Calculating line centroids for 460,000 features in QGIS?

Question

I have a large shapefile of lines, and want to run a mmqgis function (Plugins --> mmqgis --> Modify --> Convert Geometry Type.)

The problem is the file is very large and crashes the program. What options do I have?

Would running it as background python script work (and if so how do I find the commands for mmqgis function?)?

There are 460'000 features and i'm running a 3.40GHz i7 with 12GB of RAM. Is there a way of this not breaking down?

Answer 1

You might try importing the shp into postgis with shp2pgsql and running the query for ST_Centroid in the database. See the docs here.

Answer 2

To calculate the coordinates of each line segment's midpoint, create two new fields using the functions:

(x_max( $geometry ) + x_min( $geometry ))/2

and

(y_max( $geometry ) + y_min( $geometry ))/2

Answer 3

With FME Desktop, you can use this transformer: CenterOfGravityReplacer. It's very easy to use this.

Replaces the geometry of the feature with a point at the center of mass of the feature. Note that, depending on the feature’s shape, the resulting point may be far outside of the original feature.

Example The transformer calculates the exact distribution of portions of a shape; therefore, some points can actually appear outside a feature.

Answer 4

If you don't want to set up a database like zimmi suggested I would use GDAL/OGR with the Centroid function.