[Proj4j] ESPG:28992

[Martin Davis]

On a more general note, this discussion points to the need for more unit 
tests in Proj4J!  A wider set of unit tests would surely have caught the 
issue with the missing conversion of the datum transform parameters.

When the dust has settled over this I'll work on adding a unit test 
based on this data.

On 1/11/2012 3:03 PM, Gertjan Idema wrote:
> Hi Fitz,
>
> I just wrote a test script and can confirm your result.
> Then I remembered that there was a difference between proj (c-version) 
> and proj4j in handling the +towgs parameters.
> The c version has some conversion code for parameters 4-7.
> Parameters 4-6 get converted from arc seconds to radians. 
> (param=param*pi/180/3600)
> Parameter 7 gets converted from ppm to scaling factor 
> (param=1+param/1000000)
>
> Here's the code from pj_datum_set.c:
>   /* transform from arc seconds to radians */
>   projdef->datum_params[3] *= SEC_TO_RAD;
>   projdef->datum_params[4] *= SEC_TO_RAD;
>   projdef->datum_params[5] *= SEC_TO_RAD;
>   /* transform from parts per million to scaling factor */
>   projdef->datum_params[6] =  (projdef->datum_params[6]/1000000.0) + 1;
>
> This code seems to be missing in proj4j.
>
> Apart from that, as far as I know, the +towgs should be 
> :+towgs84=565.237,50.0087,465.658,-0.406857,0.350733,-1.87035,4.0812
> Applying the above calculation to the last 4 parameters as a work 
> around gives:
>   
> +towgs84=565.237,50.0087,465.658,-1.972e-6,1.7004e-6,-9.0677e-6,1.0000040812
>
> When I put this into the nad/epsg file for proj4j I thought I would 
> get the same results you got from proj, but I didn't.
> I get 155029.79163595638 463109.9538034333 for your reference point 
> instead.
>
> However, the result seems to agree with some other data I have. I'll 
> do some more research tomorrow.
>
>
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