# yade-users team mailing list archive

## Re: [Question #689434]: How to generate many polyhedra randomly without specific data in Potential Blocks code？

Vasileios Angelidakis proposed the following answer:
Hi Jie,

You have actually revealed a different bug in the code; many thanks for that! I see that if size=(0.06,0.06,0.06), we do not get correct volume/centroid, due to undetected duplicate vertices in the PBs. I will go through the source code again to find a permanent fix for this. In the meanwhile, if you scale the particle e.g. with size=(0.6,0.6,0.6), like below, you get the correct volume/centroid/inertia/orientation/vertices.

All the best,
Vasileios

#####################
import numpy as np
import math
import random
#########################################################################Define physical parameters
powderDensity = 2500
young = 1e9
FricDegree1= atan(.6)
m = PolyhedraMat()
m.density = powderDensity
m.young = young
m.poisson = 0.25
m.frictionAngle = FricDegree1
#########################################################################Forming polyhedra with polyhedra function
t = polyhedra_utils.polyhedra(m,size=(0.6,0.6,0.6),seed =3) #size=(0.06,0.06,0.06)
#t.state.ori=Quaternion((1,0,0),0)
#t.state.pos = (0.,0.,0.5)
O.bodies.append(t)
########################################################################Polyhedron transformation
def dvalue(vecn1,pp1):
dd1=1*(vecn1[0]*pp1[0]+vecn1[1]*pp1[1]+vecn1[2]*pp1[2])
return dd1

chosenR=0.001
for b in O.bodies:
aa=[]
bb=[]
cc=[]
dd=[]
if not isinstance(b.shape,Polyhedra): # skip non-polyhedra bodies
continue
vs = [b.state.ori*v for v in b.shape.v] # vertices in global coords
face2=b.shape.GetSurfaces()

id1=0
while id1<len(face2):
face11=face2[id1]
if len(face11)>2:
vec1=vs[face11[2]]-vs[face11[1]]; vec1.normalize()
vec2=vs[face11[0]]-vs[face11[1]]; vec2.normalize() #Normalize this object in-place.
vects=vec1.cross(vec2); vects.normalize()

dvalue2=dvalue(vects,vs[face11[0]]) # Some dvalue2 values return equal to 0. Check this part of your script once more.
dv=dvalue2-chosenR

#			if dv<0:
#				vects=[-1*vects[0],-1*vects[1],-1*vects[2]]
#				dv=-1*dv

aa.append(vects[0])
bb.append(vects[1])
cc.append(vects[2])
dd.append(dv)

id1=id1+1

#######################################################################################
O.engines=[
ForceResetter(),
InteractionLoop(
[Ig2_PB_PB_ScGeom(twoDimension=False, unitWidth2D=1.0, calContactArea=True)],
[Ip2_FrictMat_FrictMat_KnKsPBPhys(kn_i=1e8, ks_i=1e7, Knormal=1e8, Kshear=1e7, useFaceProperties=False, viscousDamping=0.2)],
[Law2_SCG_KnKsPBPhys_KnKsPBLaw(label='law',neverErase=False, allowViscousAttraction=True, traceEnergy=False)]
),
#GlobalStiffnessTimeStepper(),
NewtonIntegrator(damping=0.0,exactAsphericalRot=True,gravity=[0,-9.81,0]),
#PotentialBlockVTKRecorder(fileName='./vtk/cubePBscaled',iterPeriod=10000,twoDimension=False,sampleX=50,sampleY=50,sampleZ=50,maxDimension=0.2,label='vtkRecorder')
]
#print(aa,bb,cc,dd)
bbb=Body()
bbb.aspherical=True
wire=False
color=[125,2,1]
highlight=True
bbb.shape=PotentialBlock(k=0.0, r=chosenR, R=0.0, a=aa, b=bb, c=cc, d=dd)
utils._commonBodySetup(bbb, bbb.shape.volume, bbb.shape.inertia,material='frictionless', pos=bbb.shape.position, fixed=False)
bbb.state.ori=bbb.shape.orientation
#bbb.state.pos = [0,0.1,0]
#bbb.shape.position+t.shape.GetCentroid()
#bbb.state.ori=Quaternion((1,0,0),0)
O.bodies.append(bbb)
###################

v=qt.View()

print("Volume")
print(t.shape.GetVolume())
print(bbb.shape.volume)

print("Centroid")
print(t.shape.GetCentroid())
print(bbb.shape.position)

print("Principal inertia tensor")
print(t.shape.GetInertia())
print(bbb.shape.inertia)

print("Principal orientations")
print(t.shape.GetOri())
print(bbb.shape.orientation)

--