| Re: Overlay images from WMS servers (web mapping servers) on map projections [message #47424 is a reply to message #47422] |
Wed, 08 February 2006 11:55   |
Jan Kristian Jensen
Messages: 10
Registered: February 2006
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Junior Member |
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David Fanning wrote:
> Jan Kristian Jensen writes:
>> map_set, 0, 0, /cylindrical, xmargin = 0, ymargin = 0, limit = limit
>
>
> Whenever I've had to solve this problem, I use POSITION-[0,0,1,1]
> instead if the [XY]Margin keywords. I'd try that and see
> if it helps.
Nope - same problem as before. At least the /noborder, x/ymargin and
position seems to behave consistently (but maybe not the way I hope for)
Also, and probably more importantly, I would
> make sure your latcenter and loncenter are in the center
> of you limits. They aren't, currently.
I've played around with different values for p0Lat, p0Lon. Changing them
has no visible effect whatsoever - at least not at this scale. The
mismatch looks about the same.
From this group I understand that setting p0Lat, p0lon correctly often
is crucial, probably because many projection demands that you specify
some point of origin (central meridian or similar) for your map. This
particular projection demands that the central meridian is zero, hence
p0lat = 0.
The EPSG:4326 is probably the simplest projection available, and has
many names: Equidistant lat/lon grid, equirectangular, rectangular
projection, plane chart, plate carre, unprojected map, lat/lon grid...
More formally, epsg:4326 is a special case of a cylindrical projection,
defined by that the central meridian is zero.
http://mathworld.wolfram.com/EquirectangularProjection.html
According to the docs, this is the _*/default\*_ projection used by
map_set - and p0Lat, p0lon = 0 is the default value for these optional
parameters.
Jan
--
Jan Kristian Jensen
Remove the obvious from the email adress to email me.
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