Reports how many polygon vertices each region is drawn from. The total is
the figure the create_*() pipelines warn about when an atlas is large,
and the one atlas_simplify() brings down, so it is the number to watch
when tuning an atlas for size.
Value
A named integer vector, one element per geometry label value, in the
order those values appear in the atlas. When geometry is missing a label,
it is counted in a separate "<NA>" entry. Take sum() of the vector for
the atlas total; that total is every vertex the atlas carries, so it
always agrees with the large-atlas warning.
Details
Counts are summed across views, so a region that appears on the lateral and medial views is reported once.
See also
atlas_simplify() to bring the count down, and atlas_smooth(),
which raises it again – rounding a corner off means inserting points.
Other atlas geometry:
atlas_dilate(),
atlas_polish(),
atlas_simplify(),
atlas_smooth()
Examples
dk <- ggseg.formats::dk()
# The total is what the large-atlas warning reports.
sum(count_vertices(dk))
#> [1] 5391
# Which regions are the expensive ones?
head(sort(count_vertices(dk), decreasing = TRUE))
#> lh_superiortemporal rh_superiortemporal rh_postcentral rh_precentral
#> 178 158 154 154
#> lh_precentral lh_postcentral
#> 150 148