What is the difference between geometry() and $geometry in QGIS?
I didn't find any examples of using this function.
Particularly I'm interested in geometry(), in what cases it is helpful?
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2 Answers
Right next to the list of functions your screenshot is of, should be the currently selected function's documentation. For me, with QGIS 2.18.12 those read:
$geometry Returns the geometry of the current feature. Can be used for processing with other functions.
geometry() Returns a feature's geometry.
This is like the different of a method versus a function in object-oriented programming. $geometry is this/self's geometry. You can think of it more like an attribute or property maybe.
geometry() on the other hand requires/allows you to pass a feature to it and it will return the corresponding geometry. As the documentation shows, you can use this to get the geometry from an attribute-based feature selection:
geometry(
get_feature(layer, attributeField, value)
)
What else you can do with it is just limited by your creativity and the sources for features to pass to it. :)
answered Aug 24, 2017 at 8:37
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So, how I can use it when trying to transform separate points that forms line ( (make_line( make_point( "xlbl" -1000, "ylbl" ), make_point(( "xlbl"+ length( ( "time" ))*3000+7000 ) , "ylbl" ),) ... etc I mean that I want to transform every point of line, based on coordinates in attribute table values– JaneCommented Aug 24, 2017 at 9:43
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I suppose I have to represent every point of my line (from make_point func) as geometry, then transform it, so far as the whole constructed geometry make_line transforms wrong gis.stackexchange.com/questions/253002/…– JaneCommented Aug 24, 2017 at 9:46
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Sure thing. This sounds like using the wrong tool though, have you tried the points2one plugin or some other processing? Commented Aug 24, 2017 at 9:53
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1No, this is a style of the layer, I can't use any plugins in layer properties. I try to solve my problem by dint of qgis built-in functions– JaneCommented Aug 24, 2017 at 10:05
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2The property comparison sounds good but the OO comparison is a bit weak,
$geometryis rather a (const) variable, regardless if OO or not. Commented Aug 24, 2017 at 12:59
$geometry returns the geometry of the current feature as in:
geom_to_wkt($geometry)
geometry() returns the geometry of a specific feature as in
geom_to_wkt(geometry(get_feature('my_layer', 'my_feature', feature_id)))
You would use the second case if you wanted, for example, to process the current feature against a specific feature:
intersects($geometry, geometry(get_feature(layer, attributeField, value)))
