[Proj] towgs params and epsg code for Italy regions

[massimo di stefano]

Hi All,

usually i need to reproject Italian data

from
Gauss Boaga rRome 40

to
Wgs 84

and inverse

when i need a good precision on a local scale extent, i use a set of  
control points (IGM95 vertex)
and apply last sqare methods to perform 2 different geometrics  
transformation :

1)  conforme transformation (4 parameters valid for only planimetry) ->

Tx (longitude - tanslation)
Ty (latitude - translation)
λ (scale factor)
α (rigid rotation)

2) affine transformation (6 parameters valid for only planimetry) ->

Tx (longitude - tanslation)
Ty (latitude - translation)
λx (longitude scale factor)
λy (latitude scale factor)
α (rigid rotation)
ϒ (angular sliding)


to transform vector files i apply the transformation parameters using  
pythn-gdal
but maybe (really i don't know) ...
it is possible to use these params directly in proj
(like we can do with cs2cs or including it inside an epsg code?)

....

an oher question :-/ ...

when i don't need more acuracy i use the follow +towgs params :

all the Italian region :

towgs84 = −225.000, −65.000, 9.000

Italian peninsular part :

towgs : −104.1, −49.1, −9.9, 0.971, −2.917, 0.714, −11.68

Sardinia :

towgs84 = −168.6, −34.0, 38.6, −0.374, −0.679, −1.379, −9.48

Sicily :

towgs84 = −50.2, −50.4, 84.8, −0.690, −2.012, 0.459, −28.08

i have taken the above params directly from grass gis and i include it  
in the epsg file that come with the proj source code.
Using it inside the epsg code 3004 - 3003 the errors is drastically  
reduced.

... my question :

instead of setting manually a customized projection,
is it possible to define new epsg code based on the +towgs paprameters  
inside the epsg file
and redistribuite it with the proj source code ?

.... a lot of software student and newbie gis users can beneficiate of  
it.

i agree i can manually add it to the epsg file, but mybe there is a  
reason beacouse these parameters are not already inside it ?
a license problem ?

Thanks to All for any answers,


Massimo Di Stefano
massimodisasha at yahoo.it

epifanio on   irc.freenode.net  /join gfoss









Massimo Di Stefano
massimodisasha at yahoo.it

epifanio on   irc.freenode.net  /join gfoss







-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.maptools.org/pipermail/proj/attachments/20090309/af0cfa1b/attachment.htm