#SL Pathfinding News Wk16

We have lots of new information on Pathfinding.

This week saw the first Second Life® PUG meeting: Pathfinding User Group. This is a group lead by Falcon and Lorca Linden. It is to be held each week in PATHTEST1, ADITI. The meeting starts at 4 PM SLT/PDT. All those interested in Pathfinding are welcome.

First PUG Meeting

There is no in-world Pathfinding group for chat and drama. The meeting is not yet listed on the User Group page.


#1 – Default Character Height

Because of limitations in the underlying AI system, it’s only possible to guarantee robust Pathfinding results for a single height of character. Most of the time it doesn’t matter if your character is shorter or a bit taller, but you’ll get two artifacts.

  1. A short character may not take the most optimal path.
  2. A tall character may think it can walk somewhere but bump into a low ceiling.

Lorca Linden says the Lab will have to pick a height setting for the default Navmeshes. Falcon Linden says initially they’ll select a fixed height. But later they may allow estate owners to change it. The reason is the Lab wants as much inter-region compatibility as possible on initial release.

Character height can change. The initial fixed height is for the Navmesh. The Navmesh height is used by the Havok physics engine to calculate paths. It needs to know character height to do that. However, since we can set our character’s height and the Lindens have no idea whether we will make lots of  10cm high rats or 3 meter (9ft) Lycans they have no idea what value to use for the default. If you have a preference, now would be a good time for you to get involved.

Falcon Linden has given estate managers a new console command: set nav_mesh_height <x>. The region must be restarted for it to take effect.

You’ve probably figured out that Navmesh height will be irrelevant in outdoor areas.

If you are not building Pathfinding characters, don’t both adding an opinion. Only opinions listing an example in use on a test region will count. They are interested in the opinions of those using the features, not what people think they may want.

If you are interested in having your region run on the Pathfinding Beta Code, contact Lorca Linden.

#2 Walkability Materials

When building a Navmesh and preparing a region for Pathfinding each walkable linkset and each material volume can be set to have four Walkability values. Those values affect to each of the four LSL CHARACTER_TYPE’s; CHARACTER_TYPE_A, CHARACTER_TYPE_B, CHARACTER_TYPE_C, and CHARACTER_TYPE_D.

The Lindens are looking to assign best practices categories the four types. Possibly; TYPE_A = pathfinding vehicles, TYPE_B = pathfinding robots,  TYPE_C = animals, and TYPE_D = everything else  or possibly; quadruped, biped, and vehicle. The idea is to have some general standard for some measure of cross region compatibility.

The Lindens have no idea what range of things we may think up. So, again if you are building and experimenting with Pathfinding characters, now is a good time to supply categories to meet your needs.


In a week or so Falcon and Lorca will place a JIRA’s in PATHBUG to receive feedback.

Remember. They will be looking to see if your region has the critters before they consider your feedback.


Download the Pathfinding Project Viewer.

Wiki Pathfinding Tools Information


PATHBUG-75CLONE – Characters are push when hit with small fast moving prim. Falcon Linden suggests using short low velocity arrows. When something penetrates a Pathfinding character (like an arrow), they are given a velocity that will resolve the penetration immediately.

PATHBUG-69llVolumeDetect(TRUE) is broken. Falcon Linden says,

I’ve found a way to preserve legacy behavior for existing objects as follows:

  1. If the linkset uses the hack and also uses new accounting, the first time it is rezzed on a pathfinding sim the hacked prim will be set to physics shape type none. Since the linkset already uses new accounting, this will not affect land impact. It may affect a small amount of content that relies on link number of higher numbered prims.
  2. If the linkset uses the hack and does NOT use new accounting, the prim will be modified such that it collides only with the terrain. Other than that, behavior should be unchanged.
  3. No new linksets can be created that use the hack, and any linking or unlinking event (other than sitting an avatar) will remove the hack.

The Lindens are looking to address the issue where optimizing physics, by using the new accounting system, causes streaming cost to skyrocket. They have some ideas but are not ready to commit to the changes yet. Hopefully I’ll have more info next week.

llDetectedLinkNum in collision_start, collision, collision_end, and land_collision events will be affected by a changing link order in the linkset and also in case #2.

Debug Code

All Pathfinding regions are running software with debugging code. This means it runs slower than the final version without debugging code will. Even with the slower code it is possible to have 50 Pathfinding characters running without slowing the region significantly.

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