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Position Ambiguity [was] Re: [aprssig] findu.com....

KC2MMI (Jared) kc2mmi at verizon.net
Sun Jun 11 22:44:02 UTC 2006


Bill, are you being disingenious, or did you not understand the context of James
complaint?

"Will you do the same for every position you supply to the APRS system?  Just
include a note with every beacon indicating that your position may be
inaccurate.  Wouldn't be necessary if you could certify the accuracy of your
position in every packet."
  The position generated from a GPS is known to be accurate within the norms of
the GPS system, typically 3-10 meters all things being considered. The problem
is, APRSWorld, and any software using the Tiger maps of the NavTeq maps (or
several others as a base) is displaying those geographic coordinates INCORRECTLY
on the street maps they use.
 As GPS users, it is easy for us to know the accuracy inherent to the system,
therefor when we send a position that is designated as a GPS position, using the
designated default datum, we know the accuracy inherent to that position. I'd be
glad to send EPE but as you should certainly know, APRS does not provide for
sending that. APRS and GPS both are fixed and well known constraints. The errors
from bad data in mapping systems are not, they are unknowns to the ordinary
user.
  The norms of mapping and information graphics all say that using a start which
covers perhaps a 50-foot radius, when it is being used to plot a 200-foot
radius, is simply wrong. And easily corrected.
 Unlike your request to send data that is not supported by the systems, cannot
easily be sent, and has a known uncertainty in it, among other differences.

"If you supplied the necessary information with every position packet you
send, this could be done for you too." What could be done for me too? Correcting
the display? As I said, there's nothing wrong with the data being sent, there's
no reason (or easy means) to provide more data. The problem at hand is that the
existing data is being displayed incorrectly. Yes, it is a simple matter of
objective right and wrong, the data is being displayed wrong and it is easily
displayed "right" by changing the display icon.

"FYI, the census bureau data is supplied in vector format, not as an image." I'm
aware of that.
"APRS World simply renders the vectors on an image." Are you sure about that? Is
it Jim who is rendering those Tiger Maps, or is he getting his maps from another
source? And again, that doesn't matter. I'm asking where he gets his data--not
just the map, but the position indication and the default star marker. Is he
generating the map? Is he generating the marker icon? As long as he is
generating the *icon*, that's enough, all he has to do is generate it in a
larger size. It would be even better if the size was related to the display
scale of the map, so the star represented a set range circle matching the scale
of the map.
 And as Bob indicated, it is also normal and "right" to display a mileage scale
with every map.

"Yep, James should do that for every position packet he displays on a map
too<g>."
  You really don't get it, do you? Or are you looking for a flame war? James
doesn't need to present the error notice for *any* position packet, much less
for *every* packet. The error warning can be a fixed slug that is on every page,
the same way that his map copyright notice or any other boilerplate is already
there. The extra time/load on the server is zero, the bits for the screen are
already being sent regardless of what the boilerplate says.

"Interesting.  Since virtually every street mapping product for the US was
originally based on the TIGER files,"
 You are misinformed. The source of many maps are USGS topo maps and state
planimetric maps. The state planimetric maps are usually of extremely high
accuracy but you have to PAY to obtain that data from most states for commercial
use, which is why some wanna-be map makers grabbed the TIGER maps instead.
DeLorme's famous paper map books were, for many years, simply not available for
some states because they couldn't afford to buy the good data. ESRI and other
commercial vendors have not used the TIGER maps for their bases either.

"How can you say anyone is misappropriating files the Census Bureau has
placed in the Public Domain?  "
  How I can say it, as exactly as I did say it. The files are meant for
demographic studies. Using them for navigation, when they are expressly not
issued for navigation, is misappropriating them. Misappropriate means "to use
wrongly", not just "to use illegally". The primary definition is to use
something WRONGLY and using the TIGER maps for navigation purposes, is wrong.
According to the source.

"You are basically accusing every mapping vendor in the US, and all other
users of Census Bureau Tiger file of misappropriating government property.
Get real." You can apologize for that after you realize you didn't understand
the word "misappropriate" and you didn't understand where map makers got their
base maps from, as noted above.

"If you can get all vendors of US mapping data to do this, than APRS World
should do it as well.  "
  Ah, that's a worthless point to raise in this venue. James made a complaint,
we're addressing HIS complaint and HIS software here. What his software should
or should not do, has nothing to do with what some vendors (not the "all" you
proclaim) choose to do. "All" vendors aren't doing anything uniformly, and this
is not the venue to argue about what they should be doing.

"You certainly need to learn something about cartography before you criticize
someone who is EXTREMELY well versed in the science and application of same."
 Ah, the infamous ad hominem attack when you run of facts to discuss. James is
extremely well versed? And I'm not? You know both of those things for facts?
Then he also would have known his display is incorrect. Correct me if I'm wrong,
I thought James started this as a *student* project in college. I have no idea
what his credentials in your unspecified "science and application" are, but
unless he's been working in the field for a while, you'd be presuming too much.
And if he was an expert? Experts will be the first to tell you, sometimes they
still get things wrong.

 As James knows, I had to pull teeth and do extensive research--including some
with academics that he knows--in order to find the base problem in the TIGER
maps. It isn't readily known or available to the public, including "experts".
I've done my research, and he knows it. I've traced datum problems back to Dutch
surveys of the 1600's, and the state engineers who maintain modern planimetrics,
and the USGS, are aware of them. It's the HAMS, the APRS users, and the folks
who naively misappropriated the TIGER maps, who are in error here. All of the
real experts--the state survey offices and academic professionals--know it.

The only question is, should hams continue to be the "ham fisted amateurs" that
the Marconi operators belittled them as? Or can we do better, and make our
presentation reflect its limits?






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