[Proj] PROJ.4: pj_transform parameters

Mikael Rittri Mikael.Rittri at carmenta.com
Thu Oct 4 12:50:22 EST 2012

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.


Mikael Rittri

4 okt 2012 kl. 19:07 skrev "Doanh Hoang" <doanh.hoang at mud-maps.com<mailto: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. "


On 4 October 2012 23:48, nicolas david <<mailto:ericnico.david at gmail.com>ericnico.david at gmail.com<mailto:ericnico.david at gmail.com>> wrote:

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.


2012/10/4 Doanh Hoang <<mailto:doanh.hoang at mud-maps.com>doanh.hoang at mud-maps.com<mailto: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;
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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