This may be trivial question, but I'm confused, 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?
Add a comment
|
2 Answers
Right next to the list of functions your screenshot is of, should be the currently selected function's documentation. For me, with 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 a 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
-
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– JaneAug 24, 2017 at 9:43
-
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/…– JaneAug 24, 2017 at 9:46
-
Sure thing. This sounds like using the wrong tool though, have you tried the points2one plugin or some other processing? Aug 24, 2017 at 9:53
-
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– JaneAug 24, 2017 at 10:05
-
2The property comparison sounds good but the OO comparison is a bit weak,
$geometryis rather a (const) variable, regardless if OO or not. 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)))
