[Proj] PROJ.4: pj_transform parameters

[Doanh Hoang]

Thanks Nicolas and Rittri for very good support .

I already understand more detail about transformation and input parameters
and the way to get them .

Thanks you very much !

Doanh

On 5 October 2012 00:50, Mikael Rittri <Mikael.Rittri at carmenta.com> wrote:

> I think you must add a final slash after 4326 to make that link work.
>
> Another site you could look at is <http://www.epsg-registry.org>
> http://www.epsg-registry.org
>
> The +init usually works, but when the underlying datum isn't
> WGS84, you will not always get the best possible accuracy.
> I believe the default implementation of OSGB36 isn't
> very good, for example (it may have improved since
> the last time I looked, though).
>
> For ED50, I don't know any implementation that is good in
> all of Europe/Middle East. The default has about 10 - 15 m
> accuracy. If one needs higher accuracy, one must
> choose an implementation that is tailor-made for a
> smaller area, say Spain or some part of the North Sea.
>
> Regards,
>
> Mikael Rittri
> Carmenta
> Sweden
> http://www.carmenta.com
>
> 4 okt 2012 kl. 19:07 skrev "Doanh Hoang" <doanh.hoang at mud-maps.com>:
>
> Hi David.
>
> Thank you for quick support !
>
> Is it right that for another datums (for example : NAD27, NAD83, OSGB, ED
> 50, etc,...) we can do transformation with only just simple initialization
> like projPJ src= pj_init_plus( "+init=epsg:4326"); (I mean that we use
> only +init parameter)
>
> Clicking on <http://spatialreference.org/ref/epsg/4326>
> http://spatialreference.org/ref/epsg/4326 I get :  " Not found,
> /ref/epsg/4326. "
>
> Doanh
>
> On 4 October 2012 23:48, nicolas david < <ericnico.david at gmail.com>
> ericnico.david at gmail.com> wrote:
>
>> Hi
>>
>> On our proj4 installation you should have a directory call "nad". This
>> directory have some dictionnary of projection that could be used to define
>> projection parameters. For exemple with the lat/long wgs84 projection you
>> could use
>>
>> projPJ src= pj_init_plus( "+init=epsg:4326");
>>
>> see <http://spatialreference.org/ref/epsg/4326>
>> http://spatialreference.org/ref/epsg/4326 for searching your projection
>> code.
>> Take care of setting the PROJ_LIB environnement variable to the correct
>> path for your projection directory.
>>
>> Nicolas
>>
>>
>> 2012/10/4 Doanh Hoang < <doanh.hoang at mud-maps.com>
>> doanh.hoang at mud-maps.com>
>>
>>>  Hi all
>>>
>>> Im developer and this is the first time I touch PROJ.4 . And I have
>>> following problem , please anyone can give me an advice:
>>>
>>> In my project I need to do *transformation from datums  (US, North
>>> America, UK, South Africa, New Zealand) to WGS84. *
>>>
>>> After having a look at defintion of pj_transform  (function to do datums
>>> transformation on PROJ.4). I have seen that there are so many input
>>> parameters.
>>>
>>> For example : following code that I found in internet :
>>>
>>> ------------------------------------------------------------------------------------------------------
>>>     projPJ src= pj_init_plus("+proj=tmerc +lat_0=38N +lon_0=128E
>>> +ellps=bessel +x_0=400000 +y_0=600000 +k=0.9999
>>> +towgs84=-146.43,507.89,681.46");
>>>     projPJ dst= pj_init_plus("+proj=latlong +datum=WGS84 +ellps=WGS84");
>>>     double x,y,z;
>>>     x=100;
>>>     y=100;
>>>     z=100;
>>>     pj_transform(src,dst,1,1,&x,&y,NULL);
>>>
>>> ------------------------------------------------------------------------------------------------------
>>>   params for initionlization of datums
>>> +proj=merc +ellps=clrk66 +lat_ts=33  +proj=latlong +ellps=clrk66 ------------------------------------------------------------------------------------------------------
>>> There are so many geospatial knowledge neccessary to understand these
>>> parameter.
>>> Im developer and I know just only the simple name of datums(WGS84,
>>> NAD27, NAD83, etc,..) and coordinates of points,
>>>
>>> With them how I can make transformation between different datums ? *Where
>>> I can get input parameters and define correct geospatial input parameters.
>>> *
>>>
>>> I very need your help. Thanks a lot.
>>>
>>> Hoang Doanh
>>>
>>>
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