[MAPSERVER-USERS] Displaying population density with Mapserver

Thu May 29 10:50:55 EDT 2008

ALRIGHT !!

It was a noob mistake indeed, I did not specify UNITS in the MAP object. In
fact I thought Mapserver could know it from the shapefile.

Thank you very much, it works fine now :)

Faldor

2008/5/29 Fawcett, David <David.Fawcett at state.mn.us>:

>  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
>> >> >
>> >> >
>> >> >
>> >>
>> >> --
>> >> View this message in context:
>> >> http://www.nabble.com/Displaying-population-density-with-Mapserver-tp
>> >> 17492210p17492387.html
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>> >>
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>> 92210p17492783.html
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