From c81bd48f6c1912e62bda084f35300462db7420a9 Mon Sep 17 00:00:00 2001 From: Regina Obe Date: Thu, 15 Dec 2011 01:56:39 +0000 Subject: [PATCH] more reasons why we have raster overviews git-svn-id: http://svn.osgeo.org/postgis/trunk@8425 b70326c6-7e19-0410-871a-916f4a2858ee --- doc/using_raster_dataman.xml | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/doc/using_raster_dataman.xml b/doc/using_raster_dataman.xml index 7c51ee415..1c0b4100e 100644 --- a/doc/using_raster_dataman.xml +++ b/doc/using_raster_dataman.xml @@ -291,11 +291,11 @@ psql -d gisdb -f elev.sql Raster Overviews - raster_overviews catalogs information about raster table columns used for overviews and additional information about them that is useful to know when utilizing overviews. Overview tables are cataloged in both raster_columns and raster_overviews because they are rasters in their own right but also serve an additional special purpose. These are generated along-side the main raster table when you use the -l switch in raster loading. + raster_overviews catalogs information about raster table columns used for overviews and additional information about them that is useful to know when utilizing overviews. Overview tables are cataloged in both raster_columns and raster_overviews because they are rasters in their own right but also serve an additional special purpose of being a lower resolution caricature of a higher resolution table. These are generated along-side the main raster table when you use the -l switch in raster loading. Two main reasons for overviews are: - Low resolution representation of the core tables common used for fast mapping zoom-out. - Computations are faster to do on them though the computations are not as accurate as the high-res tables, they can be suitable in many rule-of-thumb computations. + Low resolution representation of the core tables commonly used for fast mapping zoom-out. + Computations are generally faster to do on them than their higher resolution parents because there are fewer records and each pixel covers more territory. Though the computations are not as accurate as the high-res tables they support, they can be suitable in many rule-of-thumb computations. -- 2.40.0