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Old 10-16-2014, 01:17 PM   #65
vicky_molokh
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Default Re: (Unofficial) FAQ of the GURPS Fora

Sense Rolls, Stealth and Camouflage

Quote:
Originally Posted by Kromm
This is a long response, so I've had to split it in two to avoid the character limit for a PM. Note that this took a lot of time to write, so I simply can't justify follow-up comments. I hope these answers will suffice!

Quote:
Originally Posted by vicky_molokh

Hearing vs. Stealth
Moving quietly normally takes a Stealth roll contested by Hearing. Hearing rolls suffer a -1 penalty for each doubling of distance relative to the 'standard distance'. What is the 'standard distance' at which the Hearing value in the Contest is unmodified?
I'd go with the 1/4 yard implied by High-Tech, p. 158 if the person is truly stalking. The Stealth skill gives -5 when Moving faster than Move 1, however, which is functionally equivalent to +5 to Hearing, making the distance 8 yards at Move 2+. That's too coarse-grained, so I'd prefer to say that base distance equals the stalker's Move. Thus, any combat movement (Move 1+) is audible at full Hearing at one yard; sneaking to within stabbing distance is a simple Quick Contest of Stealth vs. Hearing; and the High-Tech case assumes someone moving at Move 0.25.

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Originally Posted by vicky_molokh

The only indication I've found was High-Tech 158: 'Leaves rustling, stalking person 40dB(A), 0.25 yards'; that seems to result in a Hearing-2 roll at 1 hex, which is consistent with the Hearing roll to figure where the unseen opponent is in combat (B394).
That -2 is more for "surrounding noises" (p. B358) than for distance. It's also a simplification; note that neither the distance nor speed of an unseen attacker affects this Hearing roll. I wouldn't attempt to rationalize this. If you must, then use standard distance = Move and apply an extra -2 in a fight, so that someone running at Move 5 is heard at -2 at 5 yards, -1 at 2 yards, no modifier at 1 yard. Just stepping a yard means he's heard at -2 at 1 yard (which is the most usual case in combat).

Quote:
Originally Posted by vicky_molokh

More on Hearing
The table seems to produce very low chances of hearing normal stuff, such as a mere 50% chance of hearing a normal conversation at 1 yard or a loud conversation or noisy office at 4 yards. Should there be some sort of positive TDM under most noncombat circumstances, perhaps +6 (so that people at 1 yard could always hear each other)?
Vision rolls get +10 for "in plain sight." Those use a progression where every -6 is 10 – i.e., Vision gets an effective x10^(10/6), or about 50, range in unchallenging situations. The equivalent for Hearing would be +5 or +6. I'd pick +5, as it's easy to remember and gives ordinary conversationalists a Hearing roll of 15 at 1 yard or 14 at 2 yards, which allows for the occasional "Sorry, what was that?" moment that happens in real life.

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Originally Posted by vicky_molokh

Sense of Smell
To turn a Canadian song quote into an actual rules example . . . 'I hate it when they go out, and we stay in // And they come home smelling like their ex girlfriends' - well, what are the modifiers to differentiate between two people or whether one person carries the scent of another like that?
That's more a research question than a rules question. As a rough guide, call it -4. That way, Discriminatory Smell's +4 cancels it out. Ordinary people would be rolling against 6, which seems believable given our atrophied olfaction. If the objective is to spot an impersonator, I might give a bonus of +1 to +4 if the person rolling is intimately familiar with the subject – say, +1 for a friend, +2 for a best friend, or +3 for a lover, and another +1 if you've lived with the subject.

Quote:
Originally Posted by vicky_molokh

Smell, Stealth and Range
Stealth is at -5 against Discriminatory Smell; that clears up the stealth part. The unclear part is, how do range modifiers work for smell? Yes, a wind in either direction would throw off the table, but at least what are the default modifiers?
That has never been established. I'd apply standard range modifiers, a separate bonus or penalty for windspeed, bonuses for large sources (say, equal to SM) and strong smells, and up to +5 (for "extra time") for persistent sources. Thus, a huge factory (SM +10) that's a mile away (-18), spewing a foul smell (+4) constantly for days (+5) would be detectable at Smell+1, or possibly Smell+2 or Smell+3 with the right wind. A human (SM 0) a yard or two away (0) wearing strong perfume (+1) in a still room would be detectable at Smell+1 when she walked in, or Smell+2 if she had a lot of perfume on – and you'd add up to +5 after she'd been in the room for a few hours. So don't try Stealth if you like perfume!
Quote:
Originally Posted by Kromm
Quote:
Originally Posted by vicky_molokh

Scanning Senses
Scanning senses have a designated range, after which they start accumulating stacking -2 penalties per doubling. But what are the modifiers to the Sense roll within the designated range?
There are none. To quote Active Sensors, p. B472: "They can sense objects out to their rated maximum range at no range penalty."

Quote:
Originally Posted by vicky_molokh

I mean, I suppose detecting something close to the sensor should be easier to detecting it near the very edge of the designated range. +2 at point-blank? It's kinda weird to have only a 50/50 chance to detect things real close, or even a 25% chance to miss a human-sized target at point-blank with a LADAR or the like. Should they benefit from the Plain Sight modifier? Benefit from it only to offset SM penalties and range penalties?
I would avoid most such complications. Our goal was to get away from the Third Edition model with range penalties and Scan ratings. That said, "in plain sight" appears to be nearly universal, and should apply to these senses. However, if the target is being even a little evasive, or if there's any cover – which is to say, in almost any combat situation – I wouldn't give this bonus. If a high-tech sensor shouldn't believably miss targets inside its range, that's what Acute Senses are for. Acute Radar and Acute Ladar are legitimate, and baseline Scanning Sense acuity assumes human perceptions, not technological ones.

Quote:
Originally Posted by vicky_molokh

Stealth and Camouflage
Camouflage can be rolled to prevent being seen even after a failed Stealth roll; a stationary ambush only requires Camouflage, without Stealth. So Camouflage is of use on the move if vision is more of a concern than hearing . . . but regarding vision, does the Plain Sight modifier apply to trying to see camouflaged targets in the Quick Contest?
No! By definition, camouflaged people or things aren't in plain sight.

Quote:
Originally Posted by vicky_molokh

(On one hand, by the logical reading of the bonus, it shouldn't, on the other, the numbers get weird if just trying to camouflage suddenly denies a whole +10 bonus to the enemy. In fact, this question applies to Stealth too. So far, the cleanest way for me was assuming a +10 included by default, and reduced depending on the amount of cover available down to +0 for ideal cover, with no roll available through a complete wall.)
The +10 never applies in hostile situations where one side would rather not be seen. It's specifically and exclusively for situations where the item of interest cannot avoid being seen . . . Thus, in most cases, using Camouflage or Stealth doesn't instantly give -10, because even someone without those skills would deny the +10 for "in plain sight" unless standing around like an idiot. I'd let any person avoid giving potential foes that +10 simply by asking, though they'd automatically be "up to no good" in the eyes of any cop or soldier (thus the "approach in the open with your hands above your head" order).

Quote:
Originally Posted by vicky_molokh

Camouflage says it either makes the user unseen, or provides a -1 to be seen/hit. When does it merely blur the outline for this -1? Can it provide a nastier penalty than -1 and under what circumstances if yes?
That -1 is for a blurry outline vs. ranged attacks. Anything more serious would require advanced tech or superhuman abilities. Obviously, smoke could do it with fairly low tech, but that is unsubtle concealment, not camouflage per se.

Quote:
Originally Posted by vicky_molokh

Sense rolls in general
What amount of time does it usually take for a sense roll, i.e. how soon another one is possible? Should Time Spent modifiers apply, e.g. for slowly scanning everything up to the horizon?
Canonically, Sense rolls are free actions and not subject to time modifiers. If you fail, you can't retry until something changes to improve your Sense roll: the range decreases, the target turns on bright lights or sounds a horn, whatever. I can't think of a fair modifier that wouldn't be a free bonus for everyone outside of combat, though I might be nice and grant someone who's exclusively scanning and doing nothing else the same +2 that Aim would give after three seconds.
Quote:
Originally Posted by Kromm View Post
Stealth prevents being seen and being heard. Its main uses are hiding from sight behind concealment or in shadow, and treading lightly. However, very little in the way of gear gives a bonus in that situation; mostly, the more gear you have, the harder it is to hide, thanks to encumbrance. Dan was describing equipment bonuses, not skill effects.

Camouflage only prevents being seen. Its main use is hiding from sight by breaking up outlines and disguising oneself as part of the environment. A lot of gear gives a bonus in that situation. Again, Dan was describing equipment bonuses, not skill effects.
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Last edited by vicky_molokh; 02-18-2016 at 04:35 AM.
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