def generate_offset_track(self, mid_track, thickness):
poly_line = LinearRing(mid_track)
poly_line_offset_left = poly_line.parallel_offset(thickness,
side="left",
resolution=16,
join_style=2,
mitre_limit=2)
poly_line_offset_right = poly_line.parallel_offset(thickness,
side="right",
resolution=16,
join_style=2,
mitre_limit=2)
offset_left_track = []
for coord in poly_line_offset_left.coords:
p = [coord[0], coord[1]]
offset_left_track.append(p)
offset_left_track.append(offset_left_track[0])
offset_right_track = []
for coord in poly_line_offset_right.coords:
p = [coord[0], coord[1]]
offset_right_track.append(p)
offset_right_track.append(offset_right_track[0])
return offset_left_track, offset_right_track
def offset_perimeter(geometry, offset, side='left', plot_offset=False):
"""Offsets the perimeter of a geometry of a :class:`~sectionproperties.pre.sections.Geometry`
object by a certain distance. Note that the perimeter facet list must be entered in a
consecutive order.
:param geometry: Cross-section geometry object
:type geometry: :class:`~sectionproperties.pre.sections.Geometry`
:param float offset: Offset distance for the perimeter
:param string side: Side of the perimeter offset, either 'left' or 'right'. E.g. 'left' for a
counter-clockwise offsets the perimeter inwards.
:param bool plot_offset: If set to True, generates a plot comparing the old and new geometry
The following example 'corrodes' a 200UB25 I-section by 1.5 mm and compares a few of the
section properties::
import sectionproperties.pre.sections as sections
from sectionproperties.pre.offset import offset_perimeter
from sectionproperties.analysis.cross_section import CrossSection
# calculate original section properties
original_geometry = sections.ISection(d=203, b=133, t_f=7.8, t_w=5.8, r=8.9, n_r=16)
original_mesh = original_geometry.create_mesh(mesh_sizes=[3.0])
original_section = CrossSection(original_geometry, original_mesh)
original_section.calculate_geometric_properties()
original_area = original_section.get_area()
(original_ixx, _, _) = original_section.get_ic()
# calculate corroded section properties
corroded_geometry = offset_perimeter(original_geometry, 1.5, plot_offset=True)
corroded_mesh = corroded_geometry.create_mesh(mesh_sizes=[3.0])
corroded_section = CrossSection(corroded_geometry, corroded_mesh)
corroded_section.calculate_geometric_properties()
corroded_area = corroded_section.get_area()
(corroded_ixx, _, _) = corroded_section.get_ic()
# compare section properties
print("Area reduction = {0:.2f}%".format(
100 * (original_area - corroded_area) / original_area))
print("Ixx reduction = {0:.2f}%".format(
100 *(original_ixx - corroded_ixx) / original_ixx))
The following plot is generated by the above example:
.. figure:: ../images/offset_example.png
:align: center
:scale: 75 %
200UB25 with 1.5 mm corrosion.
The following is printed to the terminal:
.. code-block:: text
Area reduction = 41.97%
Ixx reduction = 39.20%
"""
# initialise perimeter points list
perimeter_points = []
# add perimeter points to the list
for facet_idx in geometry.perimeter:
# get the facet
facet = geometry.facets[facet_idx]
# get the first point on the facet
point = geometry.points[facet[0]]
# add the (x,y) tuple to the list
perimeter_points.append((point[0], point[1]))
# create LinearRing object
perimeter = LinearRing(perimeter_points)
# offset perimeter
new_perimeter = perimeter.parallel_offset(distance=offset,
side=side,
resolution=0,
join_style=2)
(new_xcoords, new_ycoords) = new_perimeter.xy
# create deep copy of original geometry object
new_geometry = copy.deepcopy(geometry)
# replace offset points in new geometry
for (i, facet_idx) in enumerate(new_geometry.perimeter):
# get the facet
facet = new_geometry.facets[facet_idx]
# get the first point on the facet
point = new_geometry.points[facet[0]]
# replace the point location with the offset location
point[0] = new_xcoords[i]
point[1] = new_ycoords[i]
if plot_offset:
(_, ax) = plt.subplots()
# plot new geometry
for (i, f) in enumerate(new_geometry.facets):
if i == 0:
ax.plot([
new_geometry.points[f[0]][0], new_geometry.points[f[1]][0]
], [
new_geometry.points[f[0]][1], new_geometry.points[f[1]][1]
],
'ko-',
markersize=2,
label='Offset Geometry')
else:
ax.plot([
new_geometry.points[f[0]][0], new_geometry.points[f[1]][0]
], [
new_geometry.points[f[0]][1], new_geometry.points[f[1]][1]
],
'ko-',
markersize=2)
# plot the original perimeter
for (i, facet_idx) in enumerate(geometry.perimeter):
f = geometry.facets[facet_idx]
if i == 0:
ax.plot([geometry.points[f[0]][0], geometry.points[f[1]][0]],
[geometry.points[f[0]][1], geometry.points[f[1]][1]],
'r--',
markersize=2,
label='Original Perimeter')
else:
ax.plot([geometry.points[f[0]][0], geometry.points[f[1]][0]],
[geometry.points[f[0]][1], geometry.points[f[1]][1]],
'r--',
markersize=2)
ax.legend(loc='center left', bbox_to_anchor=(1, 0.5))
ax.set_title('Offset Geometry')
ax.set_aspect('equal', anchor='C')
plt.tight_layout()
plt.show()
return new_geometry
