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

[Francis Markham]

Yeah, I mean the "area of use" as EPSG call it.  You can download the
EPSG database which contains a table with areas of use from
http://www.epsg.org/Geodetic.html and extract that for use in your
application if that is going to be helpful for you.

-F

On 8 July 2010 16:53, Tomas R <monshi at home.se> wrote:
>  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
>>>
>>> _______________________________________________
>>> gdal-dev mailing list
>>> gdal-dev at lists.osgeo.org
>>> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>>>
>
> _______________________________________________
> gdal-dev mailing list
> gdal-dev at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>