[PROJ] Help understanding grid files and +towgs84

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Hello, 

1) if you do not specify any datum you have so called "floating datum"
... meaning that it will be in what ever datum the library thinks is
most suitable for the situation. It will and should not assume any datum
if it is not given ... this is better behaviour (than assuming WGS84 as
it used to be, which created problems, jumps, and misunderstandings) 

2) see above (it used to be default ... but it was removed since it
created strange shifts (jumps)) -- for example large maps do not care
about datums since smallest details available (at one pixel scale) are
much larger than largest datum shifts anywhere used! 

Janne. 

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Nathan Woodrow kirjoitti 2019-01-22 00:59:

> Hi, 
> Now I'm just trying to understand mainly: 
> 
> 1) Why is +towgs84=0,0,0,0,0,0,0 needed on the target? As if it's not there it will just return the same values as the input 
> 2) Why is that not included as default?  
> 3) Is my understanding of the following correct?  Proj is really doing: GDA94 -> WGS84 -> Shifted WGS84 via grid -> GDA2020? 
> 
> Thanks, 
> Nathan
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