[Mapserver-users] .tiff resolution

[Ed McNierney]

Charlton -

If you have the data in a shapefile, you will get MUCH better output results by serving that data as a shapefile in MapServer than by converting it to a TIF and then serving the TIF.  Both processes essentially do the same thing (generate a raster image) but MapServer can customize that image each time to the requested output resolution, whereas the TIF image is frozen at a particular resolution.

	- Ed

Ed McNierney
President and Chief Mapmaker
TopoZone.com / Maps a la carte, Inc.
73 Princeton Street, Suite 305
North Chelmsford, MA  01863
ed at topozone.com
(978) 251-4242 

-----Original Message-----
From: Charlton Purvis [mailto:cpurvis at asgnet.psc.sc.edu]
Sent: Friday, February 07, 2003 1:30 PM
To: Hankley, Chip; MapServer List (E-mail)
Subject: RE: [Mapserver-users] .tiff resolution


Thanks, Chip:

Explaining the layout of the .wld was very helpful.  Your computations
were correct.  But I'm still not completely satisfied w/ my final
product.  I'm w/i the 8 bit limit, and converting the tif to gif under
Photoshop keeps the image the same.  So I'm not convinced that it's a
display problem or a gif limitation.

But maybe I should backup and ask you (and the list) if my approach is
off-base.  I've been playing w/ the Canada demo as well, and I noticed
that the actual width and height of the Canada tif is large.  My
resulting tif (from my data) is not.

My goal (right now) is to go from a dem to tif.  Let's fast-forward and
work w/ the fact that I can get the dem to a shapefile.  From that
point, all I want to do is to export the shapefile to a tif (w/ the .wld
being created as well).  Am I going around my rear end to get to my
elbow?  I'm sure.  But am I missing something critical to preserving the
quality of the data when I go from the shapefile to the tif (ArcMap)?

Thanks again,

Charlton

-----Original Message-----
From: Hankley, Chip [mailto:Chip.Hankley at GASAI.Com] 
Sent: Friday, February 07, 2003 11:41 AM
To: Charlton Purvis; MapServer List (E-mail)
Subject: RE: [Mapserver-users] .tiff resolution

Charlton...

I'm getting different extents than you are. My calcs:

EXTENT 593226.92463 3623834.999945 605723.07543 3637755

Here's how I did it:

31.24	 - cell width
0.00	 - rotation
0.00	 - rotation
-31.28 - cell height	 
593226.92 - ULx (NOTE UL is Upper Left Corner)	
3637755.00 - ULy
400.00 - Image Width (pixels)
445.00 - Image Height (pixels)	
Top	      3637755.00  (ULy)
Bottom	3623835     (ULy + [cell height] * [image height])
Left	      593226.92   (ULx)
Right  	605723.0754 (ULx + [cell width] * [image width])


As far as image quality goes, make sure you're comparing apples to
apples.
Is the native image 8 bit (256 colors) or 24 bit? Also, if it's a TIFF,
you're output is likely either PNG, or GIF. This also will result in
some
differences.

Chip 

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