QGIS on Mac WKT import problem

Question

QGIS 1.8.0 Mac OSX 10.6.8 These problems seem to be specific to Mac, as two Windows users don't have the problem.

Import a file as a vector:
TEST.CSV

id;wkt  
1;"POLYGON((10 10,20 20,20 30,20 10))"  
...  

The features import with correct values, individual points can be edited, and the layer saved as a shape file. But, no feature can be selected that was imported this way, so they can't be moved. New features added manually to the same layer can be selected and moved normally.

Probably related, only wkt-created features fully contained within the view are shown, wkt-features that have even a small bit outside the view vanish entirely. However, features added manually to the layer behave normally by showing the portion in the view. Layer editing capabilities are normal (full).

Has anyone suggestions as to a workaround for this? I'm hoping to migrate a dozen maps with 10,000 or so features from an old package that only exports true CSV:
x1,y1
x2,y2
...
I can script-edit this format to the above WKT, or similar text format. I don't have an app for .dbf so haven't been able to look there for any difference between WKT imports and QGIS-created features.

Answer 1

This is not a problem of MAC OS X or Windows, but a problem of your WKT geometry which is not valid. You can check it with the extension QuickWKT:

and the result is:

or independently of QGIS in Python with the module Shapely

from shapely.wkt import loads
wkt = loads('POLYGON((10 10,20 20,20 30,20 10))')
Traceback (most recent call last):
.....
"Could not create geometry because of errors while reading input."
 shapely.geos.ReadingError: Could not create geometry because of errors while reading input.

Why, because a polygon must be closed:

POLYGON((10 10,20 20,20 30,20 10,10 10)), for example

and the result is

and in Python with the module Shapely:

wkt = loads('POLYGON((10 10,20 20,20 30,20 10,10 10))')
list(wkt.exterior.coords)
[(10.0, 10.0), (20.0, 20.0), (20.0, 30.0), (20.0, 10.0), (10.0, 10.0)]

The expression is valid for a LINESTRING(10 10,20 20,20 30,20 10)

Answer 2

For everybody, the Plain Geometry Editor plug-in in action, clicking on a point of one of the geometries in Edit mode:

and you can change the WKT chain

But if I try with your original geometry