Blender example: Creating a scene with 2D DIC

This example takes you through creating a scene and adding all the necessary objects required to represent a 2D DIC setup (camera, lighting and sample). This example will then show you how to render a single image of this scene.

Test case: mechanical analysis of a plate with a hole loaded in tension.

import numpy as np
from scipy.spatial.transform import Rotation
from pathlib import Path
import pyvale
import mooseherder as mh

Here we load in a pre-generated MOOSE finite element simulation dataset that comes packaged with pyvale. The simulation is purely mechanical test case in

3D of a plate with a hole loaded in tension. A mentioned in previous examples,

this path can be replaced with your own MOOSE simulation output in exodus format (*.e). mooseherder is then used to convert the simulation output into a SimData object.

data_path = pyvale.DataSet.render_mechanical_3d_path()
sim_data = mh.ExodusReader(data_path).read_all_sim_data()

# This is then scaled to mm, as all lengths in Blender are to be set in mm.
# The `SimData` object is then converted into a `RenderMeshData` object, as
# this skins the mesh ready to be imported into Blender.
# The `disp_comps` are the expected direction of displacement. Since this is a
# 3D deformation test case, displacement is expected in the x, y and z directions.
disp_comps = ("disp_x","disp_y", "disp_z")
sim_data = pyvale.scale_length_units(scale=1000.0,
                                     sim_data=sim_data,
                                     disp_comps=disp_comps)

render_mesh = pyvale.create_render_mesh(sim_data,
                                        ("disp_y","disp_x"),
                                        sim_spat_dim=3,
                                        field_disp_keys=disp_comps)

Firstly, a save path must be set. In order to do this a base path must be set. Then all the generated files will be saved to a subfolder within this specified base directory (e.g. blenderimages). If no base directory is specified, it will be set as your home directory.

base_dir = Path.cwd()

Creating the scene

In order to create a DIC setup in Blender, first a scene must be created. A scene is a holding space for all of your objects (e.g. camera(s), light(s) and sample(s)). A scene is initialised using the BlenderScene class. All the subsequent objects and actions necessary are then methods of this class.

scene = pyvale.BlenderScene()

The next thing that can be added to the scene is a sample. This is done by passing in the RenderMeshData object. It should be noted that the mesh will be centred on the origin to allow for the cameras to be centred on the mesh. Once the part is added to the Blender scene, it can be both moved and rotated.

part = scene.add_part(render_mesh, sim_spat_dim=3)
# Set the part location
part_location = np.array([0, 0, 0])
pyvale.BlenderTools.move_blender_obj(part=part, pos_world=part_location)
# Set part rotation
part_rotation = Rotation.from_euler("xyz", [0, 0, 0], degrees=True)
pyvale.BlenderTools.rotate_blender_obj(part=part, rot_world=part_rotation)

A camera can then be added to the scene. To initialise a camera, the camera parameters must be specified using the CameraData dataclass. Note that all lengths / distances inputted are in mm. This camera can then be added to the Blender scene. The camera can also be moved and rotated.

cam_data = pyvale.CameraData(pixels_num=np.array([1540, 1040]),
                            pixels_size=np.array([0.00345, 0.00345]),
                            pos_world=(0, 0, 400),
                            rot_world=Rotation.from_euler("xyz", [0, 0, 0]),
                            roi_cent_world=(0, 0, 0),
                            focal_length=15.0)
camera = scene.add_camera(cam_data)
camera.location = (0, 0, 410)
camera.rotation_euler = (0, 0, 0) # NOTE: The default is an XYZ Euler angle

A light can the be added to the scene. Blender offers different light types: Point, Sun, Spot and Area. The light can also be moved and rotated like the camera.

light_data = pyvale.BlenderLightData(type=pyvale.BlenderLightType.POINT,
                                     pos_world=(0, 0, 400),
                                     rot_world=Rotation.from_euler("xyz",
                                                                   [0, 0, 0]),
                                     energy=1)
light = scene.add_light(light_data)
light.location = (0, 0, 410)
light.rotation_euler = (0, 0, 0)

A speckle pattern can then be applied to the sample.

Firstly, the material properties of the sample must be specified, but these will all be defaulted if no inputs are provided.

The speckle pattern can then be specified by providing a path to an image file

with the pattern. The mm/px resolution of the camera must also be specified in order to correctly scale the speckle pattern. It should be noted that for a bigger camera or sample you may need to generate a larger speckle pattern.

material_data = pyvale.BlenderMaterialData()
speckle_path = pyvale.DataSet.dic_pattern_5mpx_path()

mm_px_resolution = pyvale.CameraTools.calculate_mm_px_resolution(cam_data)
scene.add_speckle(part=part,
                  speckle_path=speckle_path,
                  mat_data=material_data,
                  mm_px_resolution=mm_px_resolution)

Rendering an image

Once all the objects have been added to the scene, an image can be rendered. Firstly, all the rendering parameters must be set, including parameters such as the number of threads to use.

render_data = pyvale.RenderData(cam_data=cam_data,
                                base_dir=base_dir,
                                threads=8)

A single image of the scene can then be rendered. If stage_image is set to True, the image will be saved to disk, converted to an array, deleted and the image array will be returned. This is due to the fact that an image cannot be saved directly as an array through Blender.

scene.render_single_image(stage_image=False,
                          render_data=render_data)

The rendered image will be saved to this filepath:

print("Save directory of the image:", (render_data.base_dir / "blenderimages"))

There is also the option to save the scene as a Blender project file. This file can be opened with the Blender GUI to view the scene.

pyvale.BlenderTools.save_blender_file(base_dir)