[GIS] QGIS Atlas turning on/off raster layers

atlasqgisraster

I'm attempting to create a series of maps in QGIS atlas with the same coverage and background data but different raster outputs (flood mapping outputs for a range of scenarios).

I've created a shapefile coverage layer containing polygons for each of the scenarios and using the polygon identifier attempted to turn on and off raster layers using a function within a label object. I've played around with the function for a while but can't get it to work…

Does this sound like the right approach that I'm taking? Is there a better way to do this?

I'm very much a beginner when it comes to using functions in QGIS.

Best Answer

I've just done this with 84 different raster layers. The method i used was:

Create an atlas polygons layer with 84 features in it.
Create a text field in the atlas polygons layer and write the names of all of the layers you want that atlas map to show, separated by the | character. For examle: If you wanted to show three fields: "flood_results","Background_mapping" and "Vector_layer" then your field would contain this string: flood_results|Background_mapping|Vector_layer
Assign your atlas polygons in the Atlas Generation tab
In the print composer, the item properties for the map view window: there is a lock layers for map item checkbox with a data-defined override field option, make this field your text field with the layers in.

Now as you cycle through your atlas maps, the layers will change depending on the layers specified in the layers field of each atlas polygon.

Related Solutions

[GIS] How to extract values from a raster using R

The mean and standard deviation can be calculated using cellStats() from the raster package.

#install.packages(raster)
library(raster)

# example dataset
r <- raster(nrow=18, ncol=36)
r[] <- runif(ncell(r)) * 10

# get mean
cellStats(r,'mean')

QGIS Atlas Error – Fixing Eval Error When Selectively Rendering Raster Layers

I have not tested your function, but the Eval Error you are seeing is because QGIS custom functions take additional feature and parent parameters. This is explained in the help section of the function editor shown below:

And quoted directly here:

Define a new function using the @qgsfunction decorator.

The function accepts the following parameters

: param [any]: Define any parameters you want to pass to your function before the following arguments.
: param feature: The current feature
: param parent: The QgsExpression object
: param context: If there is an argument called context found at the last position, this variable will contain a QgsExpressionContext object, that gives access to various additional information like expression variables. E.g. context.variable( 'layer_id' )
: returns: The result of the expression.

Therefore, you should add feature and parent parameters to your custom function after your str_to_match parameter.

...
@qgsfunction(args='auto', group='Custom')
def find_match_fun(str_to_match, feature, parent):
...

You can also have a look at this helpful tutorial:

Best Answer

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[GIS] How to extract values from a raster using R

QGIS Atlas Error – Fixing Eval Error When Selectively Rendering Raster Layers

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