About ShapeTree and Raster TileIndex

[Akio Neuchi]

Frank,

I see what you mean. The volume and size do matter.
By the way, instead of Gif, how would be Tiff or GeoTiff?
People told me Tiffs are bigger and less efficient to render map images.
And what is good using GeoTiff instead of just Tiff?

Best regards,
Akio

-----Original Message-----
From: Frank Warmerdam [mailto:fwarmerdam at gmail.com]
Sent: Friday, May 13, 2005 10:17 PM
To: Akio Neuchi
Cc: MAPSERVER-USERS at lists.umn.edu
Subject: Re: [UMN_MAPSERVER-USERS] About ShapeTree and Raster TileIndex


On 5/13/05, Akio Neuchi <neuchi at tci-com.biz> wrote:
> Hello to all,
>
> I just made a *.qix file from *.shp file for Raster TileIndex images --
> around 800 gif images,
> and tested with and without shape tree. The result was there is no
> difference in processing speed.

Akio,

Well, first, scanning 800 polygon records isn't going to take
a significant amount of time anyways, so adding a spatial index
to the tile index isn't likely to gain you much.   If you rendering
requests are slow it is likely due to factors other than scanning
the tileindex itself.

I would add that if map views end up intersecting multiple gif
images (or if the gif images are large) performance will suck.
Gif images are effectively "stream compressed" so to pull
out an overview, or a small section of a gif you essentially end
up having to decompress all or most of the gif file.  This makes gif
a pretty poor format for "geospatial databases".

> In addition, I have around 100 of Vector TileIndex shape directories,
> and If ShapeTree really works, I am planning to build *.qix for each
Vector
> shapes.

Spatial indexes on your vector tiles will make a substantial diffference
if your tiles contain alot of features, but typical renders only require
a small number of the features from one or a few tiles.   If the tiles
are quite small and your map views fairly broad, such that typically
most or all of the features from a tile are rendered, then spatial
indices won't help much.

You really need to think about what are typical requests for your
use pattern, and what would be making them slow before you can
plan an effective optimization strategy.

Best regards,
--
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