[Xastir] Tiger 2007 shapefile issue...a beaut

[Richard Polivka, N6NKO]

Alright, here are the details of the equipment:

 - About 7' of 1.25" PVC pipe with a hole through it for a rubber band 
to hold onto GPS unit
 - US GlobalSat BT-359 Bluetooth GPS receiver - chipset: SiRF STAR-III/LP
 - Cingular 8525 smartphone
 - "Turbo GPS" software Ver 2.00 alpha 8

Did testing in NMEA mode. SiRF mode has the longitude really messed up. 
I think I will hit up a couple of BM's and see how bad the data is. 
Maybe it may be recoverable by applying Finnegan's Fudge Factor.

Trying to resolve a garbage can using just L1 and a consumer grade GPS 
will just give you garbage when you have only ddmm.mmmm to use. I went 
in knowing what the maximum resolution is: one count latitude = 0.2222 
meters; one count longitude = 0.1630 meters. I was willing to spot the 
rig +/- five counts moving so I would say that I made my self-imposed 
limit. I thought that it would be worse.

Using a 2m range pole with a surgical sharp pick at the end will do your 
feet some damage. You probably have a outrageously overpriced choke ring 
antenna on top and that in itself is a real headknocker in its own 
right. I did a test with this setup here at home one day over four 
hours. I pulled out the NMEA $GPGLL sentences that were at PDOP= 0.6 and 
mapped them out. The resulting x-y graph presented an almost circular 
pattern of a diameter of 8 counts. Averaging the readings put the 
average right in the middle of the chart. I am quite happy with this 
mashup. Not professional grade but it will do the jobs that I need it to do.

Have a good week. Now to pull up a property survey to figure out an 
issue for someone.

Best Regards,

Richard, N6NKO



Gerry Creager wrote:
> Richard Polivka, N6NKO wrote:
>> Gerry,
>>
>> Yes, the coffee has kicked in and I had egg-on-face for breakfast. 
>> The map in QGIS looks just like the same as the aforementioned area 
>> when at full extent view. Zoomed in, it works.
>
> The egg comment has to do with a Census screwup... It's Census, it's 
> gonna happen.  Their view of GIS has been "interesting" for some time.
>
> I am glad you got it to work!
>
>> Error budget - Well, I am within 5 ft on backtracked trails. Can't 
>> complain for working under a tree canopy.
>
> 1.8m isn't bad, at all!  Now: Imagine what happens when your typical 
> error is 2-3 meters, and a picnic table is smaller in at least one 
> dimension is smaller than the error budget.  The geometry is, well, 
> interesting, and usually looks more like a bow-tie than a rectangle. 
> Getting several points to define the radius of a trash can gets even 
> more entertaining.
>
>> I had the GPS unit on top of a 7 ft PVC pipe talking to my smartphone 
>> over bluetooth. I just ran out of time to cover the whole place but 
>> the proof of concept pans out.
>
> When I go do this stuff, I use a 2m "range" pole.  a fixed height 
> fiberglas and metal deal designed to poke holes in shoes and give one 
> a good feel that their antenna is exactly this high above the point in 
> question.  We also have a bulls-eye level on it to allow us to get it 
> spot-on above the point in question.
>
> Your rig sounds easier to work with.
>
> gerry
>
>> Now its off to other work tasks.
>>
>> 73 from 807,
>>
>> Richard, N6NKO
>>
>>
>> Gerry Creager wrote:
>>> Richard Polivka, N6NKO wrote:
>>>> Gerry,
>>>>
>>>> Good morning!
>>>>
>>>> I realize that wholeheartedly, but to have this big of a 
>>>> screwup....oh, wait, this is the Federal Government....
>>>
>>> Aha!  Your coffee kicked in?  What hardware are you using for your 
>>> campground survey?  I can tell you stories about those from several 
>>> years ago, when folks were trying to resolve objects (e.g., a picnic 
>>> table) that was smaller than their uncorrected L1 error budget...
>>>
>>> gerry
>>>
>>>> Gerry Creager wrote:
>>>>> Richard Polivka, N6NKO wrote:
>>>>>> I admit that one point does not make a trend but what I found was 
>>>>>> eyeopening.
>>>>>>
>>>>>> I wanted just Fond du Lac county in Wisconsin to use as a base 
>>>>>> map for mapping project that I am working on ( a Boy Scout 
>>>>>> campground). I pulled in my files into QGIS and then brought in  
>>>>>> "fe_2007_55039_edges". I did not get Fond du Lac County but a 
>>>>>> huge overview of north Illinois, Indiana and SE Michigan. OUCH!!!
>>>>>>
>>>>>> I even went and downloaded a virgin fileset and got the same 
>>>>>> results (see picture).
>>>>>>
>>>>>> 55039.png
>>>>>> This is not good. I plan on sending on a comment to the Census 
>>>>>> Bureau.
>>>>>>
>>>>>> So, let the user beware - YMMV.
>>>>>
>>>>> Unfortunately, this warning has always been necessary with TIGER 
>>>>> files.  They're not the best GIS data source.  They're just 
>>>>> available and free.
>>>> _______________________________________________
>>>> Xastir mailing list
>>>> Xastir at xastir.org
>>>> http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
>>>
>> _______________________________________________
>> Xastir mailing list
>> Xastir at xastir.org
>> http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
>