Hi John,
> How did you generate your projection coordinates and your lat/lon coordinates?
This is extracted code, but it demonstrates how we calculate our projection coordinates:
double cellSizeX=3.0004032;
double cellSizeY=-3.0004032;
double offsetX=-1856;
double offsetY=-1856;
size_t dimXLen=3712;
size_t dimYLen=3712;
for(size_t j=0;j<dimXLen;j++){
double x=(offsetX+double(j))*cellSizeX+cellSizeX/2;
((double*)varX->data)[j]=x;
}
for(size_t j=0;j<dimYLen;j++){
double y=(offsetY+float(j))*cellSizeY+cellSizeY/2;
((double*)varY->data)[j]=y;
}
We calculate the lat/lon coordinates usually with the proj4 library using the following string:
"+proj=geos +lon_0=0.000000 +lat_0=0 +h=35807.414063 +a=6378.169 +b=6356.5838"
But in case of MSGCPP these fields are already present in the source files we create our data from.
Regards,
Maarten
On 01/25/2012 01:05 AM, John Caron wrote:
> On 1/24/2012 3:12 AM, plieger wrote:
>> Hi John and Martin,
>>
>> John: Thanks a lot for the information. I put the MSGnavigation properties in the file, and the
>> projection now fits much better than the vertical perspective projection. Attached you will see a
>> screenshot of the longitude variable with this projection. At the edges of the globe I still see a
>> small offset of 0-0.1 degrees, but this is changing more or less where you query.
>> I tinkered a little bit with the height_from_earth_center and the semi_major and semi_minor axis,
>> but did not result in a noticable change of the projection. The 2D latitude and longitude fields are
>> always provided with these files so the projection can be verified with these fields.
>>
>>> char projection
>>> projection:proj4_params = "+proj=geos +lon_0=0.000000 +lat_0=0 +h=35807.414063 +a=6378.169
>>> +b=6356.5838" ;
>>> projection:grid_mapping_name = "MSGnavigation" ;
>>> projection:longitude_of_projection_origin = 0.f ;
>>> projection:latitude_of_projection_origin = 0.f ;
>>> projection:semi_major_axis = 6356584.f ;
>>> projection:semi_minor_axis = 6378169.f ;
>>> projection:height_from_earth_center = 4.216397e+07f ;
>>> projection:scale_x = 35785.83f ;
>>> projection:scale_y = -35785.83f ;
>>
>
> Hi Maarten:
>
> Yes, it seems as good as Ive seen.
>
> How did you generate your projection coordinates and your lat/lon coordinates?
>
> John
>
>
>
>
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>
--
Maarten Plieger
KNMI, R&D Information and Observation Technology, De Bilt
(t) +31 30 2206330
Received on Wed Feb 01 2012 - 08:39:51 GMT
