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Diálogo de propriedades do Raster

To view and set the properties for a raster layer, double click on the layer name in the map legend, or right click on the layer name and choose Properties from the context menu. This will open the Raster Layer Properties dialog (see figure_raster_properties).

There are several tabs in the dialog:

  • Geral

  • Estilo

  • Transparência

  • Pirâmides

  • Histograma

  • Metadados

  • Legend
../../../_images/rasterPropertiesDialog.png

Raster Layers Properties Dialog

Dica

Live update rendering

The Layer Styling Panel provides you with some of the common features of the Layer properties dialog and is a good modeless widget that you can use to speed up the configuration of the layer styles and automatically view your changes in the map canvas.

Nota

Because properties (symbology, label, actions, default values, forms...) of embedded layers (see Projetos animados) are pulled from the original project file and to avoid changes that may break this behavior, the layer properties dialog is made unavailable for these layers.

General Properties

Informação da camada

The General tab displays basic information about the selected raster, including the layer source path, the display name in the legend (which can be modified), and the number of columns, rows and no-data values of the raster.

Coordinate Reference System

Displays the layer’s Coordinate Reference System (CRS) as a PROJ.4 string. You can change the layer’s CRS, selecting a recently used one in the drop-down list or clicking on setProjection Select CRS button (see Coordinate Reference System Selector). Use this process only if the CRS applied to the layer is a wrong one or if none was applied. If you wish to reproject your data into another CRS, rather use layer reprojection algorithms from Processing or Save it into another layer.

Scale dependent visibility

You can set the Maximum (inclusive) and Minimum (exclusive) scale, defining a range of scale in which the layer will be visible. Out of this range, it’s hidden. The mapIdentification Set to current canvas scale button helps you use the current map canvas scale as boundary of the range visibility. See Escala dependente da renderização for more information.

Style Properties

Representar a banda

QGIS offers four different Render types. The renderer chosen is dependent on the data type.

  1. Color multibanda - se o arquivo vem como multibanda, com várias bandas (por exemplo, usado para imagens de satélite com várias bandas)

  2. Mapa de Cores - se um arquivo de banda única vem com um mapa de cores indexado (por exemplo, usado para mapas topográficos digitais)

  3. Singleband gray - (one band of) the image will be rendered as gray; QGIS will choose this renderer if the file has neither multibands nor an indexed palette nor a continuous palette (e.g., used with a shaded relief map)
  4. Banda única Falsa Cor - este método de representação é usado em arquivos com mapa de cores contínuos ou com mapa de cores (por exemplo, para mapa de elevações)

Multibanda Colorida

Para representar em color multibanda, selecione três bandas da imagem que vai representar, cada banda representa respectivamente, a componente vermelha, verde e azul, que serão usadas para criar a cor da imagem. Podem-se escolher vários métodos para Melhora do contraste : ‘Sem melhora’, ‘Estique para MinMax’, ‘Estique e corte no MinMax’ e ‘Corte no min max’.

../../../_images/rasterMultibandColor.png

Raster Style - Multiband color rendering

This selection offers you a wide range of options to modify the appearance of your raster layer. First of all, you have to get the data range from your image. This can be done by choosing the Extent and pressing [Load]. QGIS can radioButtonOn Estimate (faster) the Min and Max values of the bands or use the radioButtonOff Actual (slower) Accuracy.

Now you can scale the colors with the help of the Load min/max values section. A lot of images have a few very low and high data. These outliers can be eliminated using the radioButtonOn Cumulative count cut setting. The standard data range is set from 2% to 98% of the data values and can be adapted manually. With this setting, the gray character of the image can disappear. With the scaling option radioButtonOff Min/max, QGIS creates a color table with all of the data included in the original image (e.g., QGIS creates a color table with 256 values, given the fact that you have 8 bit bands). You can also calculate your color table using the radioButtonOff Mean +/- standard deviation x selectNumber. Then, only the values within the standard deviation or within multiple standard deviations are considered for the color table. This is useful when you have one or two cells with abnormally high values in a raster grid that are having a negative impact on the rendering of the raster.

All calculations can also be made for the radioButtonOff Current extent.

Dica

Visualizando uma única banda do Raster Multibanda

Se deseja ver uma única banda de uma imagem multibanda (por exemplo apenas a Vermelha), pode-se colocar as bandas Verde e Azul como “Não definidas”, mas isto não é a forma correta. Para mostrar apenas a banda Vermelha, coloque o tipo da imagem como ‘Banda única Cinza’, depois selecione o Vermelho como a banda para usar no Cinza.

Mapa de Cores

This is the standard render option for singleband files that already include a color table, where each pixel value is assigned to a certain color. In that case, the palette is rendered automatically. If you want to change colors assigned to certain values, just double-click on the color and the Select color dialog appears. Also, in QGIS it’s possible to assign a label to the color values. The label appears in the legend of the raster layer then.

../../../_images/rasterPaletted.png

Raster Style - Paletted Rendering

Melhora do contraste

Nota

When adding GRASS rasters, the option Contrast enhancement will always be set automatically to stretch to min max, regardless of if this is set to another value in the QGIS general options.

Banda única cinza

This renderer allows you to render a single band layer with a Color gradient: ‘Black to white’ or ‘White to black’. You can define a Min and a Max value by choosing the Extent first and then pressing [Load]. QGIS can radioButtonOn Estimate (faster) the Min and Max values of the bands or use the radioButtonOff Actual (slower) Accuracy.

../../../_images/rasterSingleBandGray.png

Raster Style - Singleband gray rendering

With the Load min/max values section, scaling of the color table is possible. Outliers can be eliminated using the radioButtonOn Cumulative count cut setting. The standard data range is set from 2% to 98% of the data values and can be adapted manually. With this setting, the gray character of the image can disappear. Further settings can be made with radioButtonOff Min/max and radioButtonOff Mean +/- standard deviation x selectNumber. While the first one creates a color table with all of the data included in the original image, the second creates a color table that only considers values within the standard deviation or within multiple standard deviations. This is useful when you have one or two cells with abnormally high values in a raster grid that are having a negative impact on the rendering of the raster.

Singleband pseudocolor

This is a render option for single-band files, including a continuous palette. You can also create individual color maps for the single bands here.

../../../_images/rasterSingleBandPseudocolor.png

Raster Style - Singleband pseudocolor rendering

Existem três tipos de interpolação de cores:

  1. Método Discreto

  2. Método Linear

  3. Método Exato

In the left block, the button signPlus Add values manually adds a value to the individual color table. The button signMinus Remove selected row deletes a value from the individual color table, and the arrowDown Sort colormap items button sorts the color table according to the pixel values in the value column. Double clicking on the value column lets you insert a specific value. Double clicking on the color column opens the dialog Change color, where you can select a color to apply on that value. Further, you can also add labels for each color, but this value won’t be displayed when you use the identify feature tool. You can also click on the button draw Load color map from band, which tries to load the table from the band (if it has any). And you can use the buttons fileOpen Load color map from file or fileSaveAs Export color map to file to load an existing color table or to save the defined color table for other sessions.

In the right block, Generate new color map allows you to create newly categorized color maps. For the Classification mode selectString ‘Equal interval’, you only need to select the number of classes selectNumber and press the button Classify. You can invert the colors of the color map by clicking the checkbox Invert checkbox. In the case of the Mode selectString ‘Continuous’, QGIS creates classes automatically depending on the Min and Max. Defining Min/Max values can be done with the help of the Load min/max values section. A lot of images have a few very low and high data. These outliers can be eliminated using the radioButtonOn Cumulative count cut setting. The standard data range is set from 2% to 98% of the data values and can be adapted manually. With this setting, the gray character of the image can disappear. With the scaling option radioButtonOff Min/max, QGIS creates a color table with all of the data included in the original image (e.g., QGIS creates a color table with 256 values, given the fact that you have 8 bit bands). You can also calculate your color table using the radioButtonOff Mean +/- standard deviation x selectNumber. Then, only the values within the standard deviation or within multiple standard deviations are considered for the color table.

Representação das cores

Em cada Representação da banda, é possível encontrar uma Representação da cor

You can also achieve special rendering effects for your raster file(s) using one of the blending modes (see Modos de Mistura).

Further settings can be made in modifying the Brightness, the Saturation and the Contrast. You can also use a Grayscale option, where you can choose between ‘By lightness’, ‘By luminosity’ and ‘By average’. For one hue in the color table, you can modify the ‘Strength’.

Reamostragem

A opção Reamostragem, faz a representação da imagem quando se dá mais ou menos zoom nela. Os modos de reamostragem podem melhorar a apariência do mapa. Eles calculam um novo valor de cinza através de uma transformação geométrica.

../../../_images/rasterRenderAndRessampling.png

Raster Style - Color rendering and Resampling settings

Quando aplicamos o método ‘Vizinho mais próximo’, o mapa pode ter uma estrutura tipo pixelada, quando damos mais zoom. Essa apariència pode ser melhorada usando os métodos ‘Bilinear’ ou ‘Cúbico’., o qual causa que as feições mais afiadas, se suavizem.

At the bottom of the Style tab, you can see a thumbnail of the layer, its legend symbol, and the palette.

Transparency Properties

QGIS has the ability to display each raster layer at a different transparency level. Use the transparency slider slider to indicate to what extent the underlying layers (if any) should be visible though the current raster layer. This is very useful if you like to overlay more than one raster layer (e.g., a shaded relief map overlayed by a classified raster map). This will make the look of the map more three dimensional.

Additionally, you can enter a raster value that should be treated as NODATA in the Additional no data value option.

Uma maneira ainda mais flexível de modificar a banda de transparência poder ser feita no :guilabel: Modificações das opções de transparência. Aqui podemos definir a transparência de cada pixel.

As an example, we want to set the water of our example raster file landcover.tif to a transparency of 20%. The following steps are necessary:

  1. Carregar o arquivo raster: Arquivo:landcover.tif.

  2. Abra o diálogo Propriedades fazendo clique duplo no nome do raster na legenda, o clicando com botão e selecionando:Propriedades do menu pop-up.

  3. Select the Transparency tab.
  4. From the Transparency band drop-down menu, choose ‘None’.
  5. Click the signPlus Add values manually button. A new row will appear in the pixel list.
  6. Entre o valor raster na coluna ‘De’ e ‘Até’ (usamos 0 aqui), e ajuste a transparência a 20%.

  7. Pressione o botão [Aplicar] e visualize no mapa as modificações feitas.

Podemos repetir os passos 5 e 6 para definir mais valores com a transparência desejada.

As you can see, it is quite easy to set custom transparency, but it can be quite a lot of work. Therefore, you can use the button fileSave Export to file to save your transparency list to a file. The button fileOpen Import from file loads your transparency settings and applies them to the current raster layer.

Pyramids Properties

Large resolution raster layers can slow navigation in QGIS. By creating lower resolution copies of the data (pyramids), performance can be considerably improved, as QGIS selects the most suitable resolution to use depending on the level of zoom.

Você deve pode ter direito de gravação no diretório onde os dados originais são armazenados para construir pirâmides.

From the Resolutions list, select resolutions for which you want to create pyramid by clicking on them.

If you choose Internal (if possible) from the Overview format drop-down menu, QGIS tries to build pyramids internally.

Nota

Note que o cálculo de pirâmides pode modificar o arquivo original de dados, e uma vez criado, não pode ser apagado. Se deseja preservar uma versão ‘sem pirâmides’ de seu raster, faça uma copia de segurança antes do cálculo das pirâmides.

If you choose External and External (Erdas Imagine) the pyramids will be created in a file next to the original raster with the same name and a .ovr extension.

Several Resampling methods can be used to calculate the pyramids:

  • Vizinho mais próximo

  • Média

  • Gauss
  • Cúbico

  • Modo

  • Nenhum

Finally, click [Build pyramids] to start the process.

../../../_images/rasterPyramids.png

Raster Pyramids

Histogram Properties

The Histogram tab allows you to view the distribution of the bands or colors in your raster. The histogram is generated automatically when you open the Histogram tab. All existing bands will be displayed together. You can save the histogram as an image with the fileSave button. With the Visibility option in the actionRun Prefs/Actions menu, you can display histograms of the individual bands. You will need to select the option radioButtonOff Show selected band. The Min/max options allow you to ‘Always show min/max markers’, to ‘Zoom to min/max’ and to ‘Update style to min/max’. With the Actions option, you can ‘Reset’ and ‘Recompute histogram’ after you have chosen the Min/max options.

../../../_images/rasterHistogram.png

Raster Histogram

Metadata Properties

The Metadata tab displays a wealth of information about the raster layer, including statistics about each band in the current raster layer. From this tab, entries may be made for the Description, Attribution, MetadataUrl and Properties. In Properties, statistics are gathered on a ‘need to know’ basis, so it may well be that a given layer’s statistics have not yet been collected.

../../../_images/rasterMetadata.png

Raster Metadata

Legend Properties

The Legend tab provides you with a list of widgets you can embed within the layer tree in the Layers panel. The idea is to have a way to quickly access some actions that are often used with the layer (setup transparency, filtering, selection, style or other stuff...).

By default, QGIS provides transparency widget but this can be extended by plugins registering their own widgets and assign custom actions to layers they manage.