Lowest cost proximity detector

I have an action I want to trigger when a specific person gets within a certain area. I have two possible solutions:

1. A timer-driven sensor scan that starts with a large range (10m) and a slow rate (20sec) gradually shrinking and speeding up until the trigger range is reached (about 2m). Timeouts move the scan range back out and slow down if no hits at the smaller range. Once triggered it stops scanning until the next day by setting a long timer value.

2. A transparent prim covering the 2m radius target area, with llVolumeDetect on and a collision_start action. Comparing llGetUnixTime to a saved timestamp inhibits the response to once a day.

#2 should have the least lag effect, because I only expect a trigger to actually happen every few days. But I can't get the prim (a half cylinder) to be fully transparent. It only wants to go to 90%, leaving a ghostly outline.

Does this mean #1 is the only way to do it?

I have given you a texture called totallyclear. It will make your prim invisible.

If you need to see it later, you can by turning on Highlight Transparent on the View menu. Ctrl-Alt-T is the shortcut to that.

llSetAlpha(0.0,ALL_SIDES);

If you're really interested in detecting only one specific avatar and want to cut the amount of lag contribution to a minimum, there is also llCollisionFilter(). We don't tend to use it much because...well, this is probably about the only application that can reasonably make use of it. Heh.

http://www.lslwiki.net/lslwiki/wakka.php?wakka=llCollisionFilter

If you're doing spherical ranges you can set a slow rate sensor or a single volume detect prim that pushes object/avatar keys to a list. Then what you do is use llGetObjectDetails() to get the position. After that a simple if(llVecDist(llGetPos(), other_pos) < 10.0) will tell you if the object is within 10m, and have another if block to check for 2m range.

True. If you know the key of the avatar you're looking for, you could simply use llGetObjectDetails() in a timer loop. That easy. If an empty list is returned, they aren't in the region (and you might increase the timer period until the target enters the region).