Question regarding "Best Practices"

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Postby mahlerrd » Wed Jul 12, 2006 11:12 pm

OK, being a bit new to this particular aspect of geekery, I have a few questions that I've not found the answers to yet in my searching.

Short background to explain the question:

I'm currently wardriving some areas between home and work (with netstumbler under windows at the moment), and doing it in pieces. Quite often, I retrace steps (getting into/out of neighborhoods) or wardrive down streets where I pick up APs that I did the day before on the next street over.

Given that set up, which is preferable and by how much?

1) Drive coherent subdivisions in a single session so all points of contact with a given AP are done at nearly the same time and hopefully in the same conditions.

2) Drive coherent subdivisions in multiple sessions, but when possibe, open and append to the existing NetStumbler file from the previous drive.

3) Drive coherent subivisions in multiple sessions, not worrying about the NS files created, then merging them before uploading them.

4) Drive coherent subdivisions in multiple sessions, not worrying about the NS files created, then uploading them individually.

I would think that they are in order of highest to lowest accuracy, but that given he innaccuracies involved in the GPS and sampling frequency, there's no reason to do #1. Similarly, because of other variables, #2 and #3 are probably close enough to each other as to be equivalent in use. #4 seems to be the easiest... is it good enough?

Postby mahlerrd » Thu Jul 13, 2006 1:17 pm

I guess my question is simpler than I thought. I'm really just looking for how the triangulation works in reference to additional points recorded later. How's the weighting handle that?

This is all presumption based on what research I've been able to find and also some guessing. Therefore, feel free to whack me over the head with what really happens. :)

(BTW, I'm limiting this post to only those APs that are recorded in pretty much the same areas - not gonna get into the stickiness that could be around points that hop continents or anything... :)

When new points come in for an AP that are close, there's been an implication that the newer points are weighted more heavily. If that's the case, then it'd be better to make sure when possible to get enough data in at once to give it a good triangulated starting place.

Now, do newly recorded encounters with said AP get triangulated all by themselves and the result applied to adjust the position of the AP, or do all points get re-evaluated from scratch? It would seem the latter would be much more accurate and not much harder to do.

All right, I now realize I have no idea how the internals work. Some would say I obsess over such things, but I just find all sorts of things interesting.

Anyone have something written up already on how it works?

Postby argh » Thu Jul 13, 2006 6:06 pm

Driving a given area multiple times is preferable. Driving it all at once is sometimes more convenient. AP's are so cheap now, there are always more of them. Re-driving an area will usually always show more than the last time. Either some sort of mapping software that shows a track where you have been, or a paper map can be very useful. Especially with the cost of gasoline now, conservation of excess travel is always good...

As has been pointed out here a lot, there's nothing wrong with driving through any neighborhood once. Driving around the same block, looking lost, or driving erratically and fiddling with a laptop is suspicious. Wardriving is not illegal in USA (except perhaps California has laws about a laptop that driver can see? I'm not sure), but Joe Average thinks of it as the evil haxors stealing access, and commiting crimes. Don't park to check your email, etc. Even if you are not breaking the law, you can get your equipment confiscated and have lawyer fees to prove that you were not.

Your individual AP logs are timestamped, so there is no need to merge them as far as uploading them to Wigle. Just upload them, and let Wigle sort them out. I can't answer your questions about triangulation, at least as far as how Wigle does it.

Postby i_do_dew » Fri Jul 14, 2006 9:39 am

I wouldn't worry about the triangulation too much myself. The AP generally gets plotted along a road because that is where it is. If you hit every street in a subdivision, you would have driven right past any given AP, and the strongest signal would play an important part in the triangulation setup. At least that is my take on it. Even driving every other street probably wont affect the location too much, and how acurate do you need the information to be? It might affect the 'density' map that JiGLE generates, but probably not much either.

As for driving odd places, I've found that I get less hassle if I drive at 3am, now this doesn't work every where, but there isn't anyone awake to see you driving though their neighborhood. So unless you are doing something very unusual you won't attract police attention then either. Just make sure that when you go driving at night that ALL of your head, tail, break and marker lights are working properly, your vehicle is clean, and in good repair and not a rust bucket (heck spraypaint will fix that in a pinch). Then unless you do something dumb like run a light or drive eraticly, the police probably wont even see you. Another tip is to drive under by 5. Then even if your spedo is off, you wont be attracting attention or be giving probable cause. All this should be common (or uncommon) sense.

Apartment complexes are best done in the daytime. If anyone asks, you are looking for the office, and getting lost is a perfectly good excuse since everyone knows that guys (which I'm guessing most of us are) are notorious for not asking directions. The other things I use are yardsales for really out of the way streets. Now admittedly you might have to stop, but that is an excuse for you to leave the scanning going and really get a good image of the local AP density. How about looking at houses?

Along those lines two great ideas I had for WD vehicles are taxis and food delivery trucks. Another thing, as an experiment count how many white vans you see or rather dont normally see even though they are there in a given day. The bloody things just about have a SEP Field on them.

Lastly, somnething I read about photography and getting subjects to interact with you, applies to this as well in a side way. In order of suspicion highest to lowest are

1) Multiple males in a vehicle
2) One male in a vehicle
3) A male and a female in a vehicle

I'm not sure how these next two rate, but I would bet it is lower than the male and female
4) Multiple females in a vehicle.
5) A single female in a vehicle.

Postby ax0n » Mon Jul 31, 2006 7:25 pm

I'd never wardrive late at night. If you plan your route well, you won't ever drive past the same place more than twice, and that's only if you need to drive a cul-de-sac or dead-end. A properly planned route should allow you one pass through the neighborhood. If you aren't driving past the same house 5 or 6 times no one will notice you're there. You're just passing through.

Police love to look for the warm glow of a laptop screen in a car at night. I've gotten hassled over it before. In the daytime, take your time, go the speed limit (not below) and have a good route planned ahead of time.

As useful as re-driving a neighborhood is, wait a few days and do it later. I usually re-drive "backwards" from how I did my first run so that I'm closer to the other side of the street. I might drive a neighborhood or business park as many as 4 times. Forward, backward, and with 2 different setups (BSD Airtools and KisMAC for instance)

I always do my blatant neighborhood traversal drives in broad daylight. I have my rig running when I'm on long trips or delivering pizza, but the laptop is usually closed and in my back window. Also, those are not intentional attempts to blanket a city block, so they're networks of coincidence.

I wouldn't drive a whole neighborhood with a pizza sign on your car or in a taxi or delivery vehicle either. If you're just passing through it works well (for instance, if you're actually a delivery guy or taxi driver, and acting like one). Taxis don't drive up and down whole blocks of suburbia for hours at a time. Neither do floral vans or pizza delivery guys.

The best thing to drive is a non-descript but clean vehicle without any identifying marks on it. As was mentioned, rust buckets are bad. Burned out or broken lights are, too. Plain, non-flashy colors (stay away from Red, yellow, and other eye-grabbing color variants if you can) are best. Silver, white, black, that metallic tan/pewter color you see everywhere, maroon, and the like are all perfect. Compact car, mid-size sedan, SUV, Van or pickup doesn't matter much, so long as you don't look out of place.

People driving cars with bright colors, big chrome wheels, loud stereos and exhausts are the ones people notice and call the cops on.

As far as AP placement, WiGLE averages all the reported locations. Don't worry if the AP keeps moving around a little or you don't see it in the exact same location between your map and WiGLE's. Unless the AP is showing really far away (by a block or more) from the actual location, it's not a big deal. If it's too far off it might be a problem with your log file format, your software, or your hardware

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