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Lavorare con i dati raster

This section describes how to visualize and set raster layer properties. QGIS uses the GDAL library to read and write raster data formats, including ArcInfo Binary Grid, ArcInfo ASCII Grid, GeoTIFF, ERDAS IMAGINE, and many more. GRASS raster support is supplied by a native QGIS data provider plugin. The raster data can also be loaded in read mode from zip and gzip archives into QGIS.

Attualmente, la libreria GDAL supporta più di 100 formati raster (vedi GDAL-SOFTWARE-SUITE Letteratura e riferimenti web). La lista completa è disponibile alla pagina web http://www.gdal.org/formats_list.html.

Nota

Not all of the listed formats may work in QGIS for various reasons. For example, some require external commercial libraries, or the GDAL installation of your OS may not have been built to support the format you want to use. Only those formats that have been well tested will appear in the list of file types when loading a raster into QGIS. Other untested formats can be loaded by selecting the [GDAL] All files (*) filter.

Per caricare e lavorare con dati raster di GRASS, fai riferimento alla sezione Integrazione con GRASS GIS.

Cosa sono i dati raster?

Raster data in GIS are matrices of discrete cells that represent features on, above or below the earth’s surface. Each cell in the raster grid is the same size, and cells are usually rectangular (in QGIS they will always be rectangular). Typical raster datasets include remote sensing data, such as aerial photography, or satellite imagery and modelled data, such as an elevation matrix.

Unlike vector data, raster data typically do not have an associated database record for each cell. They are geocoded by pixel resolution and the x/y coordinate of a corner pixel of the raster layer. This allows QGIS to position the data correctly in the map canvas.

QGIS makes use of georeference information inside the raster layer (e.g., GeoTiff) or in an appropriate world file to properly display the data.

Loading raster data in QGIS

Raster layers are loaded either by clicking on the mActionAddRasterLayer Add Raster Layer icon or by selecting the Layer ‣ mActionAddRasterLayer Add Raster Layer menu option. More than one layer can be loaded at the same time by holding down the Ctrl or Shift key and clicking on multiple items in the Open a GDAL Supported Raster Data Source dialog.

Una volta caricato il raster puoi cliccare sul suo nome nella legenda con il tasto destro del mouse per selezionare ed attivare opzioni specifiche, o per aprire la finestra per l’impostazione delle proprietà.

Menu contestuale per layer raster

  • Zoom all’estensione del layer

  • Zoom alla scala migliore (100%)

  • Stira usando l’estensione attuale

  • Aggiungi alla panoramica

  • Rimuovi

  • Duplica

  • Set Layer CRS

  • Imposta il SR del progetto dal layer

  • Salva come ...

  • Proprietà

  • Rinomina

  • Copia lo stile

  • Add New Group

  • Espandi tutto

  • Comprimi tutto

  • Aggiorna l’ordine del disegno