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I am using the particle system to spawn thousands of grass objects which are just planes (imagine 10cm tall, 2m wide) with texture mapped on them. How do I get the planes to follow the ground (rest on ground) while also being vertical. There are questions about hairs but not about this specific issue.

Like this: https://i.imgur.com/0PryYku.png

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    $\begingroup$ maybe you need to enable the Advanced option, then enable Rotation and in Rotation > Initial Orientation choose Global Z, as explained here: blender.stackexchange.com/questions/39192/… $\endgroup$ – moonboots Aug 31 '18 at 8:51
  • $\begingroup$ Thanks for the comment. However the problem is not to get the grass to point upwards but to make it point upwards while also following the ground. I understand particle system may not be able to do it so maybe there is another way. $\endgroup$ – Life Aug 31 '18 at 22:52
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    $\begingroup$ well I think that what I linked explain how it follows the ground, no? $\endgroup$ – moonboots Sep 1 '18 at 7:43
  • $\begingroup$ Maybe I am explaining myself poorly. I changed the image hopefully to make clear what I want. Please have a look at the image once more, thank you. $\endgroup$ – Life Sep 2 '18 at 3:40
  • $\begingroup$ oh ok sorry I understand, I don't know if it's possible $\endgroup$ – moonboots Sep 2 '18 at 4:52
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The particle system uses the normals from the mesh to grow the 'hair'. So, if you want to make all the particles grow upright and follow the terrain, what you should do is:

  1. Create another mesh above the terrain (as simple as possible, like a plane, or circle)
  2. Subdivide it a few times
  3. Use a Shrinkwrap Modifier on the new mesh, so it follows the terrain, at the same time preserves the normals pointing upwards
  4. You may use Wrap Method as Nearest surface point and Above Surface, but you may try other methods if you like
  5. Make the particle system on this new mesh; (on the modifiers list, the Shrinkwrap must be above the particle system).

This way your grass will grow upwards, and the roots will follow the terrain.

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