[GIS] How to change vector attributes values

pyqgispythonqgis

I want to change vector attributes values.

i could not get the command fet.setAttribute
indeed, it is mentionned in http://hub.qgis.org/issues/7223 that:

"The QgsFeature instance now must be first initialized with initAttributes() to know how many attributes it will contain. Then there's setFields() call that allows doing name-to-index mapping in QgsFeature."

however, i could not get fet.initAttributes() and fet.setFields() working. (newbie…)

the error message I get is "AttributeError: 'QgsFeature' object has no attribute 'initAttributes'".

any help appreciated.

qgis version: 1.8.0

gis-python version: 1.8.0-8

python: 2.7.3-7.2

os: fedora17

Best Answer

That is the new QGIS 2.0 (not released) API. 1.8 uses a different method.

Use:

feature.changeAttribute(columnnumber, value)

or:

layer.changeAttributeValue(feature.id(), columnnumber, value)

Example:

layer.changeAttributeValue(feature.id(), 3, "Hello World")

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Here is an example:

>>> variant_string = QVariant('this is a string')
>>> variant_int = QVariant( 100)
>>> variant_string
<PyQt4.QtCore.QVariant object at 0x100f5abb0>
>>> variant_string.toString()
PyQt4.QtCore.QString(u'this is a string')
>>> str(variant_string.toString())
'this is a string'
>>> variant_int.toInt()
(100, True)

Notice that toInt() returns a tuple, the first element being the value and the second being a boolean indicating if the conversion to integer was successful.

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In QGIS, Raster -> projections -> warp calling GDAL's gdalwarp utility is the method to change the CRS of a raster file.

This is an external command, so it does not look at the project or layer CRS you might have set in QGIS.

Select the right CRS for source, and the desired for target CRS, abd give the output a different filename. You can add the result to the canvas, and check the extent in the layers properties, metadata tab. It should be different from the originals extent

Best Answer

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