[mapserver-users] Output image resolution - explanation needed

[Dejan.Gambin at pula.hr]

Thanks Steve

I still (unfortunatelly) don't understand why I am getting the "same 
quality" image on the paper with the first and second print (the second 
image has twice more pixels). Is it because of the input image itself? To 
be specific - the raster input is aerial image that gdalinfor reports as:

Driver: GTiff/GeoTIFF
Files: 5C14-05-DOF.tif
Size is 4500, 6000
Coordinate System is `'
Origin = (5419000.154658853100000,4964998.794652804700000)
Pixel Size = (0.499829146050620,-0.499829146050620)
Corner Coordinates:
Upper Left  ( 5419000.155, 4964998.795)
Lower Left  ( 5419000.155, 4961999.820)
Upper Right ( 5421249.386, 4964998.795)
Lower Right ( 5421249.386, 4961999.820)
Center      ( 5420124.770, 4963499.307)
Band 1 Block=256x256 Type=Byte, ColorInterp=Red
  Overviews: 2250x3000, 1125x1500, 563x750, 282x375
Band 2 Block=256x256 Type=Byte, ColorInterp=Green
  Overviews: 2250x3000, 1125x1500, 563x750, 282x375
Band 3 Block=256x256 Type=Byte, ColorInterp=Blue
  Overviews: 2250x3000, 1125x1500, 563x750, 282x375

regards, dejan

"Steve Lime" <Steve.Lime at dnr.state.mn.us> wrote on 30.07.2008 21:13:55:

> 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
> 
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