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
Nicolas Cadieux
Le 13 nov. 2020 à 09:07, Andreas Neumann <a.neum...@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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