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Add implementation considerations #7

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Add implementation considerations #7

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6 changes: 6 additions & 0 deletions README.md
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Expand Up @@ -12,6 +12,12 @@ Definitions of _z_, _x_, _y_ are the same as ones in the industry standard [Slip
# Characteristics
- Height of a voxel represented by a ZFXY with z=Z is 1 [m].

# Implementation considerations
- `log(tan( lat ) + (1 /cos( lat )))` can be more efficiently calculated as `log(tan( lat / 2 + 45 ))`.
- `(lng + 180) / 360` can be more efficiently calculated as `lng / 360 + 0.5`.
- Implementors may want to make use of `artanh(sin(lat))` where possible.
- We appreciate Mr. KAWASE Kazushige from Geospatial Informataion Authority of Japan for the proposals above.

# Future considerations
- More compact encodings of ZFXY may be considered in future.
- The value of `Z` is still subject to change.