Outdated version of the documentation. Find the latest one here.

Janela das Propriedades da Camada Raster

Para visualizar e definir as propriedades da camada raster, dê um duplo clique no nome da camada na legenda do mapa, ou clique com o botão direito no nome da camada e escolha:Propriedades a partir do menu de contexto. Irá abrir o diálogo Propriedades da Camada Raster (see figure_raster_1).

Existem vários menus na caixa de diálogo:

  • Geral

  • Estilo

  • Transparência

  • Pirâmides

  • Histograma

  • Metadados

Figure Raster 1:

../../../_images/rasterPropertiesDialog.png

Raster Layers Properties Dialog

Menu Geral

Informação da camada

O menu General apresenta informações básicas sobre a imagem selecionada, incluindo o caminho da origem da camada, o nome de exibição na legenda (que pode ser modificado), e o número de colunas, linhas e valores nulos do raster.

Sistema de Referência de Coordenadas

Aqui, pode encontrar a informação do sistema de referência de coordenadas (SRC) impressos numa sequência PROJ.4. Se essa configuração não estiver correta, ele pode ser modificada clicando no botão [Specify] .

Escala dependente da visibilidade

Além disso a visibilidade dependente da escala pode ser vista neste guia. Você terá que verificar a caixa de seleção e definir uma escala adequada, onde seus dados serão exibidos na tela do mapa.

Na parte inferior, pode ver uma miniatura da camada, a simbologia da legenda e a palete.

Estilos

Renderizar banda

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

  1. Multibanda cor - se o arquivo vem como multibanda, com várias bandas (e.g., usado para imagens de satelite com várias bandas)

  2. Palete - se o ficheiro de banda simples vem com a palete indexada (e.g., usado em 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 Simples de Pseudocor - é possível a renderização de ficheiros com uma palete continua ou de cor (e.g., usada num mapa de altitude)

Cor multibanda

Com o renderizador da cor multibanda, as três bandas da imagem pode ser renderizada, pela banda que representa o componente vermelho, verde ou azul, que será usado para criar uma imagem colorida. Pode escolher vários: Contrast enhancement methods: ‘No enhancement’, ‘Stretch to MinMax’, ‘Stretch and clip to MinMax’ and ‘Clip to min max’.

Figure Raster 2:

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

Raster Renderer - Multiband color

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.

Tip

Visualização de uma Banda Simples de um Raster Multibanda

Se quiser ver uma única banda de uma imagem multibanda (por exemplo, vermelho), pode pensar que iria definir o verde e faixas azuis para “Not Set”. Mas esta não é a maneira correta. Para apresentar a banda vermelha, defina o tipo de imagem para ‘Banda simples cinza’, em seguida, selecione vermelha como a banda para usar a Cinza.

Paletizada

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.

Figure Raster 3:

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

Raster Renderer - Paletted

Melhorar contraste

Note

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 cinza simples

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.

Figure Raster 4:

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

Raster Renderer - Singleband gray

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.

Banda de cor falsa simples

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.

Figure Raster 5:

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

Raster Renderer - Singleband pseudocolor

Três tipos de interpolação de cores estão disponíveis:

  1. Discreto

  2. Linear
  3. Exacto

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 ‘Continous’, 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.

Renderização Cor

For every Band rendering, a Color rendering is possible.

You can also achieve special rendering effects for your raster file(s) using one of the blending modes (see Janela das Propriedades da Camada Vectorial).

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

The Resampling option makes its appearance when you zoom in and out of an image. Resampling modes can optimize the appearance of the map. They calculate a new gray value matrix through a geometric transformation.

Figure Raster 6:

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

Raster Rendering - Resampling

When applying the ‘Nearest neighbour’ method, the map can have a pixelated structure when zooming in. This appearance can be improved by using the ‘Bilinear’ or ‘Cubic’ method, which cause sharp features to be blurred. The effect is a smoother image. This method can be applied, for instance, to digital topographic raster maps.

Menu Transparência

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 menu.

Uma forma ainda mais flexível para personalizar a transparência pode ser feito no: guilabel: seção de opções de transparência personalizado. A transparência de cada pixel pode ser definido aqui.

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 ficheiro raster:ficheiro:landcover.tif.

  2. Open the Properties dialog by double-clicking on the raster name in the legend, or by right-clicking and choosing Properties from the pop-up menu.
  3. Seleccionar Transparência menu

  4. No menu Transparencia da banda, escolha ‘Nenhum’.

  5. Click the signPlus Add values manually button. A new row will appear in the pixel list.
  6. Entre o valor dos raster na coluna ‘De’ e ‘Para’ (usamos 0 aqui), e ajuste a transparência a 20%.

  7. Pressione no botão [Aplicar] e olhe para o mapa

Pode repetir os passos 5 e 6 para ajustar mais valores com a transparência personalizada.

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.

Menu Pirâmides

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.

Deverá ter acesso à edição no directório onde os dados originais são armazenados para construir pirâmides.

Podem ser usados vários métodos de re-amostragem para calcular as pirâmides:

  • Vizinho mais próximo

  • Média

  • Gauss
  • Cúbico

  • moda

  • Nenhum

If you choose ‘Internal (if possible)’ from the Overview format menu, QGIS tries to build pyramids internally. You can also choose ‘External’ and ‘External (Erdas Imagine)’.

Figure Raster 7:

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

The Pyramids Menu

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

Menu Histograma

The Histogram menu allows you to view the distribution of the bands or colors in your raster. The histogram is generated automatically when you open the Histogram menu. 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.

Figure Raster 8:

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

Raster Histogram

Menu Metadados

The Metadata menu displays a wealth of information about the raster layer, including statistics about each band in the current raster layer. From this menu, 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.

Figure Raster 9:

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

Raster Metadata