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I am trying to use python scripts on blender4.0 to do the following: detect whether the ray from the camera shooting point intersects with the obstacle, and find the global coordinates of the intersection point.

enter image description here

The key function ray_cast(), I can't find the official instructions, but it does work for now.

enter image description here

However, I encountered the following problems. When I changed the position of the obstacle (monkey head), I checked to see if the same ray was still blocked, only to find that the intersection position results were the same as the last time. Whether I use G to change the position or use a script to change the position, this problem occurs.

import bpy
import os

# Get the camera, target object, and obstacle object in the scene
camera = bpy.data.objects['Camera']
target_object = bpy.data.objects['Cube']
obstacle = bpy.data.objects['monkey']

# Define the ray origin and ray direction
ray_origin = camera.location
ray_direction = (target_object.location - camera.location).normalized()

output_directory = "F:/"
output_filename = "output.txt"
output_filepath = os.path.join(output_directory, output_filename)

for frame in range(5):
    obstacle.location.z += 0.5
    obstacle.update_from_editmode()
    
    obstacle.update_from_editmode()
    
    hit, location, normal, index = obstacle.ray_cast(ray_origin, ray_direction)
    
    if hit:
        output_file.write("Frame " + str(frame+1) + ": Ray intersects with the obstacle object at location: " + str(location) + "\n")
        output_file.write(output_file.write("Frame " + str(frame+1) + ": Normal at the intersection point: " + str(normal) + "\n"))
    else:
        output_file.write("Frame " + str(frame+1) + ": Ray does not intersect with the obstacle object\n")

output_file.close()

Running result enter image description here

I couldn't figure out what the problem was.

I also tried to keep the original relative position and press A to select all the objects and move them all together, which also resulted in an error (hit value changed to False).

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  • $\begingroup$ this script doesn't work. -> hit is not defined. Pls post a script which runs and which you tried out. thank you. $\endgroup$ Commented Mar 4, 2024 at 8:56
  • $\begingroup$ and even better: provide blend file, so we don't have to guess where your objects are. thx. $\endgroup$ Commented Mar 4, 2024 at 9:04
  • $\begingroup$ and yes, the code as is (if you have the ray_cast command not in the loop) will have the result you have. Since you didn't show us your "real" code, we have no idea where you placed your ray_cast command $\endgroup$ Commented Mar 4, 2024 at 9:05
  • $\begingroup$ Sorry, I re-edited the complete code, please help me to see if there is any problem. $\endgroup$ Commented Mar 5, 2024 at 2:01

1 Answer 1

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The docs for ray_cast are here.

Note that the origin and direction are given in object space. So you need to convert back and forth between world and object space.

# Location in world space
target_world = target_object.matrix_world.to_translation()
origin_world = camera_object.matrix_world.to_translation()

# Location in obstacle space
world2obj = obstacle.matrix_world.inverted()
target_obj = world2obj @ target_world
origin_obj = world2obj @ origin_world

# Direction in obstacle space
direction_obj = (target_obj - origin_obj).normalized()

# Ray cast
hit, loc_obj, normal, index = obstacle.ray_cast(origin_obj, direction_obj)

# Convert obstacle-space intersection to world space
loc_world = obstacle.matrix_world @ loc_obj
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  • $\begingroup$ Thank you so much for your help, it really worked! $\endgroup$ Commented Mar 5, 2024 at 8:35

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