# Making hair go straight up instead of following the shape?

So I'm making trees on a hill. But from what I know, trees grow straight up, and not at an angle. So how would you make the hair particles go straight up and not at an angle. Here's an example of the problem I'm having.

I would like the trees instead of going outwards, to go upwards.

How could you do this?

• Note that trees don't always go straight upwards, though it is of course by far the most usual configuration. Commented Sep 27, 2015 at 21:00
• @LightnessRacesinOrbit Thanks! I'll try to find some reference to see the angle for the trees Commented Sep 27, 2015 at 21:19

Enable Advanced and Rotation, then set the Initial Orientation to Global Z:

Note that you'll have to rotate your objects so they are facing either the +X or +Y direction instead of the +Z direction. See Why are the objects in my hair particle system not sitting on top of the ground?.

By using this technique the orientation of the particles is kept independent of their size, and you can add some random rotations via the Particle settings > Rotation > Random settings:

Adding such randomizations will help make repeated use of the same models less noticeable.

• This solution is more correct and clean. That's the way it was meant to achieve that goal. It deserves more upvotes and to be mark as accepted. Commented Sep 28, 2015 at 9:00
• I'm unsure whether to mark this one or the other one. Since the other has more upvotes I'll stick with it but if everyone prefers this question I'll mark it as correct Commented Oct 4, 2015 at 13:43
• @Chickenator The answer you mark as accepted is entirely up to you. The question isn't which answer other people prefer, it's what answer you prefer. Votes are there to show what the majority prefer, but you don't have to follow them ;) Commented Oct 4, 2015 at 18:55
• Well since your answer also showed random rotation and better ways to do it I'll mark it. Commented Oct 4, 2015 at 19:02

By enabling Advanced settings checkbox in the Hair partices system...

...you'll be able to see the Velocity panel, where the Hair emission vector's components can be defined.

By default hairs are emitted toward the face's normal.

Set the Normal value to 0 and increase the value of the wanted emitted vector axis, in your case Z.