Overview Images in Mapserver

[Ed McNierney]

Kenneth -

Provided MapServer is built using GDAL (which it will be, if you're
seeing 24-bit GeoTIFFs at all) then the overviews will be used
automatically.

For the best possible performance you will have overviews that precisely
match the scale of the requested image.  GDAL will use the overview with
the lowest resolution that is not less than the requested resolution,
and resample from there.  If you create a 3x overview and then zoom out
by a factor of 2, that overview won't be used at all.

	- 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: UMN MapServer Users List [mailto:MAPSERVER-USERS at LISTS.UMN.EDU] On
Behalf Of Kenneth Denson
Sent: Friday, July 08, 2005 12:50 PM
To: MAPSERVER-USERS at LISTS.UMN.EDU
Subject: [UMN_MAPSERVER-USERS] Overview Images in Mapserver

I have 9 24-bit geotiffs that I've indexed using gdaltindex. They
display just perfectly in mapserver, but the problem is that it can be a
little slow. I've used gdaladdo to add some overview levels to the
geotiffs, but how do I tell mapserver to use those overviews? Or is it
doing it automatically? Just for reference, the following is the
information about the geotiffs and how their layer looks in mapserver.

Size is 10000, 10000
Coordinate System is `'
Origin = (2360000.000000,850000.000000)
Pixel Size = (0.500000,-0.500000)
Metadata:
  TIFFTAG_SOFTWARE=Adobe Photoshop 7.0
  TIFFTAG_DATETIME=2003:11:17 17:34:02
Corner Coordinates:
Upper Left  ( 2360000.000,  850000.000)
Lower Left  ( 2360000.000,  845000.000)
Upper Right ( 2365000.000,  850000.000)
Lower Right ( 2365000.000,  845000.000)
Center      ( 2362500.000,  847500.000)
Band 1 Block=10000x1 Type=Byte, ColorInterp=Red
  Overviews: 3x3, 3x3, 3x3, 3x3, 3x3, 3x3, 3x3, 3x3, 5000x5000,
2500x2500, 1667x1667, 1250x1250, 1000x1000 Band 2 Block=10000x1
Type=Byte, ColorInterp=Green
  Overviews: 3x3, 3x3, 3x3, 3x3, 3x3, 3x3, 3x3, 3x3, 5000x5000,
2500x2500, 1667x1667, 1250x1250, 1000x1000 Band 3 Block=10000x1
Type=Byte, ColorInterp=Blue
  Overviews: 3x3, 3x3, 3x3, 3x3, 3x3, 3x3, 3x3, 3x3, 5000x5000,
2500x2500, 1667x1667, 1250x1250, 1000x1000


LAYER
    NAME "orthophoto"
    METADATA
      "tiles" "orthophoto"
    END
    STATUS ON
    TILEINDEX "tiles.shp"
    TILEITEM "location"
    TYPE RASTER
END

Kenneth Denson
Spatial Focus Inc.
kdenson at spatialfocus.com