Visibility rules

[condor]

This tread is intended to gather some advice and insights on guidelines for general visibility rules, that are dispersed throughout rules books. I miss a structured set of instructions when planning realistic patrols, search operations, castle walls manning, etc.

I don't know if this has been discussed elsewhere, but I could not find it.

These general visibility rules could address some of the following questions:

1) How far can a man spot another man moving on the grass, assuming he is on a castle wall, like 15ft above the ground, and under perfect light and weather conditions? Or, put in other words, on average, how far a person with Per of 10 could roll against 12?

2) How far can a person recognize a friend in the same conditions?

3) How far can a soldier keep track of another one in differente environments, like a deciduous forest, or a night grass field?
It would help to answer questions of how much land ten man can sweep with a search team in one hour.

Thanks in advance!

[Anthony]

For GURPS, you're mostly looking for the Plain Sight rules. If you want realism, this is the kind of thing the military has studied, you should be able to find papers on the internet (I have no links at the moment; haven't looked at this in quite some time).

[Anaraxes]

The distance at which you can spot someone boils down (all else being equal) to how much of a range penalty you can soak on your vision roll. There are other modifiers to that Perception roll, of course -- things like darkness, camouflage, or those trees in the way. Being "in plain sight" is a +10, so that makes things much more visible at a distance.

This past thread has some useful discussion.
http://forums.sjgames.com/showthread.php?t=130631

Realistically speaking, you'll also have to consider terrain. Also the horizon distance, if you're talking really long distances and "flat" terrain.

(The horizon on Earth from a 6' / 2m height -- human eyeballs -- is about 3 miles / 5 km. Further than that, and the object is sliding down behind the curve of the planet. Increased height and tall objects to view can greatly increase the horizon distance; you can find calculators on the web it if matters.)

[condor]

Originally Posted by Anaraxes

The distance at which you can spot someone boils down (all else being equal) to how much of a range penalty you can soak on your vision roll. There are other modifiers to that Perception roll, of course -- things like darkness, camouflage, or those trees in the way. Being "in plain sight" is a +10, so that makes things much more visible at a distance.

So, in raw, the answer to question #1 would be the distance that makes the perception +10 of an average man drop to 3. In this case, -17, or around 1,500 yards.

Originally Posted by Anthony

If you want realism, this is the kind of thing the military has studied, you should be able to find papers on the internet (I have no links at the moment; haven't looked at this in quite some time).

If by any chance you remember of any of these links or papers, I would really appreciate. Maybe it is my Research Skill fault, but I could not find anything in Google.

Edited for correcting:

Originally Posted by Anaraxes

Actually that was Anthony's comment.

[whswhs]

Originally Posted by condor

So, in raw, the answer to question #1 would be the distance that makes the perception +10 of an average man drop to 3. In this case, -17, or around 1,500 yards.

If you want to see them, yes. It's more complex for recognizing them. On one hand, once you've spotted them, discerning their features takes a +20 bonus (see GURPS Powers: Enhanced Senses). But on the other, you have to discern features that are a lot smaller than an SM 0 human!

[condor]

Originally Posted by whswhs

If you want to see them, yes. It's more complex for recognizing them. On one hand, once you've spotted them, discerning their features takes a +20 bonus (see GURPS Powers: Enhanced Senses). But on the other, you have to discern features that are a lot smaller than an SM 0 human!

If we consider that a character knows well someone, a GM could let the player use proportions of parts of the body to spot him or her. Like the head, thigh or forearms measures crossed against each other. That would give a -6, and as a rule, an average person would recognize someone he knows at 150 yards.

http://www.telegraph.co.uk/news/scie...s-no-help.html

To tell one face from the other, a person would have to compare the lenght of facial features with one another (2 or 3 inch). That would give like -10, or, 30 yards.

That would be a reasonable answer for #2.

[Anaraxes]

Originally Posted by condor

you remember of any of these links or papers

Actually that was Anthony's comment. But if it helps:

Basics of squad/platoon level infantry operations are in US Army Field Manual 7-8. They have a few diagrams of typical spacing, though the days of drilling to precise regulation distances are long gone. For other tasks, you might try searching for "search theory" and "search and rescue". Various organizations have plans for categories of search, depending what you're looking for, all the way down to those searches you've seen on cop shows, where llines of people a yard apart are sweeping a field and looking for evidence.

[condor]

Originally Posted by Anthony

If you want realism, this is the kind of thing the military has studied(I have no links at the moment; haven't looked at this in quite some time).

That was a great hint. Thanks!

http://theantimedia.org/100-military...load-for-free/

In fm90-5 manual (Jungle Operations), page 1-3 it is written that in Tropical Jungle, visibility is less then or equal 55 yards.

https://fas.org/irp/doddir/army/fm90-5.pdf

Annex K of FM 7-93 lists some night operation relevant distances recognition:

http://pdf.textfiles.com/manuals/MIL...tober_1995.pdf
Vehicle headlights - 4 to 8 kilometers
Muzzle flashes from single cannons - 4 to 5 kilometers
Muzzle flashes form small-arms weapons - 1.5 to 2 kilometers
Flashlight - up to 2 kilometers
Bonfire - 6 to 8 kilometers
Lighted match - up to 1.5 kilometers
Lighted cigarette - 0.5 to 0.8 kilometers

The MOUT, Marine on Urban Terrain operations manual, has an interesting table:
http://www.marines.mil/Portals/59/MCWP%203-35.3.pdf

Tank crew members, soldiers (tell them appart from civilians?), antitank gun, antitank missile launchers 500m
Tank APC, truc (by model) 1,000m
Tank, Howitzer, APC, truck 1,500m
Armored vehicle, wheeled vehicle 2000m

Also, I found a very interesting cognitive scientist paper on face recognition. Realistically, facial recognition is something between 25 and a 150 feet, or around 8 to 50 yards:

http://cognitrn.psych.indiana.edu/bu...eyDistance.pdf

https://www.innocenceproject.org/can...-of-feet-away/

I am still searching more daylight info, distances according to the kind of vegetation and variations in contrast (background and object).

[Bruno]

Some of the things that can disrupt facial recognition are interesting. Ignoring brain damage and suchlike, seeing a person out-of-context can prevent recognition.

If you've only ever seen someone in uniform, you'll likely have trouble recognizing them - particularly away from the building they work in, if that's the only place you've seen them. Your brain can get a little lazy and include some of these environmental factors as part of their "face".

Some kinds of face paint or makeup make a person hard to recognize, some don't. And of course things like face scarves, hats, and goggles or sunglasses (common parts of outdoor equipment and of military equipment) can make it pretty darn tricky.

But recognition isn't all about faces - I'm kinda dreadful at facial recognition because of some mild drain bamage (have trouble recognizing my partner and my own mother sometimes :P) but posture, gait, general body language, and of course voice are all helpful. Less reliable but still helpful are haircut, facial hair (if any), glasses, and clothing, and if you can't do the face for whatever reason, general context is enormously helpful (if she's in my mom's apartment and kinda looks like my mom, it's my mom).