[mapserver-users] Calculate Bounding Box...

[Julien-Samuel Lacroix]

Hi,

Probably not totally exact, but enough for most people:

Miles per degree (latitude):  69
Miles per degree (Longitude): 69 * (cos(LATITUDE * PI / 180))

Julien

PS: Set of PHP functions from Chameleon
http://chameleon.maptools.org/

/**
  * Number of KM in a MILE
  * there are 5280 feet in a mile        : start with 5280
  * there are 12 inches in a foot        : multiple by 12
  * there are 0.0254 meters in an inch   : multiple by 0.0254
  * there are 1000 meters in a kilometer : divide by 1000
  */
define( "KM_PER_MILE", (5280 * 12 * 0.0254 / 1000) );

/**
  * Constant returns miles per degree of latitude which is 69.
  */
define( "MilesPerDegreeLat", 69 );
define( "DegreesLatPerMile", (1 / 69.0) );


/**
  * function LonToLatRatio
  *
  * Given a latitude in decimal degrees, it will return the ratio of
  * longitude degress to latitude degrees.
  */
function LonToLatRatio ($latitude)
{
     return cos($latitude * M_PI / 180);
}

/**
  * MilesPerDegreeLon($latitude)
  *
  * Given a latitude in decimal degrees, it will return the
  * miles per degree of longitude.
  */
function MilesPerDegreeLon ($latitude)
{
     return 69 * LonToLatRatio($latitude);
}

/**
  * DegreesLonPerMile($latitude)
  *
  * Given a latitude in decimal degrees, it will return the
  * degrees of longitude per mile.
  */
function DegreesLonPerMile ($latitude)
{
     return 1 / MilesPerDegreeLon( $latitude );
}

Oscar Fdez. wrote:
> Thanks for your answer.
> 
> ¿Exist any formule to calculate the left/top lon/lan corner and the 
> right/bottom corner of Bounding Box dinamic from a lon/lan point?
> 
> Regards, Oscar.
> 
> 2009/3/12 Gregor at HostGIS <gregor at hostgis.com <mailto:gregor at hostgis.com>>
> 
>         I have a point in -8.0572,42.4702 (lon/lan). I like a bounding
>         box arround 1 mile of this site. Can use any SRS like EPSG:4230
>         or another.
> 
> 
>     Hit up spatialreference.org <http://spatialreference.org>
>     You can look up a SRS, then move a point over a map to get
>     conversions. Very handy.
> 
> 
> 
>     -- 
>     HostGIS, Open Source solutions for the global GIS community
>     Greg Allensworth - SysAdmin, Programmer, GIS Person, Security
>     Network+   Server+   A+   Security+
> 
> 
> 
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> 
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-- 
Julien-Samuel Lacroix
Mapgears
http://www.mapgears.com/