Script to render one object from different angles

Question

I'm new to Blender. I'm currently working on a 3D reconstruction project using neural networks. I need to create my data set. Therefore I need to render a 3D body scan from different angles and save the images separately. I can render creating cameras manually but once i create a loop for the cameras my output is black images. this is the code i used:

bpy.ops.object.camera_add(view_align=False, location=[0,10,20], rotation=[0.436,0,pi])
bpy.ops.object.camera_add(view_align=False, location=[10,20,30], rotation=[0.436,0,pi])



for ob in scene.objects:
    if ob.type == 'CAMERA':
        bpy.context.scene.camera = ob
        print('Set camera %s' % ob.name )
        file = os.path.join('/home/fotofinder/Downloads/tryrender/images', ob.name )
        bpy.context.scene.render.filepath = file
        bpy.ops.render.render( write_still=True ) 

If anyone can help to define the proper parameters for the cameras in order to always have the object in the image I would be grateful.

Answer 1

import bpy
from math import *
from mathutils import *

#set your own target here
target = bpy.data.objects['Cube']
cam = bpy.data.objects['Camera']
t_loc_x = target.location.x
t_loc_y = target.location.y
cam_loc_x = cam.location.x
cam_loc_y = cam.location.y

#dist = sqrt((t_loc_x-cam_loc_x)**2+(t_loc_y-cam_loc_y)**2)
dist = (target.location.xy-cam.location.xy).length
#ugly fix to get the initial angle right
init_angle  = (1-2*bool((cam_loc_y-t_loc_y)<0))*acos((cam_loc_x-t_loc_x)/dist)-2*pi*bool((cam_loc_y-t_loc_y)<0)

num_steps = 36 #how many rotation steps
for x in range(num_steps):
    alpha = init_angle + (x+1)*2*pi/num_steps
    cam.rotation_euler[2] = pi/2+alpha
    cam.location.x = t_loc_x+cos(alpha)*dist
    cam.location.y = t_loc_y+sin(alpha)*dist
    file = os.path.join('/home/fotofinder/Downloads/tryrender/images', x)
    bpy.context.scene.render.filepath = file
    bpy.ops.render.render( write_still=True ) 

Old answer

I created a new blendfile (with the default cube) changed the render engine to cycles and changed the code as follows:

#Run with "blender -b TARGET.blend -P thisfile.py 

#Added imports 
import bpy
from mathutils import *
from math import *
import os
scene = bpy.context.scene

bpy.ops.object.camera_add(view_align=False, location=[0,10,20], rotation=[0.436,0,pi])
bpy.ops.object.camera_add(view_align=False, location=[10,20,30], rotation=[0.436,0,pi])



for ob in scene.objects:
    if ob.type == 'CAMERA':
        bpy.context.scene.camera = ob
        print('Set camera %s' % ob.name )
        file = os.path.join('/home/fotofinder/Downloads/tryrender/images', ob.name )
        bpy.context.scene.render.filepath = file
        bpy.ops.render.render( write_still=True ) 

results were as expected:

Camera.001.png: [] Camera.002.png: Camera.png:

So even if it's not pretty, your script works. I would assume your background is black, and the cameras a missaligned

Some people say it is important to avoid bpy.ops commands. I would assume the best practice for creating new cameras would be

cam = bpy.data.cameras.new("Camera")
cam_ob = bpy.data.objects.new("Camera", cam)
bpy.context.collection.objects.link(cam_ob)
#To set location and rotation: 
cam_ob.location = (6,26,14)
cam_ob.rotation_euler = Euler((62.0*pi/180, 0.0*pi/180, 167*pi/180)

Answer 2

Could you take an approach something like this?

• Create a mesh whose vertices are the desired viewpoint positions, around your body scan. (It's the sphere, in the illustration, named 'Viewpoints')
• Create one camera, and assign it a 'Track To' constraint ('To': -Z, 'Up': Y) with the body scan as target

Run a script which keyframes the camera to each of the vertex locations in successive frames

import bpy

vp_obj = bpy.data.objects['Viewpoints']
cam_obj = bpy.data.objects['Camera']
vp_vs = vp_obj.data.vertices

bpy.context.scene.frame_start=1
bpy.context.scene.frame_end=len(vp_vs)

for (f,v) in enumerate(vp_vs,1):
    cam_obj.location = vp_obj.matrix_world * v.co
    cam_obj.keyframe_insert(data_path="location", frame=f)

.. and render the animation?

Answer 3

Make a dolly

There are already a number of answers re rendering from different angles.

How to automatically render from several camera angles?

Here is take that sets up an empty on your object as a dolly. A camera is parented to the empty, such that when the empty has no rotation the camera is a front view.

Adjusting the empties rotaion x and z is equivalent of latitude and longitude.

Here is a helper script to add the empty camera setup in 2.80

import bpy
from math import radians
context = bpy.context

bpy.ops.object.empty_add(location=(0, 0, 0))
mt = context.object
mt.empty_display_type = 'ARROWS'
mt.empty_display_size = 4
bpy.ops.object.camera_add(location=(0, -1, 0))
cam = context.object
cam.rotation_euler = (radians(90), 0, radians(0))
cam.parent = mt
cam.data.type = 'ORTHO'
context.scene.camera = cam

I have made the camera ORTHO to take advantage of method outlined here

Check if the whole plane is being on a orthographic camera render (or get a proportion of the rendered plane) to scale the camera to fit mesh.

final result of running script below, after setting up camera above, whoops notice 45 lat is south, needs a minor fix 8^). The camera is scaled such that the whole object fits

Test script. Select object to render. I have hardcoded in two latitude longitude pairs, (0, 0) and (45, 45).

import bpy
from mathutils import Vector
from math import radians
context = bpy.context
dg = context.evaluated_depsgraph_get()
scene = context.scene
# add empty
cam_ob = scene.camera
# make sure run other script first to give cam parent empty
mt = cam_ob.parent

plane = context.object
mt.parent = plane

pmw = plane.matrix_world
bbox = [Vector(b) for b in plane.bound_box]
plane_co = sum(bbox, Vector()) / 8
cam_ob.location.y = (pmw @ bbox[0]).length

coords = [t for b in plane.bound_box for t in pmw @ Vector(b)]

for lat, lon in ((0, 0),(45, 45)):
    mt.rotation_euler = (radians(lat), 0, radians(lon))
    dg.update()
    v, scale = cam_ob.camera_fit_coords(dg, coords)

    cam_ob.data.ortho_scale = scale
    cam_ob.matrix_world.translation = v
    # render

Now we only need to input the latitude and longitude of the camera.

• Assumes the object's origin is centre of bounding box. The script sets the object as the parent of the camera "dolly" empty.

• If you are using 2.79 or prior, replace any occurence of @ with * and context.depsgraph with context.scene