Generalization: discrete isolation: meaning of column values

[hiddewie]

Hello,

I am playing around with the experimental discrete isolation features of Osm2pgsql. Following the documentation in https://osm2pgsql.org/doc/manual.html#strategy-discrete-isolation and the blogpost https://blog.jochentopf.com/2022-12-19-selecting-settlements-to-display.html.

The goal is similar to the blog post, to improve the rendering of worldwide train stations on the map, using a calculated measure of importance stored in a database column. Some work in progress is in hiddewie/OpenRailwayMap-vector#633.

In the original blog post is the sentence

For the map above I used the formula "discr_iso_rank < (3.5 ^ @zoom_level) * 10 and importance_rank < (10 ^ @zoom_level)" to decide which places to show and which not to show. Of course, that’s only an example and it has to be tuned for different types of maps etc.

I would like to understand the exact meaning of the three columns discr_iso, irank and dirank better, in order to tune the values in the SQL queries. Can you elaborate on the exact meaning of the columns, the (expected) value ranges, and what high and low values mean, and how to interpret the values in the columns together?

Thanks in advance.

[joto]

I have extended the manual to contain some more information. Hope this helps.

[hiddewie]

Thanks, this helps. One question.

In the manual, the discrete isolation value is documented as

Discrete isolation value. This is the smallest distance from this feature to all other features on the map in map units.

The linked paper lists in section "3.3 Discrete Isolation"

The Discrete Isolation is the point’s distance to the closest point with a higher value, as Fig. 7 shows

So which is it: the smallest distance to all other features on the map, or the smallest distance to another feature with a higher importance value?

[joto]

The description from the paper is correct. I have updated the manual.