We investigate the geometry in a real Euclidean building
of
type
of some simple configurations in the associated projective plane at infinity
, seen as ideal
configurations in
,
and relate it with the projective invariants (from the cross ratio on
). In
particular we establish a geometric classification of generic triples of ideal chambers
of
and relate it with the triple ratio of triples of flags.
Keywords
Euclidean buildings, projective planes, ideal
configurations, triple ratio
