Janela das Propriedades da Camada Raster¶

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.

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 continous 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:

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 Estimate (faster) the Min and Max values of the bands or use the 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 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 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 Mean +/- standard deviation x . 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 Current extent.

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 2.2. it’s now possible to assign a label to the color values. The label appears in the legend of the raster layer then.

Figure Raster 3:

Raster Renderer - Paletted

Melhorar contraste

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 Estimate (faster) the Min and Max values of the bands or use the Actual (slower) Accuracy.

Figure Raster 4:

Raster Renderer - Singleband gray

With the Load min/max values section, scaling of the color table is possible. Outliers can be eliminated using the 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 Min/max and Mean +/- standard deviation x . 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 continous palette. You can also create individual color maps for the single bands here.

Figure Raster 5:

Raster Renderer - Singleband pseudocolor

Três tipos de interpolação de cores estão disponíveis:

1. Discreto

2. Linear

3. Exacto

In the left block, the button ^{Add values manually} adds a value to the individual color table. The button ^{Remove selected row} deletes a value from the individual color table, and the ^{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 ^{Load color map from band}, which tries to load the table from the band (if it has any). And you can use the buttons ^{Load color map from file} or ^{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 ‘Equal interval’, you only need to select the number of classes and press the button Classify. You can invert the colors of the color map by clicking the Invert checkbox. In the case of the Mode ‘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 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 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 Mean +/- standard deviation x . 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 modifiying 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:

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.