Projection definitions for epsg:2391-2393 (Finnish KKJ)

[Külli Tiits]

Frank Warmerdam wrote:

> Rahkonen Jukka wrote:
> 
>> Hello,
>>
>> For some reasons there are two versions of Finnish KKJ parameters hanging
>> around in the projection libraries.  I checked that the situation is the
>> same at least in MS4W and FW Tools Windows packages.  In the files
>> "\FWTools1.2.2\proj_lib\epsg" and "\ms4w\proj\nad\epsg" the definition 
>> are
>> like this: <2393> +proj=tmerc +lat_0=0 +lon_0=27 +k=1.000000 +x_0=3500000
>> +y_0=0 +ellps=intl +units=m +no_defs  <>
> 
> ...
> 
>> I think that the definitions in epsg file should be corrected. Or is 
>> there
>> some reason, historical or other, for not including the towgs84 
>> parameters
>> there?
> 
> 
> Jukka,
> 
> The epsg file is generated from the EPSG database and only includes towgs84
> parameters for geographic coordinate systems that have one, and only one,
> transformation from that GCS to WGS84 using 3 or 7 parameter 
> transformations.
> 
> If there are multiple ways (multiple sets of parameters) then to be "safe"
> none of them are used.
> 
> I don't know if that is the case in for KKJ or not without quite a bit of
> digging.

I looked the EPSG database now. And yes, it is the case. There are two 
sets of parameters available, both 7 parameter. The old (or currently 
used in the esri:239x) parameters have also the comment that they have 
been superseded with the new version 2. The ver2 parameteres are almost 
the same as in the *official* Finnish standard, they have just less 
digits after comma..

I do not know, how the ESRI coordinate system list is generated, but in 
newer ESRI software also both of these transformations are available.

So in my opinion the correct way would be to use the version 2 
parameters from the EPSG database.

Külli
> 
> If there was one clearly preferred set of parameters that you and everyone
> else can agree on, then I can set an override in the epsg file generation
> process to use that.  But I don't like to be in the position where I add
> them at one persons suggestion, and then someone else emails me suggesting
> different values.
> 
> Best regards,