grade separation and shortest path on networks in spatstat

Question

I have a question not on spatstat but on use and limitation of spatsat.

During the calculation of metrics like pcf and k function equivalents on linear networks, a shortest path distance is used instead of euclidean distance. I have the spatsat book from 2015 and I remember reading somewhere in the text that the shortest path calculation on networks is not sensitive to grade separations like flyover, bridges, underpass and therefore caution should be exercised in selecting the study area or be aware of this limitation while interpreting results.

Is there any publication that discusses this limitation of grade separation in detail and may be suggesting some workarounds? Or limitations of network equivalents in general?

Thank you

Answer 1

The code for linear networks in spatstat can handle networks which contain flyovers, bridges, underpasses and so on.

Indeed the dataset dendrite, supplied with spatstat, includes some of these features.

The shortest-path calculation takes account of these features correctly.

The only challenge is that you can't build the network structure using the data conversion function as.linnet.psp, because it takes a list of line segments and tries to guess which segments are connected at a vertex. In this context it will guess wrongly.

The connectivity information has to be specified somehow! You can use the constructor function linnet to build the network object when you have this information. The connectivity can be edited interactively using clickjoin.

This is explained briefly on page 713 of the book (which also mentions dendrite).

The networks that can be handled by spatstat are slightly more general than the simple model described on page 711. Lines can cross over without intersecting.

I'm sorry the documentation is terse, but much of this information has been kept confidential until recently (while our PhD students were finishing).