grouping raster tiles for mapserv WMS

[Brent Fraser]

Jeff,

  Each level of the multi-level pyramid will be a separate layer with a
separate tileindex, and with the MINSCALE and MAXSCALE set so that only one
layer (level) will be rendered by MapServer when requested by the client
application.

So for example you might have:

    Level 1:     100 tiff files at 15m resolution with tileindex: level1.shp
                                    # MINSCALE
                                    MAXSCALE  250000   # 1:250k

    Level 2:       10 tiff files at 50m resolution with tileindex:
level2.shp
                                    MINSCALE    250000
                                    MAXSCALE  1000000  # 1:1m

    Level 3:         1 tiff file at 200m resolution (no tileindex required)
                                    MINSCALE 1000000    # 1:1m
                                    # MAXSCALE

The units are the right-hand side of a scale statement, but for a geographic
coordinate system (lat/lon) it's only very approximate so the values may
need some tweaking...

 FYI, my rule-of-thumb for relating resolution of imagery to mappping scale
is:
        <resolution in meters> X 4,000 = mapping scale

    LandSat:    14.25m X 4,000 =  57,000 (So after zooming in past 1:60,000,
you see pixelation)
    Modis:        250m   X 4,000  = 1,000,000  (1:1m at best)