[texbirds] Re: Count Circle and CBC centers

  • From: "Bartels, Keith A." <keith.bartels@xxxxxxxx>
  • To: "david@xxxxxxxxxxx" <david@xxxxxxxxxxx>, TexBirds <texbirds@xxxxxxxxxxxxx>
  • Date: Mon, 25 Nov 2013 16:11:44 +0000

I think I may have posted this in the past, but maybe not here.  For a CBC 
circle, the earth is essentially flat.  If you go through the geometry, the 
error in the CBC circle radius due to the earth's curvature is about 0.5 
inches. 7.5 miles vs. 7.500008789 miles.  So being off by 0.25 miles must be 
for another reason.

Keith

-----Original Message-----
From: texbirds-bounce@xxxxxxxxxxxxx [mailto:texbirds-bounce@xxxxxxxxxxxxx] On 
Behalf Of David Sarkozi
Sent: Saturday, November 23, 2013 7:49 AM
To: jjones4fwas@xxxxxxxxx
Cc: TexBirds
Subject: [texbirds] Re: Count Circle and CBC centers

Jim a consideration in a paper map count circle is a circle on a map is only a 
circle when the map projection is a great circle projection centered on the 
center of the count circle. I did some checking with a gps that gave me the 
distance to a landmark set on the physical description of the count circle. In 
this case the center was something I could walk right up to so I know my center 
was 100% accurate. I found even though I has a USGS map with the radius drawn 
properly, the gps showed that by edges were off by as much as a quarter mile. 
In my case it made very little difference, but there are cases where something 
areas are counted at the very edge of a circle and it could be a big deal.
I know the Bolivar Penn Count circle coordinates on the NAS websites are 
incorrect, they show most of the circle in the Gulf of mexico, when only about 
a mile of the Gulf is actually in the circle. When I took over compiling that 
count, sent in a correction but it doesn't appear to actually have "stuck" I 
have matched up the physical description with landmarks on the edges of the 
circle that Bill Graber gave me that he used to draw the original map and they 
match up well, but I chalk the error in the coordinates to maps 50 years ago 
just weren't as easy to use as Google Earth is today.


On Thu, Nov 21, 2013 at 4:06 PM, JimJones-FWAS <jjones4fwas@xxxxxxxxx>wrote:

> I felt that I needed to address two issues I have with some of the 
> comments about this App and the CBC data shown on the National Audubon 
> Society website.
> I do not have the App so it may in fact be a wonderful thing to 
> behold. But one of the replies on TexBirds said if you don't like 
> where your circle is, the APP allows you to submit a request to change 
> it. I sure hope that the App developers contact the local compilers before 
> doing any changes.
> Otherwise, the historical census in a well-established CBC becomes useless.
> My second issue is with the CBC map available on the NAS website. If 
> the App and the NAS data are interlinked, be aware of one glaring 
> error with the NAS map.
> I take part in two local CBCs in Fort Worth, the Fort Worth CBC and 
> Village Creek Drying Beds CBC. I looked at the NAS CBC map and saw 
> that the drawn circles did not extend out as far as the Topo map we've 
> used for many years.
> I measured both of the local circles on the NAS website and discovered 
> they are drawn at 12.6 miles in diameter!?! I also looked at and 
> measured five other CBC circles in north Texas. All are shown as 12.6 miles 
> in diameter.
> A
> CBC circle is to be 15-miles in diameter.
> If you use the NAS map or the App (if it has the same fault in its 
> design), be aware that you are losing over a full mile of the 
> outer-radius in your circle area.
> I agree with Bush's comment: know your area.
> I would add: if needed, go to the library and get a survey map that 
> includes your circle and draw the 15-mile circle onto it. If the 
> library can't make copies for you, write down the map number and hit 
> the internet. I collected these types of maps for many years. As 
> recently as 2003, I purchased them from various stores and government 
> agencies. Stores that specialize in hiking and other serious outdoor 
> activities usually have local maps available.
>
> Jim Jones
> Bedford, TX
>
>
>
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--
David Sarkozi
Houston, TX
(713) 412-4409 twitter ID dsarkozi


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