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

Bill Diaz william.diaz at comcast.net
Sat Jun 10 23:11:48 UTC 2006


Jared,
  See below:

>-----Original Message-----
>From: aprssig-bounces at lists.tapr.org 
>[mailto:aprssig-bounces at lists.tapr.org] On Behalf Of KC2MMI (Jared)
>Sent: Saturday, June 10, 2006 12:56
>To: aprssig at lists.tapr.org
>Subject: Re: Position Ambiguity [was] Re: [aprssig] findu.com....


>James-
>
><<The issue that I have with KC2MMI's complaints on position 
>is that he wants me
>to fix the data APRS World maps are drawn from. >>

>Not so. I don't know how you draw that conclusion, but I do 
>not want or expect
>you to fix their data. All that I would ask, in your case, is 
>for you to alter your presentation of that data, or, in the least, 
>just stick a marginal note on *your* screen that pointed out the 
>error.

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.

> Now, I don't know how you are drawing and presenting the 
>data. If you are calling up their map, and overlaying it with one glyph 
>(sprite, icon, whatever you know it as) for the data point, you can simply
use a 
>larger glyph. Instead of a start that is 10(?) pixels across, use one that
is 40 
>across. Same code for everything except the glyph you use.

If you supplied the necessary information with every position packet you
send, this could be done for you too.

> If you are calling up the complete image as one image from 
>the other source, then perhaps you can't control it. 

FYI, the census bureau data is supplied in vector format, not as an image.
APRS World simply renders the vectors on an image.

>OK. How about a little note someplace next to the map that says 
>"The position shown may be off by 1/10th of a mile." (I've
>seen that much error, obviously the extent should be investigated.)
> You *can* easily do that, can't you?

Yep, James should do that for every position packet he displays on a map
too<g>.

><<That data is from the Census Bureau. If they have money and a staff to 
>put TIGER together, how can I (with no money and no staff) possible be 
>expected to "fix" their data. I don't even have the GIS tools to easily 
>modify the TIGER data.  ... I'm not a cartographer. The US Census 
>Bureau apparently is. Submit your changes to them and when they come out
with new 
>TIGER data, >>

>See, that's another set of misperceptions. I've spoken 
>directly to the TIGER folks at the Census Bureau. They will be the first 
>ones to tell you that TIGER is intended for the display of population 
>demographics data, NOT NAVIGATION, and
>it should not be used for any navigational purposes. What this 
>means is that literally, some of their road upates are made by sending out 
>someone in a car who said "I drove eight tenths of a mile approximately 
>south-southwest on this new street called....Please enter it that way 
>on the map."  Their purpose is to show you where "123 Main Street" 
>and "256 Broadway" are located, in relation to the street and block 
>entities, so you can see which block is in which voting 
>district, and so forth.

>Please note that is all data from and for STREET ADDRESSES and 
>not GEOGRAPHIC data. While the USCB has correlated geographic positioning
to 
>their street information ("geocoding" the street addresses, a word which 
>can have several slightly different meanings) they only intend the
geographic 
>information to be incidental, so you can tell that "Smallville" is about
eight 
>miles away from "Anytown", and nothing much more.

Interesting.  Since virtually every street mapping product for the US was
originally based on the TIGER files, you should contact all the street map
vendors and ask them to include a note about the inaccuracy on each map they
display.  Lets see how far you get with them.

>The USCB are *not* cartographers, they'll tell you that. They 
>limit themselves to demographic displays, and the rest is done as best they
can 
>with the limited resources they can. They asked me to contact my 
>CongressCritters (my word, not theirs) to complain about funding, because
they 
>are very much aware of these problems--but they have no budget to correct
them.

>Every year the USCB does what they can, typically 
>correcting/updating 100 counties in the US. That's all they can fund. It is
hard to 
>blame the USCB for bad data, when the problem is that all of us computer
users 
>have misappropriated their data, and it is as much our error as theirs, for
not 
>finding out the limits beforehand. (You've really really got to dig at the 
>USCB to find out their "maps" are not intended for traditional use, but for
demographic
>generalities only.)

How can you say anyone is misappropriating files the Census Bureau has
placed in the Public Domain?  

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.

><<But tell ya what: I'll happily give you a free week of use 
>of the APRS World map server.

>> As I've said in the past, thank you. Seriously.


><<I can't fix the data. My choices are to present the data as 
>given to me or to not provide the service at all. I would be happy to add a

>notice to APRS World that says it is not to be used for life support 
>applications. Should I do that?>>

>I have suggested something similiar many times. Not "life 
>support" but something that simply says the data source is NOT as precise 
>as it appears, there can and will be some error. I would expect most APRS 
>users, like most hams, and in turn most of the general population, knows
nearly 
>nothing about mapping datums and error sources, especially about obscure 
>ones like how the TIGER maps happen. So instead of ignoring the error and 
>allowing it to mislead people, why not give them the heads-up, if that's 
>all you can do? If you mop a floor, you put a "wet floor, caution!" sign
out. Or, you pay 
>the jury award when someone slips and falls on it and breaks a hip. (I know
some 
>businesses who have paid those award, and still refuse to put out a sign
because 
>it is too much effort.)

If you can get all vendors of US mapping data to do this, than APRS World
should do it as well.  

>
><<APRS World's source code is open source. ....
>My asking you to contribute code is a perfectly reasonable thing to
>do.>>

>I wasn't aware of that. Asking me to contribute code would be 
>reasonable--if I  were a programmer.<G> Being a "programmer once removed", 
>if I may coin a phrase, can I ask you again whether APRSWorld grabs one 
>screen shot of the map plus the overlaid position mark (star, glyph, 
>icon, etc.) all from the  same source? 

There is an unwritten rule concerning ham radio applications and APRS
applications in particular.  "Those who code, rule".  If you don't like how
the application works, you are free to write your own.  If you are not a
programmer, you can learn, as many hams have done in recent years.  We have
all benifited from these endeavors.  Perhaps you could even learn something
about cartography in the process?

You certainly need to learn something about cartography before you criticize
someone who is EXTREMELY well versed in the science and application of same.


Bill KC9XG

>Or do 
>you have that option to simply change the size of the star, by 
>using a larger
>one?
>







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