[Qgis-user] Dynamic Line
L.W.
eaglelw at gmx.de
Sat Nov 21 02:48:26 PST 2020
Hi,
I do not know why exactly, but now it is working.
thanks to everyone who helped!
regards
Am 14.11.2020 um 21:50 schrieb Nicolas Cadieux:
>
> Start by joining both files using a common field (right click
> property/joins).
>
> This could give you a file that looks like this:
>
> fid,x1,y1,x2,y2
> 1,0,0,1,1
> 2,10,10,100,100
> ...
>
> Save this file as geopackage (line). This way, you can modify it.
>
> x1,y1 are from the first file and x2,y2 are from the second file.
> These coordinates can be generated by creating a new field and
> updating it with $x or $y functions in the field calculator.
>
> Then, using the field calculator, select "modify and existing field"
> and select <geometry>. Update this field using the following line.
>
> geom_from_wkt('LINESTRING(' || "x1" || ' ' || "y1" || ',' ||
> "x2" || ' ' || "y2" || ')')
>
> This will create the lines.
>
> Nicolas
>
> On 2020-11-14 7:53 a.m., L.W. wrote:
>>
>> I tried a lot ...
>>
>> I have a point-layer, I put this code in symbol -> single symbol ->
>> geometrygenerator
>>
>> What is wrong?
>>
>>
>> geom_to_wkt
>> (
>> make_line
>> (
>> make_point
>> (
>> 5826542.703128459,
>> 797907.3304607988
>> ),
>> make_point
>> (
>> 5827473.536854242,
>> 796987.0074038045
>> ),
>> make_point
>> (
>> 5827167.893279332,
>> 795128.2317764781
>> ),
>> make_point
>> (
>> 5826835.7783904355,
>> 793227.8583700341
>> )
>> )
>> )
>>
>> Am 13.11.2020 um 15:24 schrieb Andreas Neumann:
>>>
>>> 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
>>>> <https://en.wikipedia.org/wiki/Well-known_text_representation_of_geometry>
>>>>
>>>> Nicolas Cadieux
>>>>
>>>>> Le 13 nov. 2020 à 09:07, Andreas Neumann <a.neumann at carto.net> a
>>>>> écrit :
>>>>>
>>>>>
>>>>>
>>>>> 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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