[mapserver-users] mapserver debug raster overview size

[Andy Colson]

I have some large aerial imagery (15 gig of mrsid).  I tried to convert 
it to geotiff with compress=lzw, but it comes out to 67 gig, without 
overviews.  So I won't be using that.

To test different options, I choose a 2.4 file and tried with 
compress=jpeg (and photometric=ycbcr) and the resulting file is 4.6 gig, 
with external overview file about 3 gig.  I only choose levels 2 4 8 and 
16, because that's whats in the example I found.

So my question is, how do I know what levels I should choose?

I turned on mapfile debugging and CPL_DEBUG hoping it would say 
something simple like "overview not found!".

perhaps it does tell me something though, but I'm not sure what.  Does 
any of this info tell me what overview it choose:

msDrawRasterLayerLow(arial2): entering.
GDAL: GDALOpen(/pub/maps/PhelpsMO/a2/phelpsmo_B2.tif, this=0x1a12060) 
succeeds as GTiff.
msResampleGDALToMap in effect: cellsize = 0.390799
msDrawGDAL(arial2): using RAW_WINDOW=86196 23174 10678 6869, 
dst=0,0,3549,2283
msDrawRasterLayerGDAL(): red,green,blue,alpha bands = 1,2,3,0
GDAL: GDALDefaultOverviews::OverviewScan()
GDAL: GDALOpen(/pub/maps/PhelpsMO/a2/phelpsmo_B2.tif.ovr, 
this=0x1a2ea60) succeeds as GTiff.
GTiff: ScanDirectories()
GTiff: Opened 37308x51730 overview.
GTiff: Opened 18654x25865 overview.
GTiff: Opened 9327x12933 overview.
GDAL: GDALClose(/pub/maps/PhelpsMO/a2/phelpsmo_B2.tif, this=0x1a12060)
GDAL: GDALClose(, this=0x1a2f430)
GDAL: GDALClose(, this=0x1a2f8a0)
GDAL: GDALClose(, this=0x1a316c0)
GDAL: GDALClose(/pub/maps/PhelpsMO/a2/phelpsmo_B2.tif.ovr, this=0x1a2ea60)
msDrawMap(): Layer 2 (arial2), 2.801s


I think the  RAW_WINDOW=86196 23174 10678 6869, dst=0,0,3549,2283 might 
have some useful info.. but I don't know what it means.

And I see it scanned through the overview's, but did it use any of them? 
  Which did it choose?

Any hints?

Thanks for your time,

-Andy