[Openstreetmap] How do we handle large amount of GPS points?

[Joachim Mæland]

On Sun, 21 Nov 2004 07:44 pm, Petter Reinholdtsen wrote:

> [Joachim Mæland]
>
> > I'm Petter's Linux user, holding ~7000k GPS points and new on this
> > list...

Surely I can do a better job introducing myself...:

I'm a Linux user since 1999 and working part time as a computer 
consultant. In 2002 I participated in the forming of Oslo Linux User 
Group and I have served as a secretary since then.

I've been wardriving while working as a taxi driver in Oslo. In order to 
publish "The ultimate WLAN guide for Oslo" I needed a pixel map. By 
collecting GPS positions I've finally produced my map, but the WLAN guide 
is still waiting for some serious effort on my part. (Petter has a copy 
of my map,  please feel free to use it).

> My idea is to split between "tracks", sorted on date and with
> approximately 1 month between each split point.  I define a track as a
> set of GPS points taken in a row without any missing points.  At the
> moment, I create a new track if there is more then 3 seconds between
> one point at the next, and this is based on 1 second sampling rate.

IMHO: This is not feasible when you have such wast amounts of points 
collected while driving in a "random" pattern.

I prefer to create my "tracks" more manually and my track can last for up 
to 13 hours. In order to avoid collecting points while standing still, I 
disregard doublets and readings at speed = 0. (This is only true for the 
positions from Kismet). I have never considered your "track" as 
interesting at all... My logs are all text files, hence my need for 
naming my tracks in my dataset.

Since driving is my primary task, (only task while speed > 0), I've 
focused on 100% automatic and stupid collecting of GPS points. A more 
"collecting only" scheme might prove different and pose a different set 
of opportunities. The use of a "name current street applet" is impossible 
for me, (and not important either because Oslo is my backyard). It's 
fantastic if you are a pedestrian and plan to send the dataset to 
foreigners for actual map production.

> Oh, I am not talking about trusting them blindly, I'm talking about
> reducing the inaccuracy.  

I was never in doubt... :-)

> Check out GPS Toolkit and the september 
> issue of Linux Journal for an idea of what I am talking about.

I'll look into it. Thanks..!

> > wishlist includes: "GPS timestamp, DPOP, HDOP, VDOP and # of active

> My script collect HDOP and #satellites, but lack the others.  I plan
> to add GPS timestamp (hm, why is this timestamp several seconds off?),

What kind of receiver? How did you spot this? A few seconds is nothing 
while walking, or if you collect GPS positions only. It's a catastrophe 
if you're wardriving doing 60...

BTW: Are we talking about deviations in time _and_ position or correct 
position _and_ wrong time?

> and perhaps VDOP.  Not sure what DPOP is.

PDOP, (Sorry.. Not DPOP as I wrote): Position Dilution Of Precision

> I'm currently looking at OpenGIS SQL standard, and suspect it is a
> good idea to store the points using this framework.  I'll look at
> PostGIS next.  PostGIS is an implementation of OpenGIS SQL for
> PostgreSQL.  qgis support PostGIS.  Not sure what other tools support
> OpenGIS.

The framework for utilizing your dataset doesn't have to limit your 
framework for collecting and keeping information...

Information not seen is lost.
Information not saved is lost.
Information not kept is lost.

Wishlist for a log_to_file_tool: Simple choice of fields, as resources and 
storage buffer provided by embedded systems are limited.  :-)

Talking about embedded systems. Placing such in "random" vehicles will 
provide a tool for aligning and adjusting aerial photos and manual map 
drawings, (</good idea>). This in turn leads to: How do you plan to 
document and prove ownership of the information from which maps are 
created? How much slack do you have in this respect?

Regards
Joachim