[MAPSERVER-USERS] Displaying population density with Mapserver

Thu May 29 09:47:23 EDT 2008

MapServer should do the conversion on the fly, my point was just that
MapServer needs to know what SRS (and units) that the data is in, so it
can make the translation.  

Can you post the text of your map file?  

David.

	-----Original Message-----
	From: Pierre-Benoit Besse [mailto:besse.pb at gmail.com] 
	Sent: Thursday, May 29, 2008 2:51 AM
	To: Fawcett, David
	Cc: mapserver-users at lists.osgeo.org
	Subject: Re: [MAPSERVER-USERS] Displaying population density
with Mapserver

	Hi David,

	I tried WGS84 yesterday after a little research on projection,
but it didn't change anything.
	I tried re-generating the shapefile with WGS84 projection but
it's still the same.
	In fact, my data comes from GPW v3
(http://sedac.ciesin.columbia.edu/gpw/global.jsp) but I didn't find any
clue on the projection used, I suppose there is none as you say.

	When you speak about translating ground units, do you mean I
have to translate my shapefile from degrees to, say, kilometers before I
can use SIZEUNITS kilometers ? I thought it could be done dynamically by
MapServer.
	I found a tutorial about this, I will try it anyway (assuming my
data is WGS84) and give you the outcome :)

	I attached my mapfile this time, just in case I made a noob
mistake somewhere...

	thank you very much !

	Faldor

	2008/5/28 Fawcett, David <David.Fawcett at state.mn.us>:

		Faldor,

		When you have point coordinates stored in a text file,
there really is
		no way to encode/attach the projection definition.  Even
if you could,
		it doesn't sound like you really know what spatial
reference system
		(SRS) or projection that it is in.  The key to
projecting to another SRS
		or translating ground units to another measure (from
degrees to meters)
		is knowing what the current SRS of the data is.

		Since your data is worldwide and it is unprojected
(lat/lon), a good
		first guess would be to assume that it is unprojected
with using the
		WGS84.

		Try defining your layer projection by including this
block in your layer
		definition.

		PROJECTION
		  "init=epsg:4326"
		END

		David.

		-----Original Message-----
		From: mapserver-users-bounces at lists.osgeo.org
		[mailto:mapserver-users-bounces at lists.osgeo.org] On
Behalf Of

		Pierre-Benoit Besse
		Sent: Wednesday, May 28, 2008 4:11 AM
		To: Fawcett, David

		Cc: mapserver-users at lists.osgeo.org
		Subject: Re: [MAPSERVER-USERS] Displaying population
density with
		Mapserver

		Well, I confess, I'm new to GIS applications and I do
not know a lot
		about projections.
		I understand I have to tell MapServer what is the
projection of each
		layer I use in the mapfile, but using ogrinfo on my
shapefiles tells me
		that :

		Layer name: pop_density
		Geometry: Point
		Feature Count: 249937
		Extent: (-180.000000, -56.000000) - (179.750000,
83.500000)
		Layer SRS WKT:
		(unknown)
		latitude: Real (24.15)
		longitude: Real (24.15)
		densite: Real (24.15)

		I generated this shapefile from a CSV file with 3
columns : latitude,
		longitude, density_value.
		Did I have to define a projection then ? How do I do
that ?

		Best regards,

		Faldor

		2008/5/27 Fawcett, David <David.Fawcett at state.mn.us>:

		Have you defined an output projection for your map and
input projections
		for each of your layers?  It is likely that MapServer
needs to know what
		the input projection/SRS is before it can translate to
different units.

		David.
		-----Original Message-----
		From: Pierre-Benoit Besse [mailto:besse.pb at gmail.com]
		Sent: Tuesday, May 27, 2008 11:26 AM
		To: Fawcett, David
		Cc: Ritesh Ambastha; mapserver-users at lists.osgeo.org
		Subject: Re: [MAPSERVER-USERS] Displaying population
density with
		Mapserver

		Ha, well, I prefer that :) I would need a lot of layer
definitions to
		obtain something ok...

		But I just tried the "ground units" stuff, I tried with
a 50 kilometers
		wide square and it drew squares the size of ASIA !! oO
		I had to define a 1 feet wide square to obtain something
more or less
		ok...
		Does anybody know why ?

		Aside from that It seems to work, thank you !

		I will try the scalesymbol stuff tomorrow.

		Regards

		2008/5/27 Fawcett, David <David.Fawcett at state.mn.us>:

		Before you create lots of different layers to simulate
symbol scaling,
		you may want to try something else.  It has been a long
time since I
		have played with scaled symbols, but give it a try.

		You should be able to scale the symbols by setting a
SYMBOLSCALE in the
		LAYER object.  This is the scale at which you want the
symbol to appear
		at the SIZE stated in the map file.

		You may want to modify STYLE MAXSIZE if you think that
you will want
		your symbols to be larger than 50 pixels.

		Another completely different approach that just came to
my mind would be
		to use ground units (e.g. meters) to set the size of
your symbol.  To do
		this, set LAYER SIZEUNITS to meters.  Calculate the size
of a symbol in
		meters on the ground that will touch adjacent symbols,
or give you the
		desired amount of space between the symbols.  That way,
the symbols
		should scale consistently.

		David.

		-----Original Message-----
		From: mapserver-users-bounces at lists.osgeo.org

		[mailto:mapserver-users-bounces at lists.osgeo.org] On
Behalf Of Ritesh
		Ambastha
		Sent: Tuesday, May 27, 2008 10:16 AM
		To: mapserver-users at lists.osgeo.org
		Subject: Re: [MAPSERVER-USERS] Displaying population
density with
		Mapserver

		Dear Faldor,

		Robert is absolutely right. You will have to make
different LAYERS for
		the same POINT layer. But, define MAX/MINSCALE for each
Layer. Change
		STYLE -> SIZE values in each of the layer. You are done
!!

		Cheers !
		Ambastha

		Faldor wrote:
		>
		> Yes, but I need them to adapt for different extents.
		>
		> For example, When I zoom out enough to see the world,
I need them 1
		> pixel wide (it's ugly otherwise), but when I zoom in I
will need then
		> 2 or 5 or even 30 pixels wide to cover all space.
		>
		> 2008/5/27 Ritesh Ambastha <group.ritesh at gmail.com>:
		>
		>>
		>> Dear Faldor,
		>>
		>> <snip>What I need is to have the points grow to cover
all space
		>> available when I zoom in.</snip>
		>>
		>> Do you mean that the size of points should grow? It
can be done
		>> easily by setting proper SIZE in the STYLE tag.
		>>
		>>
		>> Regards,
		>> Ambastha
		>>
		>>
		>>
		>> Faldor wrote:
		>> >
		>> > Hi,
		>> >
		>> > Sorry for my first empty message.
		>> >
		>> > My problem is, I need to display population density
with Mapserver.

		>> > The data comes from GPWv3 and has a resolution of
15'. I converted
		>> > it to a POINT Shapefile using ogr2ogr.
		>> >
		>> > At first when I display it on a world map it shows
nicely. But when

		>> > I
		>> zoom
		>> > in it begins to show separated points for each
value in the
		>> > shapefile. What I need is to have the points grow
to cover all
		>> > space available
		>> when
		>> I
		>> > zoom in.
		>> >
		>> > Is there any mean to do it with Mapserver ? I did
not find it in
		>> > the mapfile reference.
		>> >
		>> > I don't know if I explained it well (I'm not
english speaking). If
		>> > you
		>> do
		>> > not understand something, please ask.
		>> >
		>> > Cordialy,
		>> >
		>> > Faldor
		>> >
		>> >
		>> >
		>>
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		>> 17492210p17492387.html
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at Nabble.com.
		>>
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