clustering
I have profile data points which lie almost on a line (s. picture below)
Is there an easy way / plugin to add an attribute to each point which states to which profile line it belongs?
It should not be very difficult from a mathematical point of view in my opinion?
In other words: I want to create clusters from my points and each cluster should contain the points that belong to one profile line. So that in a second step I can fit a line through each of the profile points
If you can updgrade to postgis 2.2.0 you might be lucky because that feature has just been introduced. From the doc: "ST_ClusterWithin is an aggregate function that returns an array of GeometryCollections, where each GeometryCollection represents a set of geometries separated by no more than the specified distance."
Check this: http://postgis.net/docs/manual-2.2/ST_ClusterWithin.html
You want to look at Hierarchical Clustering to build your clusters. This will let you specify a cluster size based on your distance of interest (say, 1000m), rather than a number of clusters or a number of points within the cluster.
(Shameless plug) I've built a QGIS Processing plugin to implement clustering from the scipy library: Scipy Point Clustering. In this plugin is a tool for Hierarchical Clustering by Identifier where you can select a column in the point dataset to guarantee that only features with the same identifier will be clustered together. In your case you could use the species for example. It will then add a label field to the dataset with a cluster ID.
The plugin is marked as experimental, so you need to go to ‘Settings’ (once you've got to the Manage and Install Plugins windows) and check the box that has an option ‘Show also experimental plugins’, if that isn't already chosen.
I'd recommend playing with the linkage method when building the clusters. Most of the time either single or complete are the most useful I find;
single linkage says that points will be clustered together if a point is a maximum of the tolerance for any other point in the clustercomplete linkage requires that all points in the cluster are within the tolerance distance of each otherThere are details of the other parameters in the tool in the help, though I tend not to adjust those as much.
Best Answer
Ok, for now I found a solution:
Clustering points/polygons based on proximity (within specifed distance) using QGIS?
Its not based on statistics, but does what its supposed to!