pj_phi2(): speed-up computation (and thus inverse ellipsoidal Mercator and LCC) #2052
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mwtoews
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Mar 11, 2020
…r and LCC) This does not change the numeric values returned by the method, as far as I could see on a few samplings. The tricks used save a call to sin() and atan() at each iteration. This directly affects speed of inverse Mercator and LCC (among others), in their ellipsoidal formulation. Timings on inverse Mercator show a 31% speed-up at mid-latitudes where pj_phi2() needs 5 iterations, and 24% at latitudes close to 0 or 90deg where it needs one iteration.
rouault
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Mar 11, 2020
…ordinates with same northing Same rationale as in OSGeo#2043 When converting by batch of coordinates of 2000 consecutive same northings, the speed-up over master is 7 times for ellipsoidal formulation, and about 40% for the spherical formulation (and thus webmerc) On top of OSGeo#2052, the speed-up for ellipsoidal would also be about 40%
rouault
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to rouault/PROJ
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Mar 11, 2020
…ordinates with same northing Same rationale as in OSGeo#2043 When converting by batch of coordinates of 2000 consecutive same northings, the speed-up over master is 7 times for ellipsoidal formulation, and about 40% for the spherical formulation (and thus webmerc) On top of OSGeo#2052, the speed-up for ellipsoidal would also be about 40%
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This does not change the numeric values returned by the method,
as far as I could see on a few samplings.
The tricks used save a call to sin() and atan() at each iteration.
This directly affects speed of inverse Mercator and LCC (among others),
in their ellipsoidal formulation.
Timings on inverse Mercator show a 31% speed-up at mid-latitudes
where pj_phi2() needs 5 iterations, and 24% at latitudes close to 0 or
90deg where it needs one iteration.