -3.0)
form.set_edge_force_by_index(55, -3.0)
form.set_edge_force_by_index(56, -3.0)
form.set_edge_force_by_index(57, -3.0)
form.set_edge_force_by_index(58, -3.0)
form.set_edge_force_by_index(2, -10)
form.set_edge_force_by_index(4, -10)

graphstatics.form_update_q_from_qind(form)
graphstatics.force_update_from_form(force, form)

left = list(form.vertices_where({‘x’: 14.8256, ‘y’: 1.862}))[0]
right = list(form.vertices_where({‘x’: 37.5, ‘y’: 26.6875}))[0]

loadpath.compute_internal_work(form, force)

#loadpath.compute_internal_work(form, force)

viewer = Viewer(form, force, delay_setup=False)

viewer.draw_form(
vertexsize=0.01,
vertexcolor={key: ‘#000000’ for key in (left, right)},
vertexlabel={key: key for key in form.vertices()},
#edgelabel={uv: index for index, uv in enumerate(form.edges())}
)

viewer.draw_force(
vertexsize=0.01,
vertexlabel={key: key for key in force.vertices()}
)
viewer.show()

obj-file


v 17.5 26.1875 0
v 17.5 24.1875 0
cstype bspline
deg 1
curv 0 2 1 2
parm u 0 0 2 2
end
v 0 22 0
v 2.5 22.3125 0
cstype bspline
deg 1
curv 0 5.038911092686593 3 4
parm u 0 0 5.038911092686593 5.038911092686593
end
v 37.5 26.6875 0
v 40 27 0
cstype bspline
deg 1
curv 0 5.038911092686593 5 6
parm u 0 0 5.038911092686593 5.038911092686593
end
v 12.5 23.5625 0
v 17.5 24.1875 0
cstype bspline
deg 1
curv 0 5.038911092686593 7 8
parm u 0 0 5.038911092686593 5.038911092686593
end
v 17.5 24.1875 0
v 22.5 24.8125 0
cstype bspline
deg 1
curv 0 5.038911092686593 9 10
parm u 0 0 5.038911092686593 5.038911092686593
end
v 23.7904 19.833 0
v 23.35828 23.998725 0
cstype bspline
deg 1
curv 0 3.565001139500661 11 12
parm u 0 0 3.565001139500661 3.565001139500661
end
v 26.34512 20.0024 0
v 34.1978 25.096625 0
cstype bspline
deg 1
curv 0 6.744135182228303 13 14
parm u 0 0 6.744135182228303 6.744135182228303
end
v 26.34512 20.0024 0
v 26.65253109006722 21.08466494261383 0
cstype bspline
deg 1
curv 0 1.12507732370146 15 16
parm u 0 0 1.12507732370146 1.12507732370146
end
v 23.7904 19.833 0
v 25.15513594845547 20.99743804116072 0
cstype bspline
deg 1
curv 0 1.793995585476415 17 18
parm u 0 0 1.793995585476415 1.793995585476415
end
v 26.65253109006722 21.08466494261383 0
v 31.96788 24.860725 0
cstype bspline
deg 1
curv 0 4.820642475380392 19 20
parm u 0 0 4.820642475380392 4.820642475380392
end
v 25.15513594845547 20.99743804116072 0
v 25.96796 24.153575 0
cstype bspline
deg 1
curv 0 4.195738723095258 21 22
parm u 0 0 4.195738723095258 4.195738723095258
end
v 25.15513594845547 20.99743804116072 0
v 26.65253109006722 21.08466494261383 0
cstype bspline
deg 1
curv 0 2.560330181519567 23 24
parm u 0 0 2.560330181519567 2.560330181519567
end
v 9.705991817341154 20.07904692995786 0
v 10.23328 18.7881 0
cstype bspline
deg 1
curv 0 1.394480836562231 25 26
parm u 0 0 1.394480836562231 1.394480836562231
end
v 12.58047513328181 20.03731579199177 0
v 13.82568 18.73735 0
cstype bspline
deg 1
curv 0 1.800123945856912 27 28
parm u 0 0 1.800123945856912 1.800123945856912
end
v 13.82568 18.73735 0
v 16.02804 22.953925 0
cstype bspline
deg 1
curv 0 3.833757225752144 29 30
parm u 0 0 3.833757225752144 3.833757225752144
end
v 10.23328 18.7881 0
v 4.548360000000001 21.690325 0
cstype bspline
deg 1
curv 0 4.98090681801846 31 32
parm u 0 0 4.98090681801846 4.98090681801846
end
v 12.58047513328181 20.03731579199177 0
v 13.35828 22.748725 0
cstype bspline
deg 1
curv 0 3.147677116613897 33 34
parm u 0 0 3.147677116613897 3.147677116613897
end
v 9.705991817341154 20.07904692995786 0
v 12.58047513328181 20.03731579199177 0
cstype bspline
deg 1
curv 0 3.592758455908219 35 36
parm u 0 0 3.592758455908219 3.592758455908219
end
v 9.705991817341154 20.07904692995786 0
v 7.49796 21.844825 0
cstype bspline
deg 1
curv 0 2.723114987051185 37 38
parm u 0 0 2.723114987051185 2.723114987051185
end
v 12.120592 16.95984 0
v 15.7768 11.5485 0
cstype bspline
deg 1
curv 1.796379227954109 6.355502557893757 39 40
parm u 1.796379227954109 1.796379227954109 6.355502557893757 6.355502557893757
end
v 15.7768 11.5485 0
v 16.51223928043446 12.96773729794315 0
cstype bspline
deg 1
curv 0 1.598469719162337 41 42
parm u 0 0 1.598469719162337 1.598469719162337
end
v 16.51223928043446 12.96773729794315 0
v 13.916792 16.934465 0
cstype bspline
deg 1
curv 6.355502557893757 10.07996337715673 43 44
parm u 6.355502557893757 6.355502557893757 10.07996337715673 10.07996337715673
end
v 18.1096 11.5545 0
v 23.634168 17.457985 0
cstype bspline
deg 1
curv 0 4.381756070385022 45 46
parm u 0 0 4.381756070385022 4.381756070385022
end
v 17.79949959711237 13.18530242188871 0
v 22.356808 17.373285 0
cstype bspline
deg 1
curv 0 5.02008592780044 47 48
parm u 0 0 5.02008592780044 5.02008592780044
end
v 17.79949959711237 13.18530242188871 0
v 18.1096 11.5545 0
cstype bspline
deg 1
curv 0 1.660023734501751 49 50
parm u 0 0 1.660023734501751 1.660023734501751
end
v 16.51223928043446 12.96773729794315 0
v 17.79949959711237 13.18530242188871 0
cstype bspline
deg 1
curv 0 2.332807716036621 51 52
parm u 0 0 2.332807716036621 2.332807716036621
end
v 22.356808 17.373285 0
v 23.7904 19.833 0
cstype bspline
deg 1
curv 0 5.693991184991066 53 54
parm u 0 0 5.693991184991066 5.693991184991066
end
v 23.634168 17.457985 0
v 26.34512 20.0024 0
cstype bspline
deg 1
curv 0 7.435942021971125 55 56
parm u 0 0 7.435942021971125 7.435942021971125
end
v 22.356808 17.373285 0
v 23.634168 17.457985 0
cstype bspline
deg 1
curv 5.02008592780044 6.300251018560223 57 58
parm u 5.02008592780044 5.02008592780044 6.300251018560223 6.300251018560223
end
v 14.8256 1.862 0
v 18.1096 11.5545 0
cstype bspline
deg 1
curv 0 10.23372914679688 59 60
parm u 0 0 10.23372914679688 10.23372914679688
end
v 14.8256 1.862 0
v 15.7768 11.5485 0
cstype bspline
deg 1
curv 0 9.733091168277424 61 62
parm u 0 0 9.733091168277424 9.733091168277424
end
v 12.120592 16.95984 0
v 10.23328 18.7881 0
cstype bspline
deg 1
curv 0 5.255275906341742 63 64
parm u 0 0 5.255275906341742 5.255275906341742
end
v 13.916792 16.934465 0
v 13.82568 18.73735 0
cstype bspline
deg 1
curv 0 3.61037157077717 65 66
parm u 0 0 3.61037157077717 3.61037157077717
end
v 13.916792 16.934465 0
v 12.120592 16.95984 0
cstype bspline
deg 1
curv 0 1.796379227954109 67 68
parm u 0 0 1.796379227954109 1.796379227954109
end
v 14.4 0 0
v 14.8256 1.862 0
cstype bspline
deg 1
curv 0 1.910020774756128 69 70
parm u 0 0 1.910020774756128 1.910020774756128
end
v 4.548360000000001 21.690325 0
v 7.49796 21.844825 0
cstype bspline
deg 1
curv 0 2.953643582086368 71 72
parm u 0 0 2.953643582086368 2.953643582086368
end
v 13.35828 22.748725 0
v 16.02804 22.953925 0
cstype bspline
deg 1
curv 0 2.677634309908655 73 74
parm u 0 0 2.677634309908655 2.677634309908655
end
v 23.35828 23.998725 0
v 25.96796 24.153575 0
cstype bspline
deg 1
curv 0 2.614270113224723 75 76
parm u 0 0 2.614270113224723 2.614270113224723
end
v 31.96788 24.860725 0
v 34.1978 25.096625 0
cstype bspline
deg 1
curv 0 2.242363042952679 77 78
parm u 0 0 2.242363042952679 2.242363042952679
end
v 4.548360000000001 21.690325 0
v 2.5 22.3125 0
cstype bspline
deg 1
curv 0 2.1407663161179 79 80
parm u 0 0 2.1407663161179 2.1407663161179
end
v 7.49796 21.844825 0
v 7.5 22.9375 0
cstype bspline
deg 1
curv 0 1.092676904315727 81 82
parm u 0 0 1.092676904315727 1.092676904315727
end
v 13.35828 22.748725 0
v 12.5 23.5625 0
cstype bspline
deg 1
curv 0 1.182740169701275 83 84
parm u 0 0 1.182740169701275 1.182740169701275
end
v 16.02804 22.953925 0
v 17.5 24.1875 0
cstype bspline
deg 1
curv 0 1.920513869313367 85 86
parm u 0 0 1.920513869313367 1.920513869313367
end
v 23.35828 23.998725 0
v 22.5 24.8125 0
cstype bspline
deg 1
curv 0 1.182740169701275 87 88
parm u 0 0 1.182740169701275 1.182740169701275
end
v 25.96796 24.153575 0
v 27.5 25.4375 0
cstype bspline
deg 1
curv 0 1.998902190509829 89 90
parm u 0 0 1.998902190509829 1.998902190509829
end
v 31.96788 24.860725 0
v 32.5 26.0625 0
cstype bspline
deg 1
curv 0 1.314311547931084 91 92
parm u 0 0 1.314311547931084 1.314311547931084
end
v 34.1978 25.096625 0
v 37.5 26.6875 0
cstype bspline
deg 1
curv 0 3.665434231523598 93 94
parm u 0 0 3.665434231523598 3.665434231523598
end
v 2.5 22.3125 0
v 7.5 22.9375 0
cstype bspline
deg 1
curv 0 5.038911092686593 95 96
parm u 0 0 5.038911092686593 5.038911092686593
end
v 7.5 22.9375 0
v 12.5 23.5625 0
cstype bspline
deg 1
curv 0 5.038911092686593 97 98
parm u 0 0 5.038911092686593 5.038911092686593
end
v 22.5 24.8125 0
v 27.5 25.4375 0
cstype bspline
deg 1
curv 0 5.038911092686593 99 100
parm u 0 0 5.038911092686593 5.038911092686593
end
v 27.5 25.4375 0
v 32.5 26.0625 0
cstype bspline
deg 1
curv 0 5.038911092686593 101 102
parm u 0 0 5.038911092686593 5.038911092686593
end
v 32.5 26.0625 0
v 37.5 26.6875 0
cstype bspline
deg 1
curv 0 5.038911092686593 103 104
parm u 0 0 5.038911092686593 5.038911092686593
end
v 2.5 24.3125 0
v 2.5 22.3125 0
cstype bspline
deg 1
curv 0 2 105 106
parm u 0 0 2 2
end
v 7.5 24.9375 0
v 7.5 22.9375 0
cstype bspline
deg 1
curv 0 2 107 108
parm u 0 0 2 2
end
v 12.5 25.5625 0
v 12.5 23.5625 0
cstype bspline
deg 1
curv 0 2 109 110
parm u 0 0 2 2
end
v 22.5 26.8125 0
v 22.5 24.8125 0
cstype bspline
deg 1
curv 0 2 111 112
parm u 0 0 2 2
end
v 27.5 27.4375 0
v 27.5 25.4375 0
cstype bspline
deg 1
curv 0 2 113 114
parm u 0 0 2 2
end
v 32.5 28.0625 0
v 32.5 26.0625 0
cstype bspline
deg 1
curv 0 2 115 116
parm u 0 0 2 2
end
v 37.5 28.6875 0
v 37.5 26.6875 0
cstype bspline
deg 1
curv 0 2 117 118
parm u 0 0 2 2
end
v 40 26.6875 0
v 37.5 26.6875 0
cstype bspline
deg 1
curv 0 2.5 119 120
parm u 0 0 2.5 2.5
end