A demo of Generating Google Tiles With mapserver

[Jon Saints]

I will be sharing everything.


--- Patrick Weber <p.weber at UCL.AC.UK> wrote:

> Great it works perfect with my PC , running firefox.
> Amazing and its
> quite fast. The Washington DC example could use some
> labels I want to
> find the White House !!!
>
> Hope you can share your implementation with the
> mailing list soon, this
> has great potential !
>
>
> Jon Saints wrote:
> > I have implemented a demo using python mapscript
> and
> > mapserver that gives very basic functionality
> simillar
> > to google maps.
> >
> > I do not pre-render maps at the various scales.
> > mapscale are rendered on the fly and the indiviual
> > tile images are sent directly to the user - never
> > saved on disk.  I know this will cause problems
> for
> > labeling, but there may be a way around this with
> some
> > DHTML tricks.
> >
> > Please remember that this demo is running off of
> my
> > desktop computer over a wifi connection.
> performance
> > may be very slow and my poor desktop might crash
> with
> > too many hits. I offer only a proof of concept and
> > welcome coments from the list.
> >
> > Right now the demo only works in Mozilla Firefox
> (on
> > Win, Linux and OsX).  If you zoom in far enough on
> the
> > washington DC map you will see aerial photos.
> >
> >
> > Click the "START HERE" button to start the app.
> >
> http://216.15.56.185:8080/jons/indon/client/test.xul
> >
> > Thanks
> > JOn
> >
> >
> >
> >
> >
> >
> >
> > --- Stephen Woodbridge <woodbri at SWOODBRIDGE.COM>
> > wrote:
> >
> >>Hi all,
> >>
> >>I posted about generating google-like tiles using
> >>mapserver earlier. I
> >>took it to the next step of writing a
> perl/mapscript
> >>script to compute
> >>the cellsize for each zoom scale and used that to
> >>compute the number of
> >>tiles I would need to generate to cover my map
> >>extents. I thought I
> >>would share the results with you. You can probably
> >>save maybe 20-30% on
> >>the number of tiles if you can recognize all water
> >>only tiles and
> >>eliminate them, but this leaves you with 70-80% of
> >>what looks like
> >>infinity for most of us.
> >>
> >>        Scale   Num Tiles
> >>   ---------- -----------
> >>     50000000         256
> >>      4000000        3072
> >>      1000000       40960
> >>       500000      150784
> >>       150000     1634816
> >>        50000    14586880
> >>        15000   161796096
> >>        10000   363410944
> >>         5000  1453643776
> >>         2700  4984920576
> >>   ---------- -----------
> >>  Total Tiles  6980188160
> >>  Approx. Disk Space (assume 3K per tile) =
> >>21,443,138,027,520
> >>
> >>SOoooo, it requires about 7 Billion 128x128 tiles
> >>and assuming that the
> >>average tile size is about 3K (the smallest tile
> >>that I have seen google
> >>return) it requires 21 Tera bytes of disk space.
> It
> >>gets worse!
> >>
> >>If you assume you can generate 1000 tiles minute
> >>(16+/sec) then:
> >>
> >>6,980,188,160 / 1000 tiles/min / 60 min/hr / 24
> >>hr/day / 365 day/yr =
> >>13.3 yrs
> >>
> >>   1,000 tiles/min = 13.3 yr =  4847 days
> >>  10,000 tiles/min = 1.33 yr =   485 days
> >>100,000 tiles/min = 0.13 yr =    49 days
> >>
> >>The only way to do the higher generation rates is
> in
> >>a highly
> >>distributed environment or you run into I/O bottle
> >>necks both reading
> >>and writing data.
> >>
> >>Oh yeah, I only used 10 zoom scales above, Google
> >>has 15, so you do the
> >>math :)
> >>
> >>An alternative to pre generating the tiles, is
> >>generating them on the
> >>fly as they are need and caching them, then
> removing
> >>the least used ones
> >>over time. This is a much more complicated
> scenario
> >>and requires a lot
> >>of additional code to manage them. Also you can
> not
> >>just generate a
> >>single tile as needed because of the way mapserver
> >>handles dynamic
> >>placement of labels. You would need to generate a
> >>"super" tile of say
> >>8x8 or 16x16 tiles and chop it into the standard
> >>tiles. I looked at
> >>generating a 16x16 super tile at 2048x2048 pixels
> >>that would get chopped
> >>into 256 tiles for pre-generation, but 6x6 tiles
> >>(768x768 pixels) might
> >>be better for dynamic generation. You would have
> to
> >>find the sweet spot
> >>where the super tile is large enough to minimize
> >>labeling issues and
> >>small enough the it generates and chops quickly.
> >>
> >>-Steve W.
> >>
>
> --
> ________________________________________
>
>    Patrick Weber | p.weber at ucl.ac.uk
>
>    Research Associate
>
>    Centre for Advanced Spatial Analysis
>    http://www.casa.ucl.ac.uk/
>
>    University College London
> ________________________________________
>