shrug-l: Question du jour

Sykes, John John.Sykes@dep.state.fl.us
Fri, 30 Sep 2005 10:20:49 -0400


This is a multi-part message in MIME format.

------_=_NextPart_001_01C5C5CA.2846CB41
Content-Type: text/plain;
	charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable

Since we (collectively) solved the question I had yesterday, here's a =
new one
(put on your thinking caps - this one's tougher!).

Problem

When establishing environmental sampling locations around a site, we =
like to
ensure that the various distance buffer rings are evenly covered (e.g., =
in
this case:  "site boundary" to 2 miles, 2 - 5 miles and 5 - 10 miles.  =
This
is simple to create and check with the standard multiple buffer tool in
ArcToolbox.

However, we also like to check that the 16 compass sectors around the =
site
have also been evenly covered*.  These 22-1/2=B0 sectors are centered on =
N,
NNE, NE, ENE, E, ESE, SE, SSE, S, SSW, SW, WSW, W, WNW, NW and NNW.

So, what I would like to do is to create these sectors visually, by =
drawing a
line from the origin (an arbitrary "center" point on the site) out to 10
miles starting at 11-1/4=B0 compass heading, then rotate around =
22-1/2=B0 and
draw a line, until the 16 sectors are visually defined.

Any suggestions as how this can be done (easily)?  Previously, when =
doing
this in AutoCad, I used a radial copy command.  I haven't noticed a =
similar
command in ArcGIS.

Finally, once the sampling location is selected (and the lat/long of =
that
location determined), we need to be able to determine and list the =
distance
and azimuth (rhumb line) from that arbitrary "center" point on the site =
to
the sampling location and put it into the sampling location attributes =
table
(in the past, I've done this using the NGS "Inverse" program [fudging =
the
rhumb line from the great circle azimuths] using a batch file =
input/output)
for atmospheric dispersion modeling.  However, I don't see any easy way =
to do
this with ArcInfo (especially on a batch file basis).  Any suggestions?

Finally, food for thought -- How does the projection being used effect =
the
accuracy of all of this?  Normally we use Albers (equal area) or =
Mercator
(which gives the most accurate rhumb lines), but is there a better =
projection
to use to obtain accurate distances & azimuths?  I understand from the
reading I've done that these functions may be rather =
projection-sensitive.

-- John

*Sometimes if there is a prevailing wind bias, we'll bias our sampling
locations to that prevailing wind direction, but in the current case =
there is
no strong prevailing wind direction - the annual wind rose shows an =
almost
random 360=B0pattern.

------_=_NextPart_001_01C5C5CA.2846CB41
Content-Type: text/html;
	charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<HTML>
<HEAD>
<META HTTP-EQUIV=3D"Content-Type" CONTENT=3D"text/html; =
charset=3Diso-8859-1">
<META NAME=3D"Generator" CONTENT=3D"MS Exchange Server version =
6.0.6603.0">
<TITLE>Question du jour</TITLE>
</HEAD>
<BODY>
<!-- Converted from text/rtf format -->

<P><FONT SIZE=3D4 FACE=3D"Arial">Since we (collectively) solved the =
question I had yesterday, here's a new one (put on your thinking caps - =
this one's tougher!).</FONT></P>

<P><FONT SIZE=3D4 FACE=3D"Arial">Problem</FONT>
</P>

<P><FONT SIZE=3D4 FACE=3D"Arial">When establishing environmental =
sampling locations around a site, we like to ensure that the various =
distance buffer rings are evenly covered (e.g., in this case:&nbsp; =
&quot;site boundary&quot; to 2 miles, 2 - 5 miles and 5 - 10 =
miles.&nbsp; This is simple to create and check with the standard =
multiple buffer tool in ArcToolbox.</FONT></P>

<P><FONT SIZE=3D4 FACE=3D"Arial">However, we also like to check that the =
16 compass sectors around the site have also been evenly covered*.&nbsp; =
These 22-1/2=B0 sectors are centered on N, NNE, NE, ENE, E, ESE, SE, =
SSE, S, SSW, SW, WSW, W, WNW, NW and NNW.</FONT></P>

<P><FONT SIZE=3D4 FACE=3D"Arial">So, what I would like to do is to =
create these sectors visually, by drawing a line from the origin (an =
arbitrary &quot;center&quot; point on the site) out to 10 miles starting =
at 11-1/4=B0 compass heading, then rotate around 22-1/2=B0 and draw a =
line, until the 16 sectors are visually defined.</FONT></P>

<P><FONT SIZE=3D4 FACE=3D"Arial">Any suggestions as how this can be done =
(easily)?&nbsp; Previously, when doing this in AutoCad, I used a radial =
copy command.&nbsp; I haven't noticed a similar command in =
ArcGIS.</FONT></P>

<P><FONT SIZE=3D4 FACE=3D"Arial">Finally, once the sampling location is =
selected (and the lat/long of that location determined), we need to be =
able to determine and list the distance and azimuth (rhumb line) from =
that arbitrary &quot;center&quot; point on the site to the sampling =
location and put it into the sampling location attributes table (in the =
past, I've done this using the NGS &quot;Inverse&quot; program [fudging =
the rhumb line from the great circle azimuths] using a batch file =
input/output) for atmospheric dispersion modeling.&nbsp; However, I =
don't see any easy way to do this with ArcInfo (especially on a batch =
file basis).&nbsp; Any suggestions?</FONT></P>

<P><FONT SIZE=3D4 FACE=3D"Arial">Finally, food for thought -- How does =
the projection being used effect the accuracy of all of this?&nbsp; =
Normally we use Albers (equal area) or Mercator (which gives the most =
accurate rhumb lines), but is there a better projection to use to obtain =
accurate distances &amp; azimuths?&nbsp; I understand from the reading =
I've done that these functions may be rather =
projection-sensitive.</FONT></P>

<P><B><FONT SIZE=3D5 FACE=3D"Monotype Corsiva">-- John</FONT></B>
</P>

<P><FONT SIZE=3D4 FACE=3D"Arial">*Sometimes if there is a prevailing =
wind bias, we'll bias our sampling locations to that prevailing wind =
direction, but in the current case there is no strong prevailing wind =
direction - the annual wind rose shows an almost random =
360=B0pattern.</FONT></P>

</BODY>
</HTML>
------_=_NextPart_001_01C5C5CA.2846CB41--