[GRASS-dev] Location wizard (missed window to select +towgs params)

[Paul Kelly]

On Fri, 12 Mar 2010, Markus Neteler wrote:

> On Fri, Mar 12, 2010 at 8:38 PM, Martin Landa <landa.martin at gmail.com> wrote:
>> Hi,
>>
>> 2010/3/12 Massimo Di Stefano <massimodisasha at gmail.com>:
>>>  "location wizard -> select epsg code -> search for : 3004"
>>>
>>> in the paste release (build less than 1 month ago) after select the epsg:code(3004)
>>> grass prompt me to the window :
>>>
>>> http://img534.imageshack.us/img534/8254/schermata20100312a09564.png
>>>
>>> to select the +towgs parameters
>>>
>>> with the latest svn version this window doesn't appair and  the locaqtion is created using the defaults parameters :
> ...
>> it seems to be bug in g.proj -
>>
>> g.proj epsg=3004 datum=-1
>>
>> no output is printed...
>
> When you add -t, it works:
>
> g.proj epsg=3004 datum=-1 -t

The fact that the -t flag needs to be specified, suggests that somehow 
when g.proj is querying GDAL for a projection description for EPSG code 
3004, it is coming back fully specified, i.e. with complete towgs84 
parameters, and thus g.proj thinks the datum information is already all 
specified and correct, so it doesn't even offer the option of modifying it 
unless the user requests to override the datum information in the input 
co-ordinate system with the -t flag. (I'm sure there is a logical reason 
for working like that although it doesn't immediately come to mind at the 
minute!)

I'm not very sure what's going on though. I will look into it, although it 
might be 2-3 days before I have an answer.

Paul