Aligning grass blades in particles group distribution


In a nutshell: since Blender 2.59, objects in groups used with particles have global x axis aligned with the emitter surface normal.

Featured image is a detail from my current lakeside house project.

Long version: my New Year resolution to finish last years projects brought me back to an old frustrating problem: grass made from grouped objects distributed with the particles system was messed up in the latest Blender versions due to changes made in Blender after release 2.59. And I actually never understood well the particle settings mechanism so I decided to try harder. Actually it is not a fix, as nothing is really broken, just a matter of understanding what those settings actually do.

This problem came out in the Nature Academy and several people posted there about rotating the objects in the group or changing other settings but as I already had tried to change the settings by myself I had all messed up and couldn’t get my file to work. I used a few 3d grass blades from Andrew Price Nature Academy resources for this test.

So here it is, I hope well sorted out:

1. Create some grass blades (or whatever you need, like flowers or lilipads or people in a crowd) and make them a group.

2. The particle system will stick the grass in the ground with the x axis pointing up. More exactly the global x axis, the red one, so have the objects aligned as below, origin of object at base of blade, and don’t forget to apply scale just in case, otherwise you’ll get weird scaling problems:

note: Blender versions previous to 2.59 used the y global axis.

3. Check the ground object. In edit mode check the normals direction, they should be pointing up, if not use flip normals until they do. And of course.. do apply scale!

Add particle system set to hair, advanced. In render tab select the group. “Rotation” must be checked. I highlighted the main settings for adjusting size and density.

4. As a bonus and a check that all went well, you should be able to make some rotation adjustments fiddling with the highlighted settings:

In the rotation tab, Phase must not be zero so random setting to work.

If the scene moves slow you can go to the Display tab in the particles settings and let only a percent of the particles show. You can also turn the viewport visibility of the particles on and off in the outliner to the modifiers panel.
Another cool thing to do is using vertex groups and weight painting to make the particles appear just on parts of the emitter mesh but that’s a bit difficult for me to tackle in this same post.

I welcome feedback from those that have tested this so we make sure I got it right this time 😉

  • Nanette Tredoux

    Thank you so much for this, it was driving me crazy! I figured everything else except for the issue that phase must not be set to zero.

  • Oana

    Glad to help, I was bugged for a long time by this, really some Blender settings are too.. advanced..! Hope they don’t change it again 🙂

  • Carrozza

    Thank you Oana!
    These days I’m trying to realize a little garden and facing all kind of weirdness, like floating grass or horizontal blades… hope that with your hints something will start going in the right direction… UP! ^__^

  • Oana

    Oh! Floating grass? that reminded me to add one detail to the post, center point of grass blades must be set properly at the base of the blade object. Good luck with your gardening! 🙂

  • Ray Tungsteen

    I’ve come across this problem myself… It’s a funny one for sure! And wasn’t it changed again in 2.60? I might be wrong about that. But at some point recently, either 2.59 or 2.60, it was changed so that you no longer had to rotate the object but you can now alter the alignment axis in the Relations Extra part of the Object panel (which was previously called something else, like “Animation Tricks” or something, I forget). This is just a touch faster than rotating the object, so it’s worth trying.

    BTW, I stopped blogging because I don’t really have the time. But I might do something else with the website later, will see how things go.

  • Oana

    I didn’t even notice that setting, thanks Ray!

  • John

    Thank you so much! This was driving me crazy too. The key finding for me was that the X (red) axis will be pointing up. I rotated my grass around and it works perfectly. Thanks!!

  • I didn’t use the particle object group feature for a while only to find the landscapes I made in de early 2.5 days ruined when trying to reuse them in a 2.65-project. I lost a couple of hours trying to fix it, with no result. You saved my day with your explanation of the X-axis orientation. Thanks a lot Oana!

    @ray I tried the relations-setting. Didn’t work for me.

  • Oana

    Cool 🙂

  • JohnV

    Hi Oana! Very helpful information! I was wondering if object distribution using particle system can be achieved with a grayscale density image. Could I use that kind of image as reference for the density of the object spreading over a subdivided plane?

    To help you understand better what I am trying to achieve, I import a heightmap in blender, 1024×1024 vertices, and I want to spread trees over it. But I don’t want the density to be the same all over the terrain. I need parts free of trees, like the rocky ones. I have a 1024×1024 pixel grayscale image, which indicates those parts where trees should be applied (the more white a pixel is, the most likely for a tree to appear, the more black it it is, the less likely). So, what would you suggest me to do?

  • Darrick Roberts

    Thank you very much!

  • Ppl like you get all the brasni. I just get to say thanks for he answer.

  • Wow! This blog looks just like my old one! It’s on a completely different topic but it has pretty much the same page layout and design. Wonderful
    choice of colors!

    My web site: home sealing

  • obviously like your web site but you have to
    test the spelling on quite a few of your posts. Several of them are rife with spelling problems
    and I to find it very bothersome to tell the reality then again I’ll certainly come
    back again.

  • Hello it’s me, I am also visiting this web site daily,
    this website is truly fastidious and the viewers are really sharing good thoughts.

  • Hi, after reading this awesome piece of writing i am as well
    happy to share my know-how here with colleagues.