shrug-l: Question du jour

Sykes, John John.Sykes@dep.state.fl.us
Fri, 30 Sep 2005 12:41:11 -0400


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That's a good website.  From it I gather that if I want BOTH the =
distances
and azimuths to my sampling locations from the site center to be the =
most
accurate, the Azimuthal Equidistant projection is the best solution.
=20
I came up with part of the rest of your solution on my own, however, I'm
having trouble rotating it through 360=B0.
=20
Another solution I thought of, is setting up the sector lines in an =
AutoCad
file, then importing it into my map with a world file using the center =
point
and the intersection of the first radial with the 10 mile buffer ring as =
the
two points.

-- John=20

=20

  _____ =20

From: Geographic Systems LLC [mailto:info@geographicsystems.com]=20
Sent: Friday, September 30, 2005 12:19 PM
To: Sykes, John
Subject: RE: shrug-l: Question du jour



Hi John,

=20

I will try to address the first part of your question (drawing lines out =
10
miles at 11.25 degree increments) and the last part (projections).  The
second part of your question (rhumb line from site point to sampling
location) may require more research.

=20

Projections - definitely play a part in spatial accuarcy.  My guess is =
you
want a projection that preserves direction and distance.  A good place =
to
start is the summary tables at the bottom of the map projection poster,
http://erg.usgs.gov/isb/pubs/MapProjections/projections.html.=20

=20

Drawing lines of specific distance and angle.  You can do this manually =
when
you sketch a line.  With Task set to Create New Feature and Target your =
line
feature class, click the sketch tool (pencil) and click on the first =
point of
your line.  Then right click away from the sketch and select "Direction" =
(or
CTRL-A) specify an angle (0 being horizontal - ie "11.25") and then =
right
click away from sketch again and select "Length" (or CTRL-L) ie "2mi" =
("mi"
for miles).  Or you can enter both the first time you right click by
selecting "Direction/Length" (or CTRL-G).  Check out online help for
"Creating segments using angles and lengths".

=20

Miguel Garriga

Geographic Systems, LLC

www.geographicsystems.com

407-261-0451

cel 321-279-6019

  _____ =20

From: shrug-l-admin@lists.dep.state.fl.us
[mailto:shrug-l-admin@lists.dep.state.fl.us] On Behalf Of Sykes, John
Sent: Friday, September 30, 2005 10:21 AM
To: shrug-L@lists.dep.state.fl.us
Subject: shrug-l: Question du jour

=20

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

Problem=20

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=20

*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.


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<DIV dir=3Dltr align=3Dleft><FONT face=3DArial color=3D#0000ff =
size=3D4><SPAN=20
class=3D093303416-30092005>That's a good website.&nbsp; From it I gather =
that if I=20
want BOTH the distances and azimuths to my sampling locations from the =
site=20
center to be the most accurate, the Azimuthal Equidistant projection is =
the best=20
solution.</SPAN></FONT></DIV>
<DIV dir=3Dltr align=3Dleft><FONT face=3DArial color=3D#0000ff =
size=3D4><SPAN=20
class=3D093303416-30092005></SPAN></FONT>&nbsp;</DIV>
<DIV dir=3Dltr align=3Dleft><FONT face=3DArial color=3D#0000ff =
size=3D4><SPAN=20
class=3D093303416-30092005>I came up with part of the rest of your =
solution on my=20
own, however, I'm having trouble rotating it through =
360=B0.</SPAN></FONT></DIV>
<DIV dir=3Dltr align=3Dleft><FONT face=3DArial color=3D#0000ff =
size=3D4><SPAN=20
class=3D093303416-30092005></SPAN></FONT>&nbsp;</DIV>
<DIV dir=3Dltr align=3Dleft><FONT face=3DArial color=3D#0000ff =
size=3D4><SPAN=20
class=3D093303416-30092005>Another solution I thought of, is setting up =
the sector=20
lines in an AutoCad file, then importing it into my map with a world =
file using=20
the center point and the intersection of the first radial with the 10 =
mile=20
buffer ring as the two points.</SPAN></FONT></DIV>
<P><B><FONT face=3D"Monotype Corsiva" size=3D5>-- John</FONT></B> </P>
<DIV>&nbsp;</DIV><BR>
<DIV class=3DOutlookMessageHeader lang=3Den-us dir=3Dltr align=3Dleft>
<HR tabIndex=3D-1>
<FONT face=3DTahoma size=3D2><B>From:</B> Geographic Systems LLC=20
[mailto:info@geographicsystems.com] <BR><B>Sent:</B> Friday, September =
30, 2005=20
12:19 PM<BR><B>To:</B> Sykes, John<BR><B>Subject:</B> RE: shrug-l: =
Question du=20
jour<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV class=3DSection1>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Hi=20
John,<o:p></o:p></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"><o:p>&nbsp;</o:p></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">I will try to =
address=20
the first part of your question (drawing lines out 10 miles at 11.25 =
degree=20
increments) and the last part (projections). &nbsp;The second part of =
your=20
question (rhumb line from site point to sampling location) may require =
more=20
research.<o:p></o:p></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"><o:p>&nbsp;</o:p></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Projections =
=96=20
definitely play a part in spatial accuarcy. &nbsp;My guess is you want a =

projection that preserves direction and distance.&nbsp; A good place to =
start is=20
the summary tables at the bottom of the map projection poster, <A=20
href=3D"http://erg.usgs.gov/isb/pubs/MapProjections/projections.html">htt=
p://erg.usgs.gov/isb/pubs/MapProjections/projections.html</A>.=20
<o:p></o:p></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"><o:p>&nbsp;</o:p></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Drawing lines =
of=20
specific distance and angle. &nbsp;You can do this manually when you =
sketch a=20
line. &nbsp;With Task set to Create New Feature and Target your line =
feature=20
class, click the sketch tool (pencil) and click on the first point of =
your=20
line.&nbsp; Then right click away from the sketch and select =
=93Direction=94 (or=20
CTRL-A) specify an angle (0 being horizontal =96 ie =9311.25=94) and =
then right click=20
away from sketch again and select =93Length=94 (or CTRL-L) ie =932mi=94 =
(=93mi=94 for=20
miles). &nbsp;Or you can enter both the first time you right click by =
selecting=20
=93Direction/Length=94 (or CTRL-G).&nbsp; Check out online help for =
=93Creating=20
segments using angles and lengths=94.<o:p></o:p></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial"><o:p>&nbsp;</o:p></SPAN></FONT></P>
<DIV>
<DIV>
<P class=3DMsoNormal><EM><I><FONT face=3DArial color=3Dnavy =
size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Miguel=20
Garriga</SPAN></FONT></I></EM><FONT color=3Dnavy><SPAN=20
style=3D"COLOR: navy"><o:p></o:p></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Geographic =
Systems,=20
LLC</SPAN></FONT><FONT color=3Dnavy><SPAN=20
style=3D"COLOR: navy"><o:p></o:p></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"><A=20
href=3D"http://www.geographicsystems.com">www.geographicsystems.com</A></=
SPAN></FONT><FONT=20
color=3Dnavy><SPAN style=3D"COLOR: navy"><o:p></o:p></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: =
Arial">407-261-0451</SPAN></FONT><FONT=20
color=3Dnavy><SPAN style=3D"COLOR: navy"><o:p></o:p></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">cel=20
321-279-6019</SPAN></FONT><o:p></o:p></P></DIV></DIV>
<DIV>
<DIV class=3DMsoNormal style=3D"TEXT-ALIGN: center" align=3Dcenter><FONT =

face=3D"Times New Roman" size=3D3><SPAN style=3D"FONT-SIZE: 12pt">
<HR tabIndex=3D-1 align=3Dcenter width=3D"100%" SIZE=3D2>
</SPAN></FONT></DIV>
<P class=3DMsoNormal><B><FONT face=3DTahoma size=3D2><SPAN=20
style=3D"FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: =
Tahoma">From:</SPAN></FONT></B><FONT=20
face=3DTahoma size=3D2><SPAN style=3D"FONT-SIZE: 10pt; FONT-FAMILY: =
Tahoma">=20
shrug-l-admin@lists.dep.state.fl.us =
[mailto:shrug-l-admin@lists.dep.state.fl.us]=20
<B><SPAN style=3D"FONT-WEIGHT: bold">On Behalf Of </SPAN></B>Sykes,=20
John<BR><B><SPAN style=3D"FONT-WEIGHT: bold">Sent:</SPAN></B> Friday, =
September=20
30, 2005 10:21 AM<BR><B><SPAN style=3D"FONT-WEIGHT: bold">To:</SPAN></B> =

shrug-L@lists.dep.state.fl.us<BR><B><SPAN=20
style=3D"FONT-WEIGHT: bold">Subject:</SPAN></B> shrug-l: Question du=20
jour</SPAN></FONT><o:p></o:p></P></DIV>
<P class=3DMsoNormal><FONT face=3D"Times New Roman" size=3D3><SPAN=20
style=3D"FONT-SIZE: 12pt"><o:p>&nbsp;</o:p></SPAN></FONT></P>
<P><FONT face=3DArial size=3D4><SPAN=20
style=3D"FONT-SIZE: 13.5pt; FONT-FAMILY: Arial">Since we (collectively) =
solved the=20
question I had yesterday, here's a new one (put on your thinking caps - =
this=20
one's tougher!).</SPAN></FONT><o:p></o:p></P>
<P><FONT face=3DArial size=3D4><SPAN=20
style=3D"FONT-SIZE: 13.5pt; FONT-FAMILY: Arial">Problem</SPAN></FONT>=20
<o:p></o:p></P>
<P><FONT face=3DArial size=3D4><SPAN=20
style=3D"FONT-SIZE: 13.5pt; FONT-FAMILY: Arial">When establishing =
environmental=20
sampling locations around a site, we like to ensure that the various =
distance=20
buffer rings are evenly covered (e.g., in this case:&nbsp; "site =
boundary" to 2=20
miles, 2 - 5 miles and 5 - 10 miles.&nbsp; This is simple to create and =
check=20
with the standard multiple buffer tool in=20
ArcToolbox.</SPAN></FONT><o:p></o:p></P>
<P><FONT face=3DArial size=3D4><SPAN=20
style=3D"FONT-SIZE: 13.5pt; FONT-FAMILY: Arial">However, we also like to =
check=20
that the 16 compass sectors around the site have also been evenly=20
covered*.&nbsp; These 22-1/2=B0 sectors are centered on N, NNE, NE, ENE, =
E, ESE,=20
SE, SSE, S, SSW, SW, WSW, W, WNW, NW and =
NNW.</SPAN></FONT><o:p></o:p></P>
<P><FONT face=3DArial size=3D4><SPAN=20
style=3D"FONT-SIZE: 13.5pt; FONT-FAMILY: Arial">So, what I would like to =
do is to=20
create these sectors visually, by drawing a line from the origin (an =
arbitrary=20
"center" point on the site) out to 10 miles starting at 11-1/4=B0 =
compass heading,=20
then rotate around 22-1/2=B0 and draw a line, until the 16 sectors are =
visually=20
defined.</SPAN></FONT><o:p></o:p></P>
<P><FONT face=3DArial size=3D4><SPAN=20
style=3D"FONT-SIZE: 13.5pt; FONT-FAMILY: Arial">Any suggestions as how =
this can be=20
done (easily)?&nbsp; Previously, when doing this in AutoCad, I used a =
radial=20
copy command.&nbsp; I haven't noticed a similar command in=20
ArcGIS.</SPAN></FONT><o:p></o:p></P>
<P><FONT face=3DArial size=3D4><SPAN=20
style=3D"FONT-SIZE: 13.5pt; FONT-FAMILY: Arial">Finally, once the =
sampling=20
location is selected (and the lat/long of that location determined), we =
need to=20
be able to determine and list the distance and azimuth (rhumb line) from =
that=20
arbitrary "center" point on the site to the sampling location and put it =
into=20
the sampling location attributes table (in the past, I've done this =
using the=20
NGS "Inverse" program [fudging the rhumb line from the great circle =
azimuths]=20
using a batch file input/output) for atmospheric dispersion =
modeling.&nbsp;=20
However, I don't see any easy way to do this with ArcInfo (especially on =
a batch=20
file basis).&nbsp; Any suggestions?</SPAN></FONT><o:p></o:p></P>
<P><FONT face=3DArial size=3D4><SPAN=20
style=3D"FONT-SIZE: 13.5pt; FONT-FAMILY: Arial">Finally, food for =
thought -- How=20
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=20
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=20
these functions may be rather =
projection-sensitive.</SPAN></FONT><o:p></o:p></P>
<P><B><FONT face=3D"Monotype Corsiva" size=3D5><SPAN=20
style=3D"FONT-WEIGHT: bold; FONT-SIZE: 18pt; FONT-FAMILY: 'Monotype =
Corsiva'">--=20
John</SPAN></FONT></B> <o:p></o:p></P>
<P><FONT face=3DArial size=3D4><SPAN=20
style=3D"FONT-SIZE: 13.5pt; FONT-FAMILY: Arial">*Sometimes if there is a =

prevailing wind bias, we'll bias our sampling locations to that =
prevailing wind=20
direction, but in the current case there is no strong prevailing wind =
direction=20
- the annual wind rose shows an almost random=20
360=B0pattern.</SPAN></FONT><o:p></o:p></P></DIV></BODY></HTML>

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