[Qgis-user] Dynamic Line

Fri Nov 13 06:24:41 PST 2020

Hi Nicolas,

Yes - but that doesn't magically turn a "non geometry" table into a 
"geometry table" - as far as I know. So you probably need to create a 
"Virtual Layer" and create the geometry similar to what you propose.

Andreas

Am 13.11.20 um 15:22 schrieb Nicolas Cadieux:
> Hi,
> You can create a geometry from WKT if you have x and y fields using 
> and expression in the field calculator.
> |geom_from_wkt('POINT('||"x"||' '||"y"||')')|
>
> https://en.wikipedia.org/wiki/Well-known_text_representation_of_geometry
>
> Nicolas Cadieux
>
>> Le 13 nov. 2020 Ã  09:07, Andreas Neumann <a.neumann at carto.net> a Ã©critÂ :
>>
>> ï»¿
>>
>> Hi
>>
>> Neither GeometryGenerators nor Vector Field Markers work on tables 
>> without geometry, unfortunately. You didn't inform us, that you don't 
>> have geometry in your table.
>>
>> You can, however, create a "Virtual Layer" and write some SQL to 
>> create a geometry from your attributes: menu "Layer" --> "Create 
>> Layer" --> "New Virtual Layer" - where you can use your existing 
>> tables and create a new geometry column with SQL. See 
>> https://docs.qgis.org/testing/en/docs/user_manual/managing_data_source/create_layers.html#creating-virtual-layers
>>
>> Or, if your table is a CSV file, then you can assign attribute 
>> columns to a point geometry and then just hide the point rendering if 
>> you don't need it.
>>
>> This is an unfortunate limitation of QGIS, that there is no "easy" 
>> way to add a geometry column to table that doesn't have geometry (or 
>> if it is possible, then I don't know it).
>>
>> Hope this helps you,
>>
>> Andreas
>>
>> Am 13.11.20 um 14:52 schrieb L.W.:
>>>
>>> Does it works on Layers with no geometry?
>>>
>>> My layers do not have a geometry.
>>>
>>>
>>> Am 13.11.2020 um 11:56 schrieb Andreas Neumann:
>>>>
>>>> Yes, you need point data to start from, but then vectors can 
>>>> bei/are generated from the attributes you mentioned.
>>>>
>>>> Andreas
>>>>
>>>> Am 13.11.20 um 11:47 schrieb L.W.:
>>>>>
>>>>> from the docs ...
>>>>>
>>>>> ****It can only be used to render point data****
>>>>>
>>>>>
>>>>>         12.2.2.2.6.The Vector Field Marker
>>>>>         <https://docs.qgis.org/3.10/en/docs/user_manual/style_library/symbol_selector.html?#id15>
>>>>>
>>>>> The vector field marker is used to display vector field data such 
>>>>> as earth deformation, tidal flows, and the like. It displays the 
>>>>> vectors as lines (preferably arrows) that are scaled and oriented 
>>>>> according to selected attributes of data points. ****It can only 
>>>>> be used to render point data****; line and polygon layers are not 
>>>>> drawn by this symbology.
>>>>>
>>>>> The vector field is defined by attributes in the data, which can 
>>>>> represent the field either by:
>>>>>
>>>>>  *
>>>>>
>>>>>     *cartesian*components (|x|and|y|components of the field)
>>>>>
>>>>>  *
>>>>>
>>>>>     or*polar*coordinates: in this case, attributes
>>>>>     define|Length|and|Angle|. The angle may be measured either
>>>>>     clockwise from north, or Counterclockwise from east, and may
>>>>>     be either in degrees or radians.
>>>>>
>>>>>  *
>>>>>
>>>>>     or as*height only*data, which displays a vertical arrow scaled
>>>>>     using an attribute of the data. This is appropriate for
>>>>>     displaying the vertical component of deformation, for example.
>>>>>
>>>>> The magnitude of field
>>>>>
>>>>>
>>>>> Am 13.11.2020 um 11:34 schrieb Andreas Neumann:
>>>>>> Or even easier: use the "Vector Field Marker":
>>>>>>
>>>>>> https://docs.qgis.org/3.10/en/docs/user_manual/style_library/symbol_selector.html?#the-vector-field-marker 
>>>>>>
>>>>>>
>>>>>> Am 13.11.20 um 11:33 schrieb Andreas Neumann:
>>>>>>> Hi,
>>>>>>>
>>>>>>> Yes - you can use Geometry Generators for that. Use the 
>>>>>>> make_point() and make_line() expressions for that.
>>>>>>>
>>>>>>> See 
>>>>>>> https://docs.qgis.org/3.10/en/docs/user_manual/style_library/symbol_selector.html?highlight=geometry%20generator#the-geometry-generator
>>>>>>>
>>>>>>> Greetings,
>>>>>>> Andreas
>>>>>>>
>>>>>>> Am 13.11.20 um 11:26 schrieb L.W.:
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>> is it possible to draw automatically a line between two points 
>>>>>>>> defined
>>>>>>>> by 4 fields (x1,y1 - x2,y2) in an attributetable?
>>>>>>>>
>>>>>>>> but I do not want to add a line-layer based on this table nor 
>>>>>>>> want to
>>>>>>>> draw the line by hand.
>>>>>>>>
>>>>>>>> thanks
>>>>>>>>
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