Changes between Version 12 and Version 13 of WKTRaster/SeamlessArchitecture

Timestamp:

Jul 19, 2011, 7:20:36 AM (13 years ago)

Author:

bnordgren

Comment:

—

WKTRaster/SeamlessArchitecture

@@ -45 +45 @@
 Within the context of a relational database, there are two ways to represent a `CV_GeometryValuePair`. A special type may be created which has two fields: one a geometry and the other a numeric value. In PostGIS Raster, this type is called `geomval`. More generally, any table (or query) with one or more geometry columns may represent a collection of `CV_GeometryValuePair`s. Each row of such a table is a single association. In this latter case, it is necessary to pick one of the geometry columns to act as the `geometry` field. All other columns are part of the `value` field. 
 
-  '''Example:''' A table with a geometry field called `geom` and three numeric fields called `band1`, `band2`, and `band3` could represent a collection of `CV_GeometryValuePair`s. Each row associates a single geometry with three numbers. If the data are to be displayed on a map, the geometry column contains the shapes which are drawn, and the value columns (everything else) may be used to select geometries to display, or may affect the display in some way (e.g., set the rotation, size or color of the symbol.) 
+  '''Example:''' A table with a geometry column called `geom` and three numeric columns called `band1`, `band2`, and `band3` could represent a collection of `CV_GeometryValuePair`s. Each row associates a single geometry with three numbers. If the data are to be displayed on a map, the geometry column contains the shapes which are drawn, and the value columns (everything else) may be used to select geometries to display, or may affect the display in some way (e.g., set the rotation, size or color of the symbol.) 
 
 Note that it is possible to have non-numeric values in this generic case where `CV_GeometryValuePair` is represented by a table. One of the value columns may be `text`, or `timestamp`. This is allowed by ISO 19123, and is a fairly commonplace occurrence when making a vector coverage (e.g., a "label" field in a value attribute table). The above limitation, where values are restricted to numeric types, applies when the set of `CV_GeometryValuePair`s is backed by an image format. Image formats do not store dates or strings for every pixel. Therefore, rasters have a limitation on allowable data types of the value fields which vectors do not.