24.1.11. Análise espacial Raster (Matricial)

24.1.11.1. Exposição/Orientação de Encostas

Calculates the aspect of the Digital Terrain Model in input. The final aspect raster layer contains values from 0 to 360 that express the slope direction, starting from north (0°) and continuing clockwise.

../../../../_images/aspect.png

Fig. 24.13 Gama de valores da Exposição

A figura seguinte apresenta a camada de orientações reclassificada através de uma paleta (de cores).

../../../../_images/aspect_2.png

Fig. 24.14 Camada de Exposição reclassificada

24.1.11.1.1. Parâmetros

Label

Nome

Type

Descrição

Elevation layer

INPUT

[raster]

Digital Terrain Model raster layer

Z factor

Z_FACTOR

[number]

Default: 1.0

Vertical exaggeration. This parameter is useful when the Z units differ from the X and Y units, for example feet and meters. You can use this parameter to adjust for this. The default is 1 (no exaggeration).

Aspect

OUTPUT

[raster]

Specify the output aspect raster layer. One of:

  • Save to a Temporary Layer (TEMPORARY_OUTPUT)

  • Save to File…

The file encoding can also be changed here.

24.1.11.1.2. Resultados

Label

Nome

Type

Descrição

Aspect

OUTPUT

[raster]

The output aspect raster layer

24.1.11.1.3. Python code

Algorithm ID: qgis:aspect

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Usando os algoritmos do processamento a partir da consola for details on how to run processing algorithms from the Python console.

24.1.11.2. Sombreados

Calculates the hillshade raster layer given an input Digital Terrain Model.

O sombreado da camada é calculado de acordo com a posição do sol com a opção de escolha, quer do seu ângulo horizontal (azimute), quer do seu ângulo vertical (elevação).

../../../../_images/azimuth.png

Fig. 24.15 Azimute e ângulo vertical

A camada de sombreados compreende valores entre 0 (sombra total) até 255 (claridade total). O método dos sombreados é habitualmente utilizado para aumentar a percepção do relevo do terreno.

../../../../_images/hillshade.png

Fig. 24.16 Camada de sombreados de azimute 300 e ângulo vertical 45

É particularmente interessante atribuir à camada de sombreados um nível de transparência que possibilite sobrepô-la ao raster de altitudes:

../../../../_images/hillshade_2.png

Fig. 24.17 Sobreposição dos sombreados à camada de altitudes

24.1.11.2.1. Parâmetros

Label

Nome

Type

Descrição

Elevation layer

INPUT

[raster]

Digital Terrain Model raster layer

Z factor

Z_FACTOR

[number]

Default: 1.0

Vertical exaggeration. This parameter is useful when the Z units differ from the X and Y units, for example feet and meters. You can use this parameter to adjust for this. Increasing the value of this parameter will exaggerate the final result (making it look more «hilly»). The default is 1 (no exaggeration).

Azimuth (horizontal angle)

AZIMUTH

[number]

Default: 300.0

Set the horizontal angle (in degrees) of the sun (clockwise direction). Range: 0 to 360. 0 is north.

Vertical angle

V_ANGLE

[number]

Default: 40.0

Define o ângulo vertical (graus) ou altura do sol. Os valores variam entre 0 (altura mínima) e 90 (altura máxima).

Hillshade

OUTPUT

[raster]

Specify the output hillshade raster layer. One of:

  • Save to a Temporary Layer (TEMPORARY_OUTPUT)

  • Save to File…

The file encoding can also be changed here.

24.1.11.2.2. Resultados

Label

Nome

Type

Descrição

Hillshade

OUTPUT

[raster]

The output hillshade raster layer

24.1.11.2.3. Python code

Algorithm ID: qgis:hillshade

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Usando os algoritmos do processamento a partir da consola for details on how to run processing algorithms from the Python console.

24.1.11.3. Curvas Hipsométricas

Calculates hypsometric curves for an input Digital Elevation Model. Curves are produced as CSV files in an output folder specified by the user.

A hypsometric curve is a cumulative histogram of elevation values in a geographical area.

You can use hypsometric curves to detect differences in the landscape due to the geomorphology of the territory.

24.1.11.3.1. Parâmetros

Label

Nome

Type

Descrição

DEM to analyze

INPUT_DEM

[raster]

Digital Terrain Model raster layer to use for calculating altitudes

Boundary layer

BOUNDARY_LAYER

[vector: polygon]

Polygon vector layer with boundaries of areas used to calculate hypsometric curves

Step

STEP

[number]

Default: 100.0

Vertical distance between curves

Use % of area instead of absolute value

USE_PERCENTAGE

[boolean]

Default: False

Write area percentage to “Area” field of the CSV file instead of the absolute area

Hypsometric curves

OUTPUT_DIRECTORY

[folder]

Specify the output folder for the hypsometric curves. One of:

  • Save to a Temporary Layer (TEMPORARY_OUTPUT)

  • Save to File…

The file encoding can also be changed here.

24.1.11.3.2. Resultados

Label

Nome

Type

Descrição

Hypsometric curves

OUTPUT_DIRECTORY

[folder]

Directory containing the files with the hypsometric curves. For each feature from the input vector layer, a CSV file with area and altitude values will be created.

The file names start with histogram_, followed by layer name and feature ID.

../../../../_images/hypsometric.png

24.1.11.3.3. Python code

Algorithm ID: qgis:hypsometriccurves

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Usando os algoritmos do processamento a partir da consola for details on how to run processing algorithms from the Python console.

24.1.11.4. Relevo

Creates a shaded relief layer from digital elevation data. You can specify the relief color manually, or you can let the algorithm choose automatically all the relief classes.

../../../../_images/relief.png

Fig. 24.18 Camada de relevo

24.1.11.4.1. Parâmetros

Label

Nome

Type

Descrição

Elevation layer

INPUT

[raster]

Digital Terrain Model raster layer

Z factor

Z_FACTOR

[number]

Default: 1.0

Vertical exaggeration. This parameter is useful when the Z units differ from the X and Y units, for example feet and meters. You can use this parameter to adjust for this. Increasing the value of this parameter will exaggerate the final result (making it look more «hilly»). The default is 1 (no exaggeration).

Generate relief classes automatically

AUTO_COLORS

[boolean]

Default: False

If you check this option the algorithm will create all the relief color classes automatically

Relief colors

Opcional

COLORS

[table widget]

Use the table widget if you want to choose the relief colors manually. You can add as many color classes as you want: for each class you can choose the lower and upper bound and finally by clicking on the color row you can choose the color thanks to the color widget.

../../../../_images/relief_table.png

Fig. 24.19 Manually setting of relief color classes

The buttons in the right side panel give you the chance to: add or remove color classes, change the order of the color classes already defined, open an existing file with color classes and save the current classes as file.

Relief

OUTPUT

[raster]

Default: [Save to temporary file]

Specify the output relief raster layer. One of:

  • Save to a Temporary Layer (TEMPORARY_OUTPUT)

  • Save to File…

The file encoding can also be changed here.

Frequency distribution

FREQUENCY_DISTRIBUTION

[table]

Default: [Skip output]

Specify the CSV table for the output frequency distribution. One of:

  • Skip Output

  • Save to a Temporary Layer (TEMPORARY_OUTPUT)

  • Save to File…

The file encoding can also be changed here.

24.1.11.4.2. Resultados

Label

Nome

Type

Descrição

Relief

OUTPUT

[raster]

The output relief raster layer

Frequency distribution

OUTPUT

[table]

The output frequency distribution

24.1.11.4.3. Python code

Algorithm ID: qgis:relief

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Usando os algoritmos do processamento a partir da consola for details on how to run processing algorithms from the Python console.

24.1.11.5. Acidentado do Terreno/Índice de Rugosidade

Determina a medida quantitativa da heterogeneidade do terreno descrita por Riley et al. (1999). É calculado para cada ponto analisando as diferenças de elevação existentes na grelha de células 3x3 em cujo centro está contido (ponto).

Cada célula contêm o somatório das diferenças absolutas de elevação entre uma célula central e as oito que a envolvem.

../../../../_images/ruggedness.png

Fig. 24.20 Camada do Acidentado do Terreno desenvolvendo-se dos baixos (vermelho) para os altos (verde) índices.

24.1.11.5.1. Parâmetros

Label

Nome

Type

Descrição

Elevation layer

INPUT

[raster]

Digital Terrain Model raster layer

Z factor

Z_FACTOR

[number]

Default: 1.0

Vertical exaggeration. This parameter is useful when the Z units differ from the X and Y units, for example feet and meters. You can use this parameter to adjust for this. Increasing the value of this parameter will exaggerate the final result (making it look more rugged). The default is 1 (no exaggeration).

Ruggedness

OUTPUT

[raster]

Default: [Save to temporary file]

Specify the output ruggedness raster layer. One of:

  • Save to a Temporary Layer (TEMPORARY_OUTPUT)

  • Save to File…

The file encoding can also be changed here.

24.1.11.5.2. Resultados

Label

Nome

Type

Descrição

Ruggedness

OUTPUT

[raster]

The output ruggedness raster layer

24.1.11.5.3. Python code

Algorithm ID: qgis:ruggednessindex

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Usando os algoritmos do processamento a partir da consola for details on how to run processing algorithms from the Python console.

24.1.11.6. Declives (ângulos)

Calcula os declives (em unidades angulares) de uma dada camada raster. O declive, aqui entendido como o ângulo de inclinação do terreno, é expresso em graus.

Na figura seguinte pode ver-se à esquerda a camada DEM que contêm a elevação do terreno e à direita o cálculo dos declives:

../../../../_images/slope2.png

Fig. 24.21 Áreas planas a vermelho, áreas inclinadas a azul

24.1.11.6.1. Parâmetros

Label

Nome

Type

Descrição

Elevation layer

INPUT

[raster]

Digital Terrain Model raster layer

Z factor

Z_FACTOR

[number]

Default: 1.0

Vertical exaggeration. This parameter is useful when the Z units differ from the X and Y units, for example feet and meters. You can use this parameter to adjust for this. Increasing the value of this parameter will exaggerate the final result (making it steeper). The default is 1 (no exaggeration).

Slope

OUTPUT

[raster]

Default: [Save to temporary file]

Specify the output slope raster layer. One of:

  • Save to a Temporary Layer (TEMPORARY_OUTPUT)

  • Save to File…

The file encoding can also be changed here.

24.1.11.6.2. Resultados

Label

Nome

Type

Descrição

Slope

OUTPUT

[raster]

The output slope raster layer

24.1.11.6.3. Python code

Algorithm ID: qgis:slope

import processing
processing.run("algorithm_id", {parameter_dictionary})

The algorithm id is displayed when you hover over the algorithm in the Processing Toolbox. The parameter dictionary provides the parameter NAMEs and values. See Usando os algoritmos do processamento a partir da consola for details on how to run processing algorithms from the Python console.