Subgroup: Raster

Class: QgsRasterLayer

class qgis.core.QgsRasterLayer

Bases: qgis._core.QgsMapLayer

Constructor. Provider is not set.

QgsRasterLayer(uri: str, baseName: str = ‘’, providerKey: str = ‘’, options: QgsRasterLayer.LayerOptions = QgsRasterLayer.LayerOptions())
This is the constructor for the RasterLayer class.

The main tasks carried out by the constructor are:

-Load the rasters default style (.qml) file if it exists

-Populate the RasterStatsVector with initial values for each band.

-Calculate the layer extents

-Determine whether the layer is gray, paletted or multiband.

-Assign sensible defaults for the red, green, blue and gray bands.

This class provides qgis with the ability to render raster datasets onto the mapcanvas.

The qgsrasterlayer class makes use of gdal for data io, and thus supports any gdal supported format. The constructor attempts to infer what type of file (LayerType) is being opened - not in terms of the file format (tif, ascii grid etc.) but rather in terms of whether the image is a GRAYSCALE, PaletteD or Multiband,

Within the three allowable raster layer types, there are 8 permutations of how a layer can actually be rendered. These are defined in the DrawingStyle enum and consist of:

SingleBandGray -> a GRAYSCALE layer drawn as a range of gray colors (0-255) SingleBandPseudoColor -> a GRAYSCALE layer drawn using a pseudocolor algorithm PalettedSingleBandGray -> a PaletteD layer drawn in gray scale (using only one of the color components) PalettedSingleBandPseudoColor -> a PaletteD layer having only one of its color components rendered as pseudo color PalettedMultiBandColor -> a PaletteD image where the bands contains 24bit color info and 8 bits is pulled out per color MultiBandSingleBandGray -> a layer containing 2 or more bands, but using only one band to produce a grayscale image MultiBandSingleBandPseudoColor -> a layer containing 2 or more bands, but using only one band to produce a pseudocolor image MultiBandColor -> a layer containing 2 or more bands, mapped to the three RGBcolors. In the case of a multiband with only two bands, one band will have to be mapped to more than one color

Each of the above mentioned drawing styles is implemented in its own draw* function. Some of the drawing styles listed above require statistics about the layer such as the min / max / mean / stddev etc. statistics for a band can be gathered using the bandStatistics function. Note that statistics gathering is a slow process and every effort should be made to call this function as few times as possible. For this reason, qgsraster has a vector class member to store stats for each band. The constructor initializes this vector on startup, but only populates the band name and number fields.

Note that where bands are of gdal ‘undefined’ type, their values may exceed the renderable range of 0-255. Because of this a linear scaling histogram enhanceContrast is applied to undefined layers to normalise the data into the 0-255 range.

A qgsrasterlayer band can be referred to either by name or by number (base=1). It should be noted that band names as stored in datafiles may not be unique, and so the rasterlayer class appends the band number in brackets behind each band name.

Sample usage of the QgsRasterLayer class:

In order to automate redrawing of a raster layer, you should like it to a map canvas like this :

Once a layer has been created you can find out what type of layer it is (GrayOrUndefined, Palette or Multiband):

Raster layers can also have an arbitrary level of transparency defined, and have their color palettes inverted using the setTransparency and setInvertHistogram methods.

Pseudocolor images can have their output adjusted to a given number of standard deviations using the setStandardDeviations method.

The final area of functionality you may be interested in is band mapping. Band mapping allows you to choose arbitrary band -> color mappings and is applicable only to Palette and Multiband rasters, There are four mappings that can be made: red, green, blue and gray. Mappings are non-exclusive. That is a given band can be assigned to no, some or all color mappings. The constructor sets sensible defaults for band mappings but these can be overridden at run time using the setRedBandName, setGreenBandName, setBlueBandName and setGrayBandName methods.

Methods

appendError
bandCount Get the number of bands in this layer
bandName Get the name of a band given its number
brightnessFilter
childEvent
clone Returns a new instance equivalent to this one.
connectNotify
constDataProvider
createMapRenderer
customEvent
dataProvider
disconnectNotify
draw This is an overloaded version of the draw() function that is called by both draw() and thumbnailAsPixmap
hasDependencyCycle
height Accessor that returns the height of the (unclipped) raster
htmlMetadata
hueSaturationFilter
isSignalConnected
isSpatial
isValidRasterFileName This helper checks to see whether the file name appears to be a valid raster file name.
lastModified Return time stamp for given file name
legendSymbologyItems Returns a list with classification items (Text and color)
paletteAsPixmap Returns a 100x100 pixmap of the color palette.
pipe Get raster pipe
previewAsImage Draws a preview of the rasterlayer into a QImage
providerType [ data provider interface ] Which provider is being used for this Raster Layer?
rasterType Accessor for raster layer type (which is a read only property)
rasterUnitsPerPixelX Returns the number of raster units per each raster pixel in X axis.
rasterUnitsPerPixelY Returns the number of raster units per each raster pixel in Y axis.
readCommonStyle
readCustomProperties
readStyle
readStyleManager
readSymbology
readXml
receivers
reload
renderer
resampleFilter Set raster resample filter.
sender
senderSignalIndex
setContrastEnhancement Set contrast enhancement algorithm
setDataProvider [ data provider interface ] Set the data provider
setDefaultContrastEnhancement Set default contrast enhancement
setError
setExtent
setLayerOrder
setRenderer Set raster renderer.
setSubLayerVisibility
setValid
showStatusMessage
subLayers
timerEvent
timestamp
width Accessor that returns the width of the (unclipped) raster
writeCommonStyle
writeCustomProperties
writeStyle
writeStyleManager
writeSymbology
writeXml

Signals

Attributes

ColorLayer
ColorRampShader
FreakOutShader
GrayOrUndefined
MULTIPLE_BAND_MULTI_BYTE_ENHANCEMENT_ALGORITHM
MULTIPLE_BAND_MULTI_BYTE_MIN_MAX_LIMITS
MULTIPLE_BAND_SINGLE_BYTE_ENHANCEMENT_ALGORITHM
MULTIPLE_BAND_SINGLE_BYTE_MIN_MAX_LIMITS
Multiband
Palette
PseudoColorShader
SAMPLE_SIZE
SINGLE_BAND_ENHANCEMENT_ALGORITHM
SINGLE_BAND_MIN_MAX_LIMITS
UndefinedShader
UserDefinedShader
ColorLayer = 3
ColorRampShader = 3
class ColorShadingAlgorithm

Bases: int

FreakOutShader = 2
GrayOrUndefined = 0
class LayerOptions(loadDefaultStyle: bool = True)

Bases: sip.wrapper

Constructor for LayerOptions.

QgsRasterLayer.LayerOptions(QgsRasterLayer.LayerOptions)

loadDefaultStyle
class LayerType

Bases: int

MULTIPLE_BAND_MULTI_BYTE_ENHANCEMENT_ALGORITHM = 1
MULTIPLE_BAND_MULTI_BYTE_MIN_MAX_LIMITS = 3
MULTIPLE_BAND_SINGLE_BYTE_ENHANCEMENT_ALGORITHM = 0
MULTIPLE_BAND_SINGLE_BYTE_MIN_MAX_LIMITS = 1
Multiband = 2
Palette = 1
PseudoColorShader = 1
SAMPLE_SIZE = 250000.0
SINGLE_BAND_ENHANCEMENT_ALGORITHM = 1
SINGLE_BAND_MIN_MAX_LIMITS = 1
UndefinedShader = 0
UserDefinedShader = 4
appendError()
bandCount(self) → int

Get the number of bands in this layer

bandName(self, bandNoInt: int) → str

Get the name of a band given its number

brightnessFilter(self) → QgsBrightnessContrastFilter
childEvent()
clone(self) → QgsRasterLayer

Returns a new instance equivalent to this one. A new provider is created for the same data source and renderer is cloned too.

Returns:a new layer instance

New in version 3.0.

connectNotify()
constDataProvider(self) → QgsRasterDataProvider
createMapRenderer(self, rendererContext: QgsRenderContext) → QgsMapLayerRenderer
customEvent()
dataProvider(self) → QgsRasterDataProvider
disconnectNotify()
draw(self, theQPainter: QPainter, myRasterViewPort: QgsRasterViewPort, qgsMapToPixel: QgsMapToPixel = None)

This is an overloaded version of the draw() function that is called by both draw() and thumbnailAsPixmap

hasDependencyCycle()
height(self) → int

Accessor that returns the height of the (unclipped) raster

htmlMetadata(self) → str
hueSaturationFilter(self) → QgsHueSaturationFilter
isSignalConnected()
isSpatial(self) → bool
isValidRasterFileName(fileNameQString: str, retError: str) → bool

This helper checks to see whether the file name appears to be a valid raster file name. If the file name looks like it could be valid, but some sort of error occurs in processing the file, the error is returned in retError.

isValidRasterFileName(fileNameQString: str) -> bool

lastModified(name: str) → QDateTime

Return time stamp for given file name

legendSymbologyItems(self) → object

Returns a list with classification items (Text and color)

paletteAsPixmap(self, bandNumber: int = 1) → QPixmap

Returns a 100x100 pixmap of the color palette. If the layer has no palette a white pixmap will be returned

Parameters:bandNumber – the number of the band to use for generating a pixmap of the associated palette
pipe(self) → QgsRasterPipe

Get raster pipe

previewAsImage(self, size: QSize, bgColor: Union[QColor, Qt.GlobalColor] = Qt.white, format: QImage.Format = QImage.Format_ARGB32_Premultiplied) → QImage

Draws a preview of the rasterlayer into a QImage

New in version 2.4.

providerType(self) → str

[ data provider interface ] Which provider is being used for this Raster Layer?

rasterType(self) → QgsRasterLayer.LayerType

Accessor for raster layer type (which is a read only property)

rasterUnitsPerPixelX(self) → float

Returns the number of raster units per each raster pixel in X axis.

In a world file, this is normally the first row (without the sign). (E.g. the value reported by the GDAL geotransform[1]).

rasterUnitsPerPixelY(self) → float

Returns the number of raster units per each raster pixel in Y axis.

In a world file, this is normally the first row (without the sign).

readCommonStyle()
readCustomProperties()
readStyle(self, node: QDomNode, errorMessage: str, context: QgsReadWriteContext) → bool
readStyleManager()
readSymbology(self, node: QDomNode, errorMessage: str, context: QgsReadWriteContext) → bool
readXml(self, layer_node: QDomNode, context: QgsReadWriteContext) → bool
receivers()
reload(self)
renderer(self) → QgsRasterRenderer
resampleFilter(self) → QgsRasterResampleFilter

Set raster resample filter. Takes ownership of the resample filter object

sender()
senderSignalIndex()
setContrastEnhancement(self, algorithm: QgsContrastEnhancement.ContrastEnhancementAlgorithm, limits: QgsRasterMinMaxOrigin.Limits = QgsRasterMinMaxOrigin.MinMax, extent: QgsRectangle = QgsRectangle(), sampleSize: int = QgsRasterLayer.SAMPLE_SIZE, generateLookupTableFlag: bool = True)

Set contrast enhancement algorithm

Parameters:
  • algorithm – Contrast enhancement algorithm
  • limits – Limits
  • extent – Extent used to calculate limits, if empty, use full layer extent
  • sampleSize – Size of data sample to calculate limits, if 0, use full resolution
  • generateLookupTableFlag – Generate lookup table. *
setDataProvider(self, provider: str)

[ data provider interface ] Set the data provider

setDefaultContrastEnhancement(self)

Set default contrast enhancement

setError()
setExtent()
setLayerOrder(self, layers: Iterable[str])
setRenderer(self, renderer: QgsRasterRenderer)

Set raster renderer. Takes ownership of the renderer object

setSubLayerVisibility(self, name: str, vis: bool)
setValid()
showStatusMessage(self, message: str)
subLayers(self) → List[str]
timerEvent()
timestamp(self) → QDateTime
width(self) → int

Accessor that returns the width of the (unclipped) raster

writeCommonStyle()
writeCustomProperties()
writeStyle(self, node: QDomNode, doc: QDomDocument, errorMessage: str, context: QgsReadWriteContext) → bool
writeStyleManager()
writeSymbology(self, a0: QDomNode, doc: QDomDocument, errorMessage: str, context: QgsReadWriteContext) → bool
writeXml(self, layer_node: QDomNode, doc: QDomDocument, context: QgsReadWriteContext) → bool