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

Thu Jul 8 06:02:12 EDT 2010

  Ah, ok.

Hard to find all details by yourself. :)
Finds in the database, for example, that area 2847 is valid between Lat 
56 S, Lat 68 N, Lon 14 W and Lon 17 E approximately.

Just need to get it to a format my program like, XML will do fine and 
Excel should be able to do it.

Thanks
Tomas

Francis Markham skrev 2010-07-08 10:25:
> 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
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