What is a "Nodata value"
From AWF-Wiki
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Accumulations of neighboring pixels result in so called “nodata-areas”. | Accumulations of neighboring pixels result in so called “nodata-areas”. | ||
| + | |||
| + | The way nodata values are saved depends on the respective data type. They may be saved as numbers or [[string|strings]]. | ||
| + | Examples are shown in the table below. | ||
| + | |||
| + | {| class="wikitable" | ||
| + | |- | ||
| + | ! Data type | ||
| + | ! Nodata value (string) | ||
| + | ! Nodata value (number) | ||
| + | |- | ||
| + | | GRASS raster | ||
| + | | null | ||
| + | | | ||
| + | |- | ||
| + | |Arc/Info ASCII Grid | ||
| + | | | ||
| + | | -9999 | ||
| + | |- | ||
| + | |} | ||
[[category: Terms and definitions]] | [[category: Terms and definitions]] | ||
Revision as of 12:31, 18 February 2011
QGIS Tutorial
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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. 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 | |
| Arc/Info ASCII Grid | -9999 |
