[Gvsig_english] Coordinate Transformations

[Victoria Agazzi]

Hi,
I know that DNRGarmin uses PROJ4 too, as the CRS manager of gvSIG do. I' 
m not a DNRGarmin's user, so I don't know if this extension is capable 
of transforming your CRS: I mean transforming from one datum to another.
With gvSIG you are able to project your geographic coordinates without 
changing your datum (this operation is called convertion) and on the 
other hand, you can transform the datum of your data (this operation is 
called transformation). You can also do a composed operation of both.

Regards,
Viqui-.

Antonio Gennarini escribió:
> Hi Victoria,
>
> many thanks for your very detailed reply. I have figured out that every
> transformation from 4326 to other projected coord systems will
> necessarily imply an error which is estimate in the 7-8m region. DO you
> think that programs such as DNRGarmin do worse that gvSIG, which I
> assume uses PROJ4 code?
>
> Cheers
> Antonio
>
>
> Il giorno lun, 11/08/2008 alle 10.29 +0200, Victoria Agazzi ha scritto:
>   
>> Hi Antonio,
>> if you are able to convert the *.gpx file to a *.shp file, then gvSIG 
>> transform the CRS from EPSG: 4326 to various OSGB reference systems:
>> 1. you will need to generate an shp file with your data (more than one 
>> if you have points, tracks, routes and texts). You can do this with [1]. 
>> These *.shp files will be in EPSG:4326.
>> 2. With gvSIG you need to create a new View in the CRS OSGB. To do this, 
>> create a new view, go to its Properties and select current projection. 
>> Search into the EPSG type, by name OSGB. Select one of them.
>> I searched into the CRS manager and found  6  CRS  that are OSGB: 4 that 
>> are geographic, 1 projected and another one compound.
>> 3. After that, you have to add your *.shp files which are in EPSG:4326. 
>> Open the View, Add data icon,  and select  the files.  For each one, you 
>> will have to change its CRS into 4326 (this is the way gvSIG "knows" in 
>> which CRS is your data). Click the current projection button, and look 
>> for the EPSG Type and 4326 code. Remember to define a transformation (in 
>> the Selec transformation list) between both CRS because they don`t have 
>> the same datum. You can select EPSG transformations, and also you can 
>> define a manual one if you know the parameters involved in your 
>> geographic area.
>> 4. At this point you will have your data in the OSGB projection but only 
>> in the actual view. Next step is to export the gvSIG layers into your 
>> hard disc. To do this, go to Layer/Export to/SHP.
>>
>> Regards,
>> Viqui-.
>>
>> [1] http://gpx2shp.sourceforge.jp/
>>
>>
>> Antonio Gennarini escribió:
>>     
>>> Hi.
>>>
>>> I'm in the process of learning howto deal with GPS data and have now the
>>> difficulty of transforming WGS84 coordinates in my *.gpx files to OSGB
>>> stored in a shapefile.
>>>
>>> ANybody now a relaxed way of doing this. I've been searching the web and
>>> have only found standalone applications that will allow me to convert
>>> the coordinates one by one and without reading directly from the gpx
>>> file.
>>>
>>>
>>> Thanks in advance for your help.
>>>
>>> REgards
>>> ANtonio
>>>
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