QGIS – Transforming Points into Graduated Segments in QGIS Using Geometry Generator

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In QGIS 3.16 I've got a point layer for several sample points in a coastal stretch. The attribute "EPR0113_er" indicates the erosion rate recorded at that point and I would like to represent it, not as a point, but as a segment whose length is related to the "EPR0113_er" value.

I've been trying different approaches using the Geometry Generator tool, without success. Any ideas about how to build it?

Best Answer

You can use wedge buffer:

wedge_buffer($geometry, 120, 10, "rate", 0)

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You can take care of this before ever trying to load the data into ArcGIS by creating a schema.ini file. Simply use a text editor to save a file called schema.ini (no other extension) in the same folder as your CSV. Then, explicitly specify the data types for columns that you don't want ArcGIS to infer.

For example, if your CSV were called mydata.csv and the 4th column were the one ArcGIS is loading as text, your schema.ini would look like this:

[mydata.csv]
ColNameHeader=True
Format=CSVDelimited
Col4=BG10 Long

ArcGIS always checks schema.ini files, and will therefore always correctly load the column as an integer if that is how you've specified it. If multiple CSV files are present in the same folder, they can all be controlled from the same schema.ini.

QGIS – Drawing Rectangle with Specific Size from Attribute Table

@iant was faster but this is my version with PostGIS.

This one works with points and fixed offsets "1" to each direction.

select ST_GeomFromText('POLYGON (('
 ||ST_X(the_geom)-1||' '||ST_Y(the_geom)-1||','
 ||ST_X(the_geom)-1||' '||ST_Y(the_geom)+1||','
 ||ST_X(the_geom)+1||' '||ST_Y(the_geom)+1||','
 ||ST_X(the_geom)+1||' '||ST_Y(the_geom)-1||','
 ||ST_X(the_geom)-1||' '||ST_Y(the_geom)-1||'))')
from my_points;

This is using centroids and work with any geometry type:

select ST_GeomFromText('POLYGON (('
  ||ST_X(ST_Centroid(the_geom))-1||' '||ST_Y(ST_Centroid(the_geom))-1||','
  ||ST_X(ST_Centroid(the_geom))-1||' '||ST_Y(ST_Centroid(the_geom))+1||','
  ||ST_X(ST_Centroid(the_geom))+1||' '||ST_Y(ST_Centroid(the_geom))+1||','
  ||ST_X(ST_Centroid(the_geom))+1||' '||ST_Y(ST_Centroid(the_geom))-1||','
  ||ST_X(ST_Centroid(the_geom))-1||' '||ST_Y(ST_Centroid(the_geom))-1||'))')
from my_polygons;

If your offsets are stored into attributes "offset_x" and "offset_y" use this:

select ST_GeomFromText('POLYGON (('
  ||ST_X(ST_Centroid(the_geom))-offset_x||' '||ST_Y(ST_Centroid(the_geom))-offset_y||','
  ||ST_X(ST_Centroid(the_geom))-offset_x||' '||ST_Y(ST_Centroid(the_geom))+offset_y||','
  ||ST_X(ST_Centroid(the_geom))+offset_x||' '||ST_Y(ST_Centroid(the_geom))+offset_y||','
  ||ST_X(ST_Centroid(the_geom))+offset_x||' '||ST_Y(ST_Centroid(the_geom))-offset_y||','
  ||ST_X(ST_Centroid(the_geom))-offset_x1||' '||ST_Y(ST_Centroid(the_geom))-offset_y||'))')
from my_polygons;

Best Answer

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