[gdal-dev] Re: C#: Retrieve boundary of coordinate system

[Tomas R]

  You mean
  area_of_use_code="2847"
which gives
<Area area_code="2847" area_name="Sweden - 2.5 gon W" 
area_of_use="Sweden. For medium and small scale applications:- all 
country. For large scale applications:- communes between approximately 
14 deg 40 min and 16 deg 55 min East. See information source for map." 
information_source="Lantmateriverket (National Land Survey of Sweden). 
http://www.lm.se/geodesi/refsys/rt/rt_projections.html" 
data_source="EPSG" revision_date="2003-06-27" deprecated="0"/>


Or is it from this line
<3021> +proj=tmerc +lat_0=0 +lon_0=15.80827777777778 +k=1.000000 
+x_0=1500000 +y_0=0 +ellps=bessel +units=m +no_defs <>

or from the WKT
PROJCS["RT90 2.5 gon 
V",GEOGCS["RT90",DATUM["Rikets_koordinatsystem_1990",SPHEROID["Bessel 
1841",6377397.155,299.1528128,AUTHORITY["EPSG","7004"]],TOWGS84[414.1055246174,41.3265500042,603.0582474221,-0.8551163377,2.1413174055,-7.0227298286,0],AUTHORITY["EPSG","6124"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.01745329251994328,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4124"]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",15.80827777777778],PARAMETER["scale_factor",1],PARAMETER["false_easting",1500000],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AUTHORITY["EPSG","3021"]]

or some other file/source?
All data regarding the Swedish RT90 2.5 V  where only the WKT is 
complete with toWGS84 parameters.
A not so easy task, and not reliable, to retrieve the info from there I 
would guess.

My goal is not to be 100% accurate at all points in the world, my goal 
is to be consistent in the answers to the calls I get. That is the 
functions PixelToGPS and GPSToPixel should return "compatible" results 
at all parts in the world so that the main application won't have any 
risk of getting confused and run into infinite loops or alike.
not to hard to step from (in WGS84) 180 to -180 and +85 to -85 and check 
for every  fifth degree, or so, if the transformation is valid.  When 
transformation not valid the plan is to switch to WGS84 which seems to 
work even though results can be interesting in the boundary between the 
coordinate systems.

But still, if the info already exists somewhere why not use it but I do 
not know if that info exist in the data I have available.

Thanks anyway
Tomas

Francis Markham skrev 2010-07-08 08:14:
> I think the EPSG dictionary defines areas of validity for the defined
> coordinate systems.  That could be a starting point, although there
> may be a better solution
>
> -Francis
>
> On 8 July 2010 16:01, Tomas R<monshi at home.se>  wrote:
>>   No one?
>>
>> Ok, I guess then that there are no common function/method of doing this. My
>> approach will the be trial and error. From WGS 84 transform to the local
>> coordinate system and back again to WGS84 and check if the result seems
>> valid.
>>
>> Should work or any expert here have another solution?
>>
>> Yours
>> Tomas
>>
>> Tomas R skrev 2010-07-05 09:05:
>>>   Attacking GDAL via the C# interface and I have a question
>>>
>>> Have set up two (Osr) SpatialReferences  and transformations to and form
>>> both. One system is WGS84 and the other is unknown.
>>>
>>> To get a consistent behaviour I need to retrieve the boundary, in WGS84
>>> coordinates, of the unknown system. If known I can fallback on WGS84 when
>>> calls outside the scope of the coordinates system are made.
>>>   Should be easy to read of some attribute of the SpatialReference or
>>> alike. But which/how?
>>>
>>> Any suggestions?
>>>
>>> Or how should I solve it - in general words:
>>> My application maps coordinates from and to WGS84 and serves them to
>>> another via calls like PixelToGPS and GPSToPixel. The originating coordinate
>>> system is always WGS84. Need to handle calls made outside the scope of the
>>> coordinate system and my approach, to get a consisting behaviour of the two
>>> functions, is to revert to WGS84 which is defined at all possible points.
>>>
>>>
>>> Yours
>>> Tomas
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