[mapserver-users] WMS: raster's x and y pixel dimension

Gerald Creager gerry.creager at tamu.edu
Tue Dec 1 17:57:56 EST 2009 

Jukka

The key issue here is that you should be making the WMS request, and 
thus, you know what the spatial extents, projection, and CRS are for 
that map.  If all you are doing is using a WMS result someone else got, 
without the key metadata, what you have is not a web _map_ but a 
picture.  If you've the metadata, you have a map processable via a GIS 
or suitable for use on another spatial display system such as MapServer.

gerry

Rahkonen Jukka wrote:
> Hi,
> 
> Thank you for clarifying my quick answer.  I am looking WCS from a narrow viewport because I use it mostly for delivering aerial images in original resolution and quality. WCS does give more. Delivering raw data is not the only alternative with WCS but it offers also some limited processing options like resampling to different resolution, reprojecting and a set of user selectable outputformats.
> When it comes to spatial relevance, for me the image captured from WMS does not have much spatial relevance after it has arrived to the computer if the request used for ordering it from the server is not known. GIS program who made the request does remember it but save it on a disk, or capture it with a web browser and it is just an image. Of course the situation is similar if you take an image from WCS server in png or jpeg format which do not carry embedded metadata. But this is not black and white either, Mapserver WMS can also create georeferenced geotiff or ecw files, even most WMS clients do not know what do do with them. Is it too simple to say that WMS was planned to be used for showing a map, WCS for downloading coverages and WFS for querying and downloading features?
> 
> -Jukka-
> 
> Gerald Creager wrote:
>  
> Er... not quite.
> 
> WMS is designed to provide a map for, say, a baselayer or background 
> with spatial relevance for GIS work.  A picture on a screen is similar, 
> but a WMS result has spatial relevance.
> 
> Web Coverage Service delivers a product with spatial relevance and data 
> embedded within the pixels, voxels, etc of the coverage.  You're not too 
> far off, but I believe you're attempting to oversimplify this.
> 
> A WFS result will provide a feature (line, polygon, point, polyline, 
> etc.) with all of its attributes.
> 
> In a coverage, e.g., a geotiff of a 3-band LandSAT image, you would have 
> information on which bands were provided for the RGB elements, and the 
> pixel values for each.  The coverage is georegistered so that the 
> spatial relevance of the "image" is preserved.  Similarly, a netcdf with 
> significantly more values could be passed as a coverage and utilized, 
> not limited to simply 3 "bands" of "color" (data).
> 
> gerry
> 
> Rahkonen Jukka wrote:
>> Hi,
>>
>> I would say that the main difference is that WMS is meant for showing a map on a computer screen, while WCS is made for letting users to download data so they can utilise it locally or process further.  Real life is not so black and white.  I promise you will find lots of good reading about WMS and WCS easily.  Do not forget to read a little bit about WFS as well, service for downloading vector data.
>>
>> -Jukka Rahkonen-
>>
>>
>> fla83tn wrote:
>>
>> Lähetetty: ti 1.12.2009 17:31
>> Vastaanottaja: Rahkonen Jukka; mapserver-users at lists.osgeo.org
>> Aihe: Re: Re: [mapserver-users] WMS: raster's x and y pixel dimension
>>  
>> Thank you Jukka for the quick reply. Now I'm able to correctly generate z-
>> dimension from DEM layer.
>> However, since I'm new to GIS, I'm not able to 
>> understand the differences between WCS and WMS..could 
>> you briefly summarize 
>> the goal of the two approach?
>> And, as last question , should I set the resX and 
>> resY parameters from client or could I embed them directly into the map file?
>>
>>
>> Best regards, 
>> Flavio
>>
>>> Hi,
>>>
>>> Width, height and BBOX are all compulsory 
>> parameters in WMS GetMap
>>> request and Mapserver is sending an image according 
>> to the request.  If
>>> you want to be able to control the pixel size easily, 
>> without making WMS
>>> client to balance the BBOX and image size in pixels, 
>> consider using WCS.
>>> One way to make a WCS request is 
>>>
>>> http://server.fi/cgi-
>> bin/mapserver_wcs?SERVICE=WCS&VERSION=1.0.0&REQUEST
>>
>>> =GetCoverage&COVERAGE=DEM&FORMAT=image/tiff&CRS=EPSG:3067&ResX=1.0&ResY=
>>> 1.
>> 0&BBOX=533652,6973434,534658,6974219
>>> You can see parameters ResX and ResY 
>> which are used for controlling the
>>> pixel size.
>>>
>>> -Jukka Rahkonen-
>>>
>>> fla83tn 
>> wrote:
>>>> Hi to all,
>>>> I've a problem with the loading of  a raster 
>> image via WMS (1.3.0).
>>>> To load the layers of my project I use gvSIG. If 
>> I load my 
>>>> digital elevation model (DEM) directly from filesystem (which 
>>>>
>> is a HFA/Erdas Image file - .img), 
>>>> x and y pixel dimension are fixed to 
>> 2.5 and -2.5 meters 
>>>> respectively, and fixed are also the width and height 
>> attributes.
>>>> If I load the layer from
>>>> Mapserver's WMS instead, x and y 
>> pixel dimension change as I 
>>>> zoom in or out (i.
>>>> e. changing the width
>>>>
>> and height parameters of the getMap request). 
>>>> Is there
>>>> the possibility 
>> to tell the wms client that x and y pixel 
>>>> dimension are constant and should 
>> never be calculated?
>>>> Here's my layer definition and the
>>>> tiff 
>> outputformat definition:
>>>> OUTPUTFORMAT
>>>>   NAME GTiff
>>>>   DRIVER 
>> "GDAL/GTiff"
>>>>   MIMETYPE "image/tiff"
>>>>   IMAGEMODE FLOAT32
>>>>   
>> EXTENSION "tif"
>>>> END
>>>>
>>>> LAYER
>>>>   NAME
>>>> "my_dem"
>>>>   EXTENT 669913.75 
>> 5143998.75 678313.75 5150701.25
>>>> 	
>>>>   METADATA
>>>>     
>>>> "wms_title"    
>> "my_dem"   ##required
>>>>     "wms_extent" "669913.75 5143998.75
>>>> 678313.75 
>> 5150701.25"
>>>>     "gml_include_items" "all"
>>>>   END
>>>>   TYPE RASTER
>>>>   
>>>>
>> STATUS ON
>>>>   PROJECTION
>>>>          "init=epsg:25832"
>>>>   END  
>>>>
>>>>   
>> DATA "my_dem.tiff"
>>>>   PROCESSING "NODATA=-9999"
>>>>   PROCESSING 
>> "SCALE=227.23,1741.15"
>>>>   PROCESSING
>>>> "SCALE_BUCKETS=2000"
>>>>   PROCESSING 
>> "BANDS=1"
>>>>   
>>>>   DEBUG on
>>>>   DUMP 	true
>>>>   
>>>> TEMPLATE "void" # enable 
>> queryable attribute on the layer END
>>>> Any help is
>>>> appreciated,
>>>>
>> Flavio
>>>> _______________________________________________
>>>> mapserver-users 
>> mailing list
>>>> mapserver-users at lists.osgeo.org
>>>> http://lists.osgeo.
>> org/mailman/listinfo/mapserver-users
>>
>>
>>
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> 
>

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