[aprssig] traffic reporting
steve at dimse.com
Wed Apr 6 09:40:19 CDT 2005
On Apr 6, 2005, at 10:13 AM, Jim Lux wrote:
> The problem with reporting only anomalies is that it requires some
> knowledge. This is the same problem with the traffic reports on AM
> They never tell you that the 10 is a parking lot, because it's ALWAYS a
> parking lot during rush hour, so it's not news to a local driver.
XM has channels for 20-odd major cities that do include areas of normal
delays, I've found it very useful when traveling.
> the optimum scheme is just to periodically (every 5-10 minutes)
> (an a FCC and copyright legal way, of course) the background image from
> http://www.sigalert.com/ or from the Caltrans website as a standard
Looks like the sigalert site has the same constraints the one in South
Forida which preclude retransmission. The CalTrans site seems to have
the same raw info, but not presented in a concise form. It might be
possible to develop a screen-scraper, or maybe deep inside there is a
machine readable form of the data I didn't find in my short perusal.
In South FL, there is no free government site, the data is sold by the
government to a small number of commercial services that provide it
only under restrictive terms, and this is the situation in many areas,
traffic data is seen as a source of income.
> Perhaps in pieces, spread over the 10 minutes, a'la
> teletext, so you don't block all the other APRS traffic.
When I was using the Earthlink AVL, it had the capability to receive 40
character messages, I had code to break up a small portion of a weather
radar image and send it in chunks for display in my truck. It worked,
but was slow and unreliable. That image on the sigalert site is very
large, and would take a long time to transmit, if you wanted to get it
across in 5 minutes it would probably take the full 144.39 bandwidth.
On the other hand, it represents essentially 2 bit data for each of the
traffic sites, a couple hundred bytes at most. Distilling it down to
segments of highway would take even less bandwith (probably a single 50
byte packet would do it) but receiving software would need to know the
location of each segment to display it properly (of course the proposed
solution of breaking down the image would also require new client
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