[MAPSERVER-USERS] Displaying population density with Mapserver

Thu May 29 00:50:55 PDT 2008

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
> >> >
> >> >
> >> >
> >>
> >> --
> >> View this message in context:
> >> http://www.nabble.com/Displaying-population-density-with-Mapserver-tp
> >> 17492210p17492387.html
> >> Sent from the Mapserver - User mailing list archive at Nabble.com.
> >>
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> >>
> >
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>
> --
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>
> 92210p17492783.html
>
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>
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