Help with TIFFTAGs resolutions

[Gambin Dejan]

I have just one question and that will be all: regarding the screen
resolution - which are the parameters that impact the screen resolution
of my map? If I shiw those images in DWG viewer they are very "sharp"
and look much better than shown on the map, with nearly the same display
dimensions....

Is there a way of modifying it?

regards, dejan

> -----Original Message-----
> From: Frank Warmerdam [mailto:warmerdam at pobox.com] 
> Sent: Thursday, July 12, 2007 8:58 PM
> To: Gambin Dejan
> Cc: MAPSERVER-USERS at LISTS.UMN.EDU
> Subject: Re: [UMN_MAPSERVER-USERS] Help with TIFFTAGs resolutions
> 
> Gambin Dejan wrote:
> > Hi,
> > 
> > I have a situation that I need to understand, I hope 
> someone can help:
> > 
> > I have a number of ortophoto images in tif format (with .tfw files).
> > When I show them on my map they should be spatialy 
> "connected" but the 
> > "empty" space shows between them. Here is the example 
> gdalinfo result 
> > of the two horizontally adjacent images that should be "connected":
> ...
> > Now, I have the similar set of ortophoto images that show correctly 
> > and they come from the same source (the National State Geodetic 
> > Administration). I have compared them and the difference is 
> that this 
> > "correct" images have the size of 4500x6000 (exactly 1.6 
> bigger than 
> > the first one) and their TIFFTAG_XRESOLUTION and 
> TIFFTAG_YRESOLUTION 
> > are 72 (that is 45x1.6).
> > 
> > My question is: who "made the mistake" and what do I have to do to 
> > show them correctly (they are shown correctly from a dwg 
> file that is 
> > referencing them all)? Are the TFW files wrong for this 
> resolution? Do 
> > I have to change the resolution, image size, or what?
> 
> Dejan,
> 
> It is unlikely that the DWG is utilizing the world files 
> (.tfw) at all.
> So if the DWG view is correct it is likely that the world 
> files are wrong.  If you think the origin's in the world 
> files are correct you could try changing the resolution in 
> the world files to 0.8 from 0.5 and see if things are properly placed.
> 
> The TIFFTAG_XRESOLUTION and TIFFTAG_YRESOLUTION are not used 
> for georeferenced placement or scaling by MapServer or other 
> applications.
> 
> BTW, GDAL and MapServer will utilize internal GeoTIFF tags in 
> preference to the world files.  So if there is wrong internal 
> geotiff info it will get used instead of potentially correct 
> worldfiles.  Keep this in mind if the world files don't seem 
> to agree with what gdalinfo is reporting.
> 
> Best regards,
> -- 
> ---------------------------------------+----------------------
> ----------
> ---------------------------------------+------
> I set the clouds in motion - turn up   | Frank Warmerdam, 
> warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush    | President OSGeo, 
> http://osgeo.org
> 
>