With any flock F of the quadratic cone K of PG(3, q) there corresponds a generalized quadrangle S(F) of order (q(2),q) For q odd Knarr gave a pure geometrical construction of S(F) starting from F Recently, Thas found a geometrical construction of S(F) which works for any q. Here we show how, for q odd, one can derive Knarr's construction from Thas' one. To that end we describe an interesting representation of the point-plane flags of PG(3, q), which can be generalized to any dimension and which can be useful for other purposes. Applying this representation onto Thas' model of S(F), another interesting model of S(F) on a hyperbolic cone in PG(6,q) is obtained. In a final section we show how sub-quadrangles and ovoids of S(F) can be obtained via the description in PG(6, q) (C) 2001 Academic Press. [References: 19]
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