[mapserver-users] Output image resolution - explanation needed

[Steve Lime]

Resolution in MapServer-speak is referring to the resolution of the output device a map
will be displayed on. The value is used for scale computations and nothing else. It does not
affect the size (in pixels) of MapServer. Scale values do impact the size at which features
and text are rendered IF scaling (via SYMBOLSCALE) is turned on. Higher quality output is
usually a matter of having more pixels to print, however you usually want larger features
too which is where the resolution parameter combined with scaling can help.

Steve

>>> On 7/30/2008 at 2:21 AM, in message
<OF8A10F31F.0E3F1C94-ONC1257496.0026AB23-C1257496.00286464 at pula.hr>,
<Dejan.Gambin at pula.hr> wrote:
> Hi,
> 
> I am trying to download a high resolution image and print it on a paper. I 
> am using p.mapper and its download function that enables downloading the 
> map image on different resolutions. 
> 
> I have turned on my raster layer (ortophoto image). I have zoomed in to an 
> area of interest. I have downloaded the map twice - with a resolution of 
> 150 and 300. The image is shown i a new page/tab (firefox). I right click 
> on the image and save it as a png (also tried with a jpeg) file. Now, the 
> first file is 2150x1111 pixels, 120 dpi vertical and horizontal resolution 
> (right click on a file, properties, summary, what does it mean?), the 
> second file is 4300x2222 pixels, 120 dpi vertical and horizontal 
> resolution. Seems ok. The second image is "doubled" in pixel size.
> 
> Now, when I try to print this image on A4 paper, using 300dpi, the images 
> are the same, there is no "better quality" in second image.
> 
> I have just finshed reading the Mapserver thread on "Change image 
> resolution in mapfile". Several limitations are mentioned there - max. 
> image size supported by Mapserver, "resolution" value/tag embedded in 
> output format, etc. Can it be related to my problem? Or is it maybe that 
> software I am using to print this image doesn't "use" this extra pixels? 
> Or I am just missing some basic stuff I need to know :-(
> 
> 
> thanks very much on any explanation
> 
> regards, dejan