Python Processing Script for Splitting Layer and Saving each Feature to Shapefile

A script for a common task: Split a Layer by distinct values of an attribute-field. The script will use the value for the name of the files and remove the field from the new files.

Put this processing script to the appropiate director (in my case it's "C:\Users\Kay\.qgis2\processing\scripts") to make it work. Then it will be easily accessible from your processing toolbox.

##[User scripts]=group
##input=vector
##class_field=field input
##output=output file

from qgis.core import *
from PyQt4.QtCore import *
from processing.core.VectorWriter import VectorWriter

layer = processing.getObject(input)
provider = layer.dataProvider()
fields = provider.fields()
class_field_index = layer.fieldNameIndex(class_field)

fields.remove( class_field_index )

inFeat = QgsFeature()
outFeat = QgsFeature()
inGeom = QgsGeometry()
nElement = 0
writers = {}

feats = processing.features(layer)
nFeat = len(feats)

for inFeat in feats:
    progress.setPercentage(int(100 * nElement / nFeat))
    nElement += 1
    featAttr = inFeat.attributes()
    classField = featAttr[class_field_index]

    if classField not in writers:
        outputFile = output + '_' + classField + '.shp'
        writers[classField] = VectorWriter(outputFile, None, fields, provider.geometryType(), layer.crs())
        
    inGeom = inFeat.geometry()
    outFeat.setGeometry(inGeom)
    
    del featAttr[class_field_index]
    outFeat.setAttributes(featAttr)
        
    writers[classField].addFeature(outFeat)

for writer in writers.values():
    del writer

QspatiaLite Use Case: Connecting Lines

With QSpatiaLIte you can connect disjoint lines quite easily. With the below SQL you can allow for a grouping variable, in this case the field 'name' within the layer 'segments', by which the group vertices are collected and connected as lines! With this approach the vertices are connected in the order in which they were digitized and existing gaps are closed.

select 
  name as name,
  makeLine(t.ptgeom, 0) as geom 
from (
     select
        name as name,
        DissolvePoints(Collect(ST_Reverse(geometry)))  as ptgeom
     from segments group by name )
as t

Usecase for KML-Parsing: Make New KML-File from File-Collection

In this usecase I had collected several KMLs from the internet but wanted to strip them down for only the relevant parts (the Linestrings inside the Placemark-nodes) and put them all inside one final File. In my script I create a new KML file and populate a folder-node inside it with Linestrings from the collection of KML-files which all reside in the same source directory. For this one needs to parse each file and grab the appropiate nodes and add them to the target kml file. In addition I alter some oroginal values, i.e. I use the file names of the single KML-files as Placemark names inside the new KML-file.

Here is the final file as seen after opening in Google Earth:

library(XML)

# new kml file... needs to be well-formed
z <-
  '<kml xmlns="http://www.opengis.net/kml/2.2">
      <Document>
         <Folder>
            <name>ROUTES</name>
         </Folder>
      </Document>
    </kml>'
new_xmlDoc <- xmlInternalTreeParse(z, useInternalNodes = TRUE)

# important add all namespace definitions...
ns <- c(gx="http://www.google.com/kml/ext/2.2",
        kml="http://www.opengis.net/kml/2.2",
        atom="http://www.w3.org/2005/Atom")
ensureNamespace(new_xmlDoc, ns)

# get the root off the new file for latter processing
new_root <- xmlRoot(new_xmlDoc)

# loop over files from folder
# and insert Placemark content of each file as children nodes into 
# the new file

setwd("C:/Users/Kay/Google Drive/SKI-BIKE/Gastein")
files <- dir(pattern="bergfex*")

for (f in files) { 
   
   # get placemark node of each file
   doc <- xmlInternalTreeParse(f, useInternalNodes = TRUE)
   root <- xmlRoot(doc)
   plcm_node <- root[["Document"]][["Folder"]][["Folder"]][["Placemark"]]

   # insert file name as Placemark name
   xmlValue(plcm_node[["name"]]) <- sub('bergfextour_(.*)[.]kml', '\\1', f)

   # add placemark node to new doc
   addChildren(new_root[["Document"]][["Folder"]], plcm_node)

}

# save it...
saveXML(new_xmlDoc, "collapsed_ROUTES.kml")