# Microstructure Mesh Process¶

## Python Script¶

The basename for this file is `docs_banner.py`

.
The file can be run using this command:

```
microstructpy --demo=docs_banner.py
```

The full text of the file is:

```
from __future__ import division
import os
import numpy as np
import scipy.stats
from matplotlib import pyplot as plt
import microstructpy as msp
def main():
# Colors
c1 = '#12C2E9'
c2 = '#C471ED'
c3 = '#F64F59'
# Offset
off = 1
# Create Directory
dirname = os.path.join(os.path.dirname(__file__), 'docs_banner')
if not os.path.exists(dirname):
os.makedirs(dirname)
# Create Domain
domain = msp.geometry.Rectangle(width=10, length=20)
# Create Unpositioned Seeds
phase2 = {'color': c1}
ell_geom = msp.geometry.Ellipse(a=8, b=3)
ell_seed = msp.seeding.Seed(ell_geom, phase=2)
mu = 1
bnd = 0.5
d_dist = scipy.stats.uniform(loc=mu-bnd, scale=2*bnd)
phase0 = {'color': c2, 'shape': 'circle', 'd': d_dist}
phase1 = {'color': c3, 'shape': 'circle', 'd': d_dist}
circle_area = domain.area - ell_geom.area
seeds = msp.seeding.SeedList.from_info([phase0, phase1], circle_area)
seeds.append(ell_seed)
hold = [False for seed in seeds]
hold[-1] = True
phases = [phase0, phase1, phase2]
# Create Positioned Seeds
seeds.position(domain, hold=hold, verbose=True)
# Create Polygonal Mesh
pmesh = msp.meshing.PolyMesh.from_seeds(seeds, domain)
# Create Triangular Mesh
tmesh = msp.meshing.TriMesh.from_polymesh(pmesh,
min_angle=12,
max_edge_length=0.2,
max_volume=0.4)
# Create Figure
k = 0.12
len_x = 3 * domain.length + 4 * off
len_y = domain.width + 2 * off
plt.figure(figsize=(k * len_x, k * len_y))
# Plot Seeds
seed_colors = [phases[s.phase]['color'] for s in seeds]
seeds.plot(color=seed_colors, alpha=0.8, edgecolor='k', linewidth=0.3)
domain.plot(facecolor='none', edgecolor='k', linewidth=0.3)
# Plot Polygonal Mesh
pmesh.points = np.array(pmesh.points)
pmesh.points[:, 0] += domain.length + off
for region, phase_num in zip(pmesh.regions, pmesh.phase_numbers):
if phase_num == 2:
continue
color = phases[phase_num]['color']
facets = [pmesh.facets[f] for f in region]
kps = ordered_kps(facets)
x, y = zip(*[pmesh.points[kp] for kp in kps])
plt.fill(x, y, color=color, alpha=0.8, edgecolor='none')
ellipse_regions = set()
for region_num, phase_num in enumerate(pmesh.phase_numbers):
if phase_num == 2:
ellipse_regions.add(region_num)
ellipse_facets = []
for facet, neighbors in zip(pmesh.facets, pmesh.facet_neighbors):
common_regions = ellipse_regions & set(neighbors)
if len(common_regions) == 1:
ellipse_facets.append(facet)
ellipse_kps = ordered_kps(ellipse_facets)
x, y = zip(*[pmesh.points[kp] for kp in ellipse_kps])
plt.fill(x, y, color=phases[-1]['color'], alpha=0.8, edgecolor='none')
for facet, neighbors in zip(pmesh.facets, pmesh.facet_neighbors):
common_regions = ellipse_regions & set(neighbors)
if len(common_regions) < 2:
x, y = zip(*[pmesh.points[kp] for kp in facet])
plt.plot(x, y, color='k', linewidth=0.3)
# Plot Triangular Mesh
tmesh.points = np.array(tmesh.points)
tmesh.points[:, 0] += 2 * off + 2 * domain.length
tri_colors = [seed_colors[n] for n in tmesh.element_attributes]
tmesh.plot(color=tri_colors, alpha=0.8, edgecolor='k', linewidth=0.2)
# Set Up Axes
plt.gca().set_position([0, 0, 1, 1])
plt.axis('image')
plt.gca().set_axis_off()
plt.gca().get_xaxis().set_visible(False)
plt.gca().get_yaxis().set_visible(False)
xlim, ylim = domain.limits
xlim[0] -= off
xlim[1] += 3 * off + 2 * domain.length
ylim[0] -= off
ylim[1] += off
plt.axis(list(xlim) + list(ylim))
fname = os.path.join(dirname, 'banner.png')
plt.savefig(fname, bbox='tight', pad_inches=0)
plt.savefig(fname.replace('.png', '.pdf'), bbox='tight', pad_inches=0)
def ordered_kps(pairs):
t_pairs = [tuple(p) for p in pairs]
kps = list(t_pairs.pop())
while t_pairs:
for i, pair in enumerate(t_pairs):
if kps[-1] in pair:
break
assert kps[-1] in pair, pairs
kps += [kp for kp in t_pairs.pop(i) if kp != kps[-1]]
return kps[:-1]
if __name__ == '__main__':
main()
```

## Domain Geometry¶

The materials fill a rectangular domain with side lengths 20 and 10. The center of the rectangle defaults to the origin.

## Seeds¶

The first material is phase 2, which contains a single elliptical seed with semi-axes 8 and 3. Next, phases 0 and 1 are created with identical size distributions and different colors. The size distributions are uniform random from 0.5 to 1.5. Seeds of phase 0 and phase 1 are generated to fill the area between the rectangular domain and the elliptical seed from phase 2.

Next, the phase 2 seed is appended to the list of phase 0 and 1 seeds.
A hold list is then created to indicate to
`position()`

which seeds should have their positions (centers) held.
The default position of a seed is the origin, so by setting the hold flag to
`True`

for the elliptical seed, it will be fixed to the center of the domain
while the remaining seeds will be randomly positioned around it.

## Polygonal and Triangular Meshing¶

Once the seeds are positioned in the domain, a polygonal mesh is created using
`from_seeds()`

.
The triangular mesh is created using
`from_polymesh()`

,
with the quality control settings `min_angle`

, `max_edge_length`

, and
`max_volume`

.

## Plot Figure¶

The figure contains three plots: the seeds, the polygonal mesh, and the
triangular/unstructured mesh.
First, the seeds plot is generated using SeedList
`plot()`

and Rectangle
`plot()`

to show the boundary of the domain.
The seeds are plotted with some transparency to show overlap.

Next, the polygonal mesh is translated to the right and plotted in such a way that avoids the internal geometry of the elliptical seed. This internal geometry is created by the multi-circle approximation used in polygonal meshing, then removed during the triangular meshing process. In the interest of clarity, these two steps are combined and the elliptical grain is plotted without internal geomtry.

Finally, the triangular mesh is translated to the right of the polygonal mesh
and plotted using TriMesh
`plot()`

.

Once all three plots have been added to the figure, the axes and
aspect ratio are adjusted.
This figure is shown in Fig. 27.
The PNG and PDF versions of this plot are saved in a folder named
`docs_banner`

, in the current directory (i.e `./docs_banner`

).

The three major steps are: 1) seed the domain with particles, 2) create a Voronoi power diagram, and 3) convert the diagram into an unstructured mesh.