What is a "Nodata value"
From AWF-Wiki
(Difference between revisions)
m (Nnoelke moved page Nodata value to What is a "Nodata value" without leaving a redirect) |
|||
(One intermediate revision by one user not shown) | |||
Line 1: | Line 1: | ||
− | |||
− | |||
A nodata value simply is a pixel value in a vector or raster map representing no information. It is ''not to be confused'' with a pixel value of ''0'' (zero). | A nodata value simply is a pixel value in a vector or raster map representing no information. It is ''not to be confused'' with a pixel value of ''0'' (zero). | ||
Line 34: | Line 32: | ||
In [[QGIS]], information on the nodata value can be obtained from the layer properties ({{button|text=Metadata)}} and/or {{button|text=General}} tab). | In [[QGIS]], information on the nodata value can be obtained from the layer properties ({{button|text=Metadata)}} and/or {{button|text=General}} tab). | ||
− | [[category: | + | [[category: FAQ (QGIS Tutorial)]] |
Latest revision as of 16:36, 16 September 2014
A nodata value simply is a pixel value in a vector or raster map representing no information. It is not to be confused with a pixel value of 0 (zero).
E.g. in a raster-map containing temperatures of a surface in °C, a pixel value of 0 represents a temperature of 0 °C, while a nodata-pixel simply represents a part of the surface where no information on the temperature is available.
Accumulations of neighboring pixels result in so called “nodata-areas”.
The way nodata values are saved depends on the respective data type, but may also vary within. They may be saved as numbers or strings. Examples are shown in the table below.
Data type | Nodata value (string) | Nodata value (number) |
---|---|---|
GRASS raster | null | |
GeoTIFF | nan | |
Arc/Info ASCII Grid | -9999 |
In QGIS, information on the nodata value can be obtained from the layer properties (Metadata) and/or General tab).