Why there is a Tolerance parameter in oracle sdo_geom.sdo_length

Question

Documentation says that tolerance reflects the distance that two points can be apart and still be considered the same (for example, to accommodate rounding errors)

but in a length function there should be no number comparison.

Is it for the arc segments? or the geodetic coordinates?

Answer 1

Short answer: If the start and end nodes of a line are within the specified tolerance of each other, then the length of that line will be zero.

---

For background information on tolerance / rounding errors:

When the documentation mentions accommodating rounding errors, it's really talking about this type of scenario:

1 decimal degree / 60 = 0.01666666666 (recurring) decimal minutes

However, 0.01666666666 decimal minutes * 60 is not equal to 1 decimal degree, it's actually 0.9999999996.

Applying a tolerance of 0.1 (for example) to the comparison of these two values would treat the values as equal.

Answer 2

To clarify: the tolerance value is always expressed in meters for geodetic (long/lat) data. So a tolerance of 0.1 means 10cm.

For projected data, the tolerance is expressed in the unit for that projection - generally meters (but some US systems use feet).