Description
The Database Deviation and Relative Database Deviation examine metrics are available
when at least one domain is selected for Examine. These metrics are intended to estimate the
deviation between the linear cell and the curved high-order (H-O) cell projected onto the underlying
database.
Tip: Database Deviation and Relative Database Deviation
are computed using the stencil for a 4th order (Q4) surface cell. This provides a reasonable
estimate of the deviation observed during
H-O elevation. Minimizing deviation
typically results in less required curving and smoothing during the H-O export process.
Database Deviation is computed by sampling the cell using the 4th order stencil
(shown in the images below) and projecting the H-O nodes onto the underlying database.
The final Database Deviation is then calculated by taking the maximum projection distance
(or deviation) of all the H-O nodes.
Relative Database Deviation is computed in the same way, except that it scaled by the
maximum edge length of the linear cell:
Ddatabase = max [di]
Drelative = max [di] / max [Lj]
where:
di = the deviation between the linear and projected position at H-O
node i
lj = the length of cell edge j
Note: Domains that are not database constrained (i.e. free) have a
Database Deviation and Relative Database Deviation of 0.
The value of Database Deviation and Relative Database Deviation varies from 0
(good) to ∞ (bad). Large values indicate
that the linear mesh may need additional refinement to adequately resolve the underlying
database
curvature during
H-O elevation. Domains that are not database constrained
(i.e. free) have a deviation of 0.
The probe renders the 4th order stencil for triangles (left) and quadrilaterals (right) with
additional line segments denoting the displacement from the linear cell for each H-O node.
For these functions, the probe renders both the linear and projected H-O node locations for
the 4th order cell. Although only the maximum distance is reported for these metrics, you can use the
Point Probe functionality to measure the
displacement for any of the H-O points rendered.
Tip: When examining Database Deviation and Relative
Database Deviation, use the probe
functionality to visualize the curved 4th order surface cell (triangle or quadrilateral) and the
point probe functionality to measure the
displacements of the H-O nodes. This gives you a good idea of how much curving will be
required during H-O export.