GeoTIFF overviews / TILEINDEX / Large dataset performance

[Frank Warmerdam]

On 6/13/05, Gambin Dejan <Dejan.Gambin at pula.hr> wrote:
> 1. Frank talks about different types of tilings and overviews:
>         - is the tiling type related to overview type and how? To be
> more concrete, if I have a set of tiff files (and i am using tileindex
> shapefile to associate thme into one layer) can I use internal
> overviews? Which are the possible combinations? What are the advantages
> and disadvantages? Is it better to use internal overviews/tiles or what?

Gambin, 

My suggestion is to use internal overviews on your base files, but 
still to provide *some* additional overview map layers.  The built-in
overviews work fine for extracting overview images efficiently, but 
if the user zooms out a long ways such that they are looking at hundreds
of files, the very action of opening and parsing the headers of the many files  
will end up slowing things down alot. 

So the "map overview layers" are essentially intended to prevent MapServer
from having to touch too many files for any one render request. 

> 3. This is not so much related to overviews/tiles but I would like to
> know if there is any difference in using tiffs with their associating
> world files or real Geotiffs that have the geocoding informations
> embedded within the file? Is there any benefits to convert to "real"
> geotiff files using for example geotifcp utility?