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160 Chapter 11: Space Warps and Particle Systems
Tip:
The b est way to view the results is from the
Top v i e w p or t .
The particles follow the path fairly closely, but
diverge noticeably at the end of the path, where
the tur ns are tightest. Correcting divergence
in t ight turns typically requires an increase in
the acceleration limit.
The particle stream diverges from the path at its
endpoint.
10. Stop at frame 100.
This wil l let you see the results of chang ing the
Speed By Icon parameters as you make the
changes.
11. OpentheModifypanel,and,ifnecessary,select
the Speed By I con operator icon.
The operator parameters appear on the Modify
panel. This is the case with any action that
uses a unique icon, and lets you adjust the
parameters without using Particle View.
12. On the Parameters rollout, use the Accel Limit
spinner to slow ly increase the value as you
observe the changes to the p article path.
As you approach a value of 150, the end of the
particle path comes closer and closer to the
Helix. You shouldn’t see much change above
150.
The endpoints now coincide.
13. Drag the time slider again.
The particle path remains similar to that of the
Helix for the entire duration of the animation.
With other setups, you mig ht need to use
different values for Influence %, and for paths
w ith tight tw ists and turns, you might need to
increase Accel Limit as well.
Youmightbewonderingwhyyoudidn’tsimply
replace the default Speed operator with the
Speed By Icon operator. To see why not, t ry this:
14. Go to frame 100, open Particle View, and click
the Speed 01 operator’s icon to turn it off. Play
the a nimation.
TheentireparticlepathisoffsetfromtheHelix,
so it’s difficult to tell how closely it follows the
latter’s curves.
15. Try adjusting the Speed By Icon’s Accel Lim it
and Influence % setting to get the particles to
follow the helical path more closely.
It’s not easy. You get more reliable results using
the Speed operator to set the initial speed, and
then Speed By Icon to set the part icle path.
To use t he U se I con Or i ent at i on opt i on:
The U se Icon Orientation option applies arc-like
motion to the particles based on rotation
animation of the icon. To best understand how
it works, it’s necessary to isolate its influence by
eliminating any potentially conflicting factors.