How do i get hair positions from a hair particle system?

Question

I'm trying to get the positions of the hair vertices and looked at how some plugins do it. It's usually something like this, using the co_hair function:

import bpy

obj=bpy.context.active_object
ps = obj.particle_systems[0]
strands = len(ps.particles)
if ps.settings.child_type == 'NONE': 
    start_id, count = (0, strands)
else:
    start_id, count = (strands, len(ps.child_particles))
 
length = 2 ** ps.settings.display_step + 1
for particle_idx in range(start_id, start_id + count):
    for step in range(length):
        e = ps.co_hair(obj, particle_no=particle_idx, step=step)
        print(e)

Yet when i try this, i only get empty vectors:

<Vector (0.0000, 0.0000, 0.0000)>
<Vector (0.0000, 0.0000, 0.0000)>
...

What am i doing wrong?

Answer 1

If you just need the position of hair data, you should use particles instead of co_hair:

import bpy

for particle in bpy.context.active_object.particle_systems[0].particles:
    print(particle.location)
    # to access each segments
    #for fiber_point in particle.hair_keys:
    #    print(fiber_point.co_local)

Noted that co_local is in its local coordinate system, relative to the emitting face.

co_hair is for cache hair data. It maybe relates to the cache system of Hair Dynamics.