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<DIV dir=ltr align=left><SPAN class=278473211-29042011><FONT face=Arial
color=#0000ff size=2>Hi Dave,</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=278473211-29042011><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=278473211-29042011><FONT face=Arial
color=#0000ff size=2>You are certainly not on the right track, because the SRS
EPSG:4326 is not a projection system, but more a datum (WGS84), based on an
ellipsoid (GRS80). In a nutshell, the 4326 srs is a "spherical"
geographic system and that is why the unit of measurement is in
degree. So when you store your data in EPSG:4326, that means your data
will have to be stored in latitude and longitude, and you cannot represent
lat-long coordinates directly on a map, unless these coordinates are projected
in a cartesian (X and Y) coordinate system, like the Google Mercator
projection (EPSG:900913).</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=278473211-29042011><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=278473211-29042011><FONT face=Arial
color=#0000ff size=2>That said, you specified in your first mail that your were
working with "lines" measured in nautilcal miles, within a grid graduated for 0
to 100. That means that you are already in a "projected" coordinate
system. Now, we have to figure out what is this coordinate
system. Maybe I am wrong, but your 0-100 grid seems to
represent a cartesian coordinate system in GRAD (not in
degree)... </FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=278473211-29042011><FONT face=Arial
color=#0000ff size=2></FONT></SPAN><SPAN class=278473211-29042011><FONT
face=Arial color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=278473211-29042011></SPAN><FONT face=Arial><FONT
color=#0000ff><FONT size=2>C<SPAN class=278473211-29042011>ould you check and
confirm that at first? Also, a screenshot of your map would be
helpful...</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=278473211-29042011></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=278473211-29042011>Regards,</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=278473211-29042011></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=278473211-29042011>Marc-André</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=278473211-29042011></SPAN></FONT></FONT></FONT> </DIV>
<DIV><BR></DIV>
<DIV class=OutlookMessageHeader lang=fr dir=ltr align=left>
<HR tabIndex=-1>
<FONT face=Tahoma size=2><B>De :</B>
postgis-users-bounces@postgis.refractions.net
[mailto:postgis-users-bounces@postgis.refractions.net] <B>De la part de</B>
Dave<BR><B>Envoyé :</B> 29 avril 2011 04:05<BR><B>À :</B> PostGIS
Users Discussion<BR><B>Objet :</B> Re: [postgis-users] drawing nautical
data on projection 4326[solution?]<BR></FONT><BR></DIV>
<DIV></DIV>I think I have a solution to this issue<BR><BR>I am going to convert
my point origin to meter based projection (eg google 900913), create my line
data, then transform it back to the 4326 projection, in this way the scale
factors calculations should be done by the proj library.<BR><BR>Does this sound
like a decent solution?<BR><BR>On 28/04/2011 10:48, Dave wrote:
<BLOCKQUOTE cite=mid:4DB937FE.2050007@pinan.co.uk type="cite">I have some
line data measured in nautical miles.<BR><BR>I want to draw these points
on a map using the 4326 projection, the srs entry for this projection gives
the unit of measurement as degree.<BR><BR>A nautical mile is one minture of an
arc of lattitude ie 0-60, the projection is measured in 0-100.<BR><BR>So does
this mean that when I want to draw a line measured in nautical miles, I
have map 0-60 on to 0-100 grid , ie I have to apply 0.6 factor
?<BR><BR>So a line starting at lat 1.2 and ending at lat 2.7
becomes a line 1.12 to 2.42
?<BR><BR>regards<BR><BR><BR>Dave.<BR><BR><BR><PRE wrap=""><FIELDSET class=mimeAttachmentHeader></FIELDSET>
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