Extract x, y, z of all the nodes / vertices of a single polygon shapefile into a text file

Question

I want to save all the x, y, z coordinates of all the nodes (vertices) of a polygon shapefile to a text file using Python programming in QGIS Python Console.

import ogr, os, sys
fn = r'E:\Sreeraj\Thailand\Level 0\Thailand.shp'
driver = ogr.GetDriverByName('ESRI Shapefile')
ds = ogr.Open(fn) 
numLayers = ds.GetLayerCount()
print 'The file contains ', numLayers, ' Layers'
layer = ds.GetLayer(0)
print layer.GetName(), ' contains ', layer.GetFeatureCount(), ' features'
f=layer.GetFeatureCount()
v=0
s=1
file = open(r'E:\Sreeraj\Thailand\Thailand_Level 0.txt','w')
file.write('Sl No' '\t' 'X' '\t' 'Y' '\t' 'Z' '\t' 'Polygon ID' '\n')
for v in range(f):
    feature= layer.GetFeature(v)
    geometry= feature.GetGeometryRef()
    print ' Feature contains the Geometry', geometry.GetGeometryName()
    print ' It contains', geometry.GetGeometryCount(), geometry.GetGeometryName()
    ring = geometry.GetGeometryRef(r)
    print geometry.GetGeometryName(), ' contains the Geometry', ring.GetGeometryName()
    print ' It contains', ring.GetPointCount(), ' points in a ', ring.GetGeometryName()
    pointsX = []; pointsY = []; pointsZ = []
    numpoints = ring.GetPointCount()
    for p in range(numpoints):
        lon, lat, z = ring.GetPoint(p)
        pointsX.append(lon)
        pointsY.append(lat)
        pointsZ.append(z)
        x = [str(s), '\t', str(lon), '\t', str(lat), '\t', str(z), '\t', str(v), '\n']
        file.writelines(x)
        s=s+1

So, I have given above the complete python code. This is perfectly working for extracting the nodes / vertices of Thailand states, districts, etc.

But, when I have a shapefile (here, Thailand.shp) with only 1 single polygon, that is the country boundary; then this code is not working. I am not getting any error, but I am also not getting the output x, y, z coordinates of each node of this particular country boundary shapefile which is just a single polygon.

Given below is the output which I am getting.

The file contains  1  Layers
Thailand  contains  1  features
Feature contains the Geometry MULTIPOLYGON
It contains 595 MULTIPOLYGON
MULTIPOLYGON  contains the Geometry POLYGON
It contains 0  points in a  POLYGON

And I am getting the text file output which is empty.

This above python code is not working only in the case of country boundary shapefile (single polygon). If I take a shapefile with all the states, districts of Thailand; then the above code is working.

When I tried this same code for the states shapefile, I got the given below output and all the x,y,z values of all the nodes were saved in the output text file.

The file contains  1  Layers
THA_Adm1_GISTA_plyg_v5  contains  77  features
Feature contains the Geometry MULTIPOLYGON
It contains 2 MULTIPOLYGON
MULTIPOLYGON  contains the Geometry POLYGON
It contains 0  points in a  POLYGON
Feature contains the Geometry POLYGON
It contains 1 POLYGON
POLYGON  contains the Geometry LINEARRING
It contains 25015  points in a  LINEARRING
Feature contains the Geometry POLYGON
It contains 1 POLYGON
POLYGON  contains the Geometry LINEARRING
It contains 16116  points in a  LINEARRING
Feature contains the Geometry POLYGON
It contains 1 POLYGON
POLYGON  contains the Geometry LINEARRING
It contains 41120  points in a  LINEARRING
Feature contains the Geometry POLYGON
It contains 1 POLYGON
POLYGON  contains the Geometry LINEARRING
It contains 33636  points in a  LINEARRING
Feature contains the Geometry POLYGON
It contains 1 POLYGON
POLYGON  contains the Geometry LINEARRING
It contains 16774  points in a  LINEARRING
Feature contains the Geometry POLYGON
It contains 1 POLYGON
POLYGON  contains the Geometry LINEARRING
It contains 19105  points in a  LINEARRING
Feature contains the Geometry MULTIPOLYGON
It contains 155 MULTIPOLYGON
MULTIPOLYGON  contains the Geometry POLYGON
It contains 0  points in a  POLYGON
Feature contains the Geometry POLYGON
It contains 1 POLYGON
POLYGON  contains the Geometry LINEARRING
It contains 8501  points in a  LINEARRING
..........................................................
// and many lines of outputs like this. This is correct. 

But for the boundary shapefile (single polygon), I am not getting output.

Answer 1

The solution to this issue is to use the Multiparts to Singleparts tool in order to convert the curent multipolygon boundary shapefile to a polygon shapefile. Then take this output shapefile of the country boundary as the input to the python program. Then, the python program will get executed properly.