QGIS – How to Create Multiple QGIS Layers from Multiple Text Files

batchlayerspyqgisqgistext;

I have a few hundred txt files (each representing a line of a river bed profile) that I need to load as (point-) layers in QGIS. Partial example:

4504764.8331;5374251.3024;397.8871;2
4504764.7761;5374250.8056;397.8555;2
4504764.7191;5374250.3089;397.8295;2
4504764.6621;5374249.8121;397.8149;2
4504764.6051;5374249.3154;397.7977;2
4504764.5481;5374248.8186;397.7725;2

It works manually (layer -> add delimited text layer, then renaming the columns after import) but given the volume I can't do it all by hand.

I found a similar two year old question here: How to import multiple textfiles in one step , but "create a plain text file called .vrt file for each of csv files" doesn't sound so peachy. The files are also missing the header line, but I know the format: "X; Y; Z; classification".

Is there any way to do this without having to code up a text generator for those vrt files and inserting header lines into all csvs?

Best Answer

Assuming all your text files are into the same directory, you can run this code snippet in the QGIS Python console to get your files loaded as individual layers in QGIS:

import os.path, glob
layers=[]
for file in glob.glob('/tmp/xy/*.txt'): # Change this base path
  uri = "file:///" + file + "?delimiter=%s&xField=%s&yField=%s&useHeader=no&crs=epsg:3116" % (";", "field_1","field_2")
  vlayer = QgsVectorLayer(uri, os.path.basename(file), "delimitedtext")
  vlayer.addAttributeAlias(0,'X')
  vlayer.addAttributeAlias(1,'Y')
  vlayer.addAttributeAlias(2,'Z')
  vlayer.addAttributeAlias(3,'classification')
  layers.append(vlayer)

QgsMapLayerRegistry.instance().addMapLayers(layers)

As you see, it works for GNU/Linux paths, I don't know how the uri (specifically the file path) should look like for Windows. Also, adjust the crs for your own case.

I also wanted to tell you how to change field names automatically, but it seems that delimited-text based layers cannot be edited. I guess the most you can do is to assign aliases for your columns, as the code does.

Related Solutions

QGIS Atlas – How to Use with Multiple Layers or Files per Coverage

Since QGIS 2.12, with the introduction of data-defined properties on the "lock layers for map" option, in the map item properties, you can do what you seek. You just need to create the right coverage layer, with the information of the extents, but also of the layers to "print".

Create the layer presets

You can "save" the current state (visible or not visible) of your layers as presets. Just create the desired combination and press the eye icon on the layers panel, and choose "add preset".

Basically, you will have to create a preset for each contour, with that layer visible (paired with other layers if you like). This will be your "set of layers".

Give your preset memorable names, or else just opt for some kind of a sequence.

Creating the coverage layer.

Now you will have to create a polygon layer with all the possible combinations between the extents polygons, and all the presets. That means you will end up with some redundancy. You will have to replicate each extent polygon for each preset. Something like this:

polygon 1, preset a polygon 1, preset b ... polygon 50, preset a polygon 50, preset b

You can do this manually with copy paste, or else create some kind of script, but I would say your best and easier way would be using Spatialite or Postgis database. Just import you polygons extents there, and create a new non-spatial table with all presets names. Then, create a view that returns all the combinations.

SELECT f.*, g.preset_name
FROM polygons_extent as f, presets as g

Making it work

Add the new layer or view to QGIS, use it as coverage layer in atlas settings, and use the preset_name attribute in data-defined properties on the "lock layers for map" option.

[GIS] QGIS create a new merged layer from selection on multiple layers

You could use a bit of Python to get the selected features from multiple layers and save them to a new shapefile:

First select your features from your layers.

In the Python Console, run the following code to define a function which iterates through each layer and saves the selected features into a memory layer which is finally saved as a shapefile (edit the code to change the path of the output):

def run(name, crs):
    # To create polygon memory layer, use "Polygon"; "Point" for point layer; "LineString" for line layer
    mem_layer = QgsVectorLayer("Polygon?crs=epsg:" + str(crs), "Layer_Name", "memory")
    mem_layer.startEditing()
    for layer in QgsMapLayerRegistry.instance().mapLayers().values():
        attr = layer.dataProvider().fields().toList()
        mem_layer.dataProvider().addAttributes(attr)
        mem_layer.updateFields()
        feats = [ feat for feat in layer.selectedFeatures() ]           
        mem_layer.dataProvider().addFeatures(feats)
    mem_layer.commitChanges()
    path = r"path/to/directory/" + name
    new_layer = QgsVectorFileWriter.writeAsVectorFormat(mem_layer, path, "utf-8", None, "ESRI Shapefile")
    del mem_layer
    QgsMapLayerRegistry.instance().addMapLayer(QgsVectorLayer(path + ".shp", name, "ogr"))

Then run the following to execute the function where, for example, the output shapefile name is "merged" and its CRS set at ESPG:27700:
```
run('merged', 27700)
```

Best Answer

Related Solutions

QGIS Atlas – How to Use with Multiple Layers or Files per Coverage

[GIS] QGIS create a new merged layer from selection on multiple layers

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