[Mapserver-dev] Generic tiling (for shapefiles and rasters)...

[woodbri at swoodbridge.com]

Hi Steve,

We talked about the need to improve on the tile4ms to validate the 
all the files being added to the tileindex have the same fields and 
order of fields. What about creating a tileindex.mdt file that would 
be a metadata file with the template info for the tileindex. This 
file can be created by tile4ms and be a simple text file that anyone 
anyone can create that has the dbf definition that was validated when 
tile4 ms was run.

This file could be opened if the tileindex is a shapfile instead of 
scanning the files. This would imply that for non shapfile 
tileindexes that you can request a similar metadata structure for the 
layer.

Another option would be to require the meta data to included in the 
METADATA ...END object of the LAYER in the mapfile is the data layer 
is shapfiles.

How does this play with the fact that I build tileindexes for Tiger 
data based on the county directory and not on the actual files in the 
layer. So the data is organized like this:

SHAPEPATH "/data/mdata/"

LAYER
  TILEINDEX "tiger-tile"
  DATA "roads"
END
LAYER
  TILEINDEX "tiger-tile"
  DATA "waterpoly"
END

the LOCATION in the tileindex look like
/data/mdata/tiger2k/25/25015/
/data/mdata/tiger2k/25/25017/
etc

and 

files are like:

/data/mdata/tiger2k/25/25015/roads.*
/data/mdata/tiger2k/25/25015/waterpoly.*
/data/mdata/tiger2k/25/25017roads.*
/data/mdata/tiger2k/25/25017/waterpoly.*
etc

This cuts down on the number of records in the tileindex from about 
33,000 to about 3300 at the minor expense that some layers are 
marginally smaller than the county bounds, but the biggest layers 
"roads" always defines the boundary anyway. and drives performance.

-Steve W.


On 8 Mar 2004 at 17:06, Steve Lime wrote:

> Hi Folks: As I've been putzing with enhanced tiling support I've been
> trying to generalize things
> so that one wouldn't be limited to simply shapefile tile indexes. For
> raster data that shouldn't be
> an issue using another LAYER as a tile layer. This would allow you, for
> example, to store your
> tileindex in PostGIS and reference images on the file system. For
> shapefiles it's not that simple
> though because of this need to open one tile as a template (to get item
> names and such). I can'd
> find an easy way to retrieve, for example, the 1st record in a layer.
> (For rasters this isn't an 
> issue since we don't need a template.)
> 
> So, there are a couple of options:
> 
>   - say the hell with non-shapefile tile indexes for shapefiles, but
> allow them for rasters
> 
>   - figure out a method to retrieve the nth element of a datasource
> (not by ID, but by position)
> 
>   - retool the msLayer... functions and move the msLayerWhichItems
> functionality someplace else
> 
> I'm partial to the first one. I can't imagine anyone using
> non-shapefile tile indexes with shapefiles 
> (I mean, most folks would put everything in PostGIS or SDE). Raster
> data are where that functionality
> makes sense.
> 
> I just want to run the idea by folks to make sure I'm not overlooking
> some obvious solution.
> 
> Steve
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