[GRASS-user] Snap distance to clean imported map?

Rich Shepard rshepard at appl-ecosys.com
Wed Sep 11 17:24:34 PDT 2019

Importing a large (4.4G) vector map of wetlands takes a long time even on my
8-core/16-thread, 32G desktop. When it finally completed grass recommended
re-importing with an additional 'snap' distance specified:

Command line: > v.in.ogr in=OR_geodatabase_wetlands.gdb out=more_wetlands loc=geo_wetlands

WARNING: Number of incorrect boundaries: 88544
WARNING: The output contains topological errors:
          Unable to calculate a centroid for 329691 areas
          Number of incorrect boundaries: 88544
The input could be cleaned by snapping vertices to each other.
Estimated range of snapping threshold: [1e-09, 1]
Try to import again, snapping with 1e-05: 'snap=1e-05'

In the past 1e-05 produced similar warnings.

I'd like advice on two issues:

1) Is 1e-05 the most reasonable starting snap distance? (I assume it is a
generic value but perhaps not for all maps.) If not, what would be a snap
distance to use?

2) What would be a reasonable snap distance to stop re-importing when
warnings continue to be displayed?



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