Malformed building polygons


for some time now I wonder about malformed polygons rendered for buildings by mkgmap. It’s probably a misconfiguration on my side, but I can’t find a handle:

While using JOSM (or “official” OSM renderings) e.g. a church may have several small, more or less rectangular jutties, recesses and the like, its representation by

building='church' [0x0B level 2]

(from polygones) seems to render with missing (but also seemingly “new”) nodes, hence triangular shapes and overall malformed buildings, although the basic shape is there. To some degree this applies to many buildings having small displacements of sections. It even occurs if buildings are clustered (building at building, but with some parallel offset; the offset part renders malformed).

So far I could not identify the effect for other polygones, but it might be due to node density or proximity typically beeing higher for buildings.

Is there a parameter accessible I could tune to deal with that effect? (Toolchain: geofabrik downloads - osmconvert - splitter - mkgmap)



P.S.: Unfortunately I’m not able to attach screenshots or the like here, or how would I do that? I guess, the image tag accepts links only, does it?


Before posting I did comparisons to other peoples OSM based maps (~ identical toolchain), finding identical effects. But also vs. an old Topo D v6 Garmin .img, whose rendering / margin of error seems to be at least several times better. All the mentioned details that where deformed by mkgmap are rendered quite well, although some lines too seem not to be as parallel as by JOSM. (Would happily provide screenshots by pm…)

Nevertheless, I take it, that there is nothing I can do from my side.

Thanks Gerd

The newer Garmin NT format may allow higher precision, but mkgmap writes a format that already existed 20 years ago as we don’t know enough about the NT format. May change in the future.

Hello, did you manage to solve the problem? I have the same question.

Hi, I understood, its the old, low precision data format used by our maps that kinda “snaps” to a quite coarse grid. See Gerds replies. So, no solution here…
Cheers Felix

I haven’t checked, but mkgmap doesn’t support NT, does it?