Category:Detection

Detection is Oblivion's stealth mechanic. The concept isn't complicated: every actor has a degree of awareness of every other nearby actor, called a detection level. If this detection level is above a certain threshold then the searching actor (the "detector") is fully aware of the hiding actor (the "target"). The detector can then attack, offer a greeting, report the target's crimes, etc. If the detection level falls below the threshold again, the detector "loses" the target and can no longer interact with it.

Quite a few variables go into calculating detection levels. They fall into three basic categories: Sight, Sound, and Sneak Skill. Sight describes how well the detector can see the target, and only matter if the detector actually has a direct line-of-sight. Sound measures how much noise the target is making from movement and from being in combat. Skill measures the sneak skills of the detector and the target. In all three categories the distance from the detector to target plays a very important role.

Some of the conditions in the formula are still under investigation. In particular, the detection does not always correctly recognize when the target is in combat. Whether this is specific to the player or due to some other bug is not yet known.

The complete formula for Detection Level is given below. Because the formula is so complicated, it is broken into smaller pieces and organized in a table. Conditional terms are enclosed in square brackets, e.g. "[ + 400, if target is yellow]" means "add 400 if the target is yellow, otherwise ignore this term".

Detection Level Formula

0

-100

fSneakBaseValue 
[ + fSneakTargetAttackBonus, for a single frame the first time the target attacks the detector]
[ + SoundBonus, if target is not swimming]
[ + fSneakSleepBonus, if detector is sleeping]
[ + SightBonus, if detector is awake and has line-of-sight to target]
+ SkillBonus

fSneakSoundsMult * DistanceFactor *
(
  [ MovementFactor, if target is moving and target Sneak mastery < Expert]
  [ + fSneakTargetInCombatBonus, if target is in combat]
)
[ * fSneakSoundLosMult, if detector has no line of sight to target]

(
  fSneakBootWeightBase
  [ + (fSneakBootWeightMult * (tgt boot weight)), if tgt Sneak mastery < Journeyman ]
)
[ * fSneakRunningMult, if target is running ]

fSneakLightMult * DistanceFactor * LightFactor * ChameleonFactor * BlindnessFactor
[ * fSneakSwimmingLightMult, if target is swimming]  

fDetectionSneakLightMod + 
(
  (light level on target) 
  [ * fDetectionNightEyeBonus, if detector has Night Eye]
)

1 - (Chameleon level of target)/100

1 - (Blindness level of detector)/100

fSneakSkillMult * 
(
  (detector Sneak skill * DistanceFactor)
  [ - target Sneak skill, if target is sneaking and not in combat]
)

1 - (distance between detector and target) / MaxDetectionRange

fSneakMaxDistance 
[ * fSneakExteriorDistanceMult, if in exterior cell]

Detection Thresholds

If the Detection Level is greater than a certain threshold, the detector can becomes aware of the target. The thresholds are:

A final note: The target-is-in-combat bonus is fairly significant. Combined with the much lower combat threshold, this can make it very difficult for an actor to return to hiding once a hostile actor has seen them.

Performance

Every NPC/Creature that is high processing will make approximately three rounds of detection calls per second. Those detection calls will be made against everyone within the detection range of the actor, not just against the player. It also doesn't matter whether the target is sneaking or not. Sneaking merely modifies the target's ability to be detected.

Therefore, as the number of active actors in an area increase, the number of detection calls made increases exponentially.

In the above examples, this assumes that everyone is within the detection range of everyone else.

In exterior locations, actors are rarely so clumped together except in high traffic areas such as the Market District. But then again, exteriors have default range of 2x the interior detection distance, which is roughly four times the area.

With default Oblivion, you will rarely run into large numbers of NPCs/creatures that are densely packed. But in a heavily modded Oblivion, this can have a noticeable effect on performance when the player enters highly populated areas. Detection is probably not the only Oblivion feature that behaves like this, but it's the one that we for sure know behaves this way consistently all the time.

Any mod that alters the detection formula (such as SDR) in combination with mods that increase the population density will therefore potentially impact performance as well, depending on how the mod is designed and implemented.

Detection Functions

IsActorDetected does not appear to call the detection formula, since it does not require both the target and detector to function. It is the simplest method of determining whether an actor is being detected at any given time.

GetDetectionLevel does not appear to call the detection formula either, and may be the most efficient method of determining the detection result of a detector/target pair, especially when a mod that alters detection (like SDR) is in the load order. Although it is unknown whether or not the result is based on Oblivion's native detection results or the detection altering mod's results. The theory is that each detection result of target to detector is tracked internally, and is merely looked up by the GetDetectionLevel function.

GetDetected, on the other hand, forces Oblivion to run the entire detection formula, and therefore any mod that alters or hooks that formula will have its sub-scripts called. Depending on how often it is used, this could potentially cause performance issues.

Notes

• Dead actors seem to have their detection status "locked in" at whatever value it was when they died. This means an actor aware of the player when the player kills him, will always be considered aware of the player (though this does not matter since the actor is dead). It is therefore important in scripts which check detection levels to also make sure that the "detector" is, in fact, alive, in addition to checking other detection settings.
• The bug above also applies when SetUnconscious is used on an actor, until the effects of that command are reverted.

See Also

Sneak

GetDetectionLevel

GetDetected

IsActorDetected