I have 30 points, each one represents the SE corner of a 1.5 by 1.5m plot. I want to create polygons to represent these plots.
How do I create square polygons from a corner point and with a specific length?
QGIS Polygon Creation – Creating Square Polygons of Given Length from Single Corner Point in QGIS
Measurementspointpolygonpolygon-creationqgis
Related Solutions
Try this:
- Install R, and if you want a (slightly) more GUI style R-Studio
- Open R (Studio) and run this script (modify to your need) (there is an option to run it step-by-step, if you prefer):
# install dbscan package install.packages("fpc") # load library library(fpc) # set plots bg-color par(bg="grey80") # import your point data data = read.csv("/home/ymirsson/R/projects/DBSCAN_Test/point_sample.csv",sep=";",header=T) # create a working object data2=data # delete all variables you do not want to be used to cluster the points data2$ID = NULL # plot points plot(data2) # run DBSCAN clustering ds <- dbscan(data2, eps=100, MinPts=3, showplot=1) # create a vector with the cluster prediction pre <- predict(ds,data2) # join the prediction to your base data-object exp <- data.frame(data,pre) # export write.table(exp, "/home/ymirsson/R/projects/DBSCAN_Test/point_sample_clustered.txt", sep="\t")Note: The clustering will take a lot of time .. so it may be better to experiment with a smaller sample until you have your paramters for eps/min-points. - Import your clustered points in QGIS
- Select only those with "pre">0 (b/c there will be outliers, and they will screw up your polygons ;) )
- Run Vector>Geoprocessing Tools>Convex Hulls, with only your selected points and set your cluster-variable
Will look smth. like this: - You may want to extend the borders with a buffer:
or zoomed:
Please note:
- I'm not aware of a QGIS implementation of dbscan or a c&p python script .. but that doesn't mean it doesn't exist, so maybe you can skip the R part ;)
- I'm more of a "fun user" in R, and mostly for data statistics. There may be a better script and maybe you can create the polygons in R .. i don't know.
EDIT:
The surrounding borders of the convex hulls are very rough, so i propose an improvement idea:
This shows the "current" state of the resulting polygons, which include a lot of unnecessary empty space:
Idea:
In a subsequent step mark the outlining points and ID them (counter)clockwise:
Create a line vector with one of the "point 2 line/path" plugins:
And convert it into a more suitable polygon (incl. a buffer):
Comparison:
I'm not aware of a plugin to fetch the outline-points, but i think it wouldn't be that hard to write a little script.
You can use Geometry by expression.
This will create a point projected from the center point in the directions 0, 5, 10, 15, ..., 355
at 50 m distance, then draw a line from the center point and the projected point:
collect_geometries(
array_foreach(array:=generate_series( 0, 355, 5),
expression:=
make_line($geometry,
project( point:=$geometry, distance:=50, azimuth:=radians(@element)
))))
It will be a multiline, you can explode it to singlepart lines with Multipart to singleparts
Best Answer
There is "Vector geometry > Geometry by Expression" tool in Processing Toolbox. You should use in a projected coordinate system.
Select "Polygon" as "Output geometry type" option.
Click "Expression" button (highlighted blue square)
And paste the following expression
Result: