$LastChangedDate: 27-Juil-2011 $

# CL_gm_stationElevation

Elevation of any object as seen from ground stations.

## Calling Sequence

       [elev] = CL_gm_stationElevation(pos_ter,stations,[er,[obla]])

## Description

- Computes the elevations (elev) of any object as seen from one or several locations (stations).

  The position of the object (pos_ter) is given in cartesian coordinates in a frame tied to the planet (that is in the same frame as stations).

  See below for detailed examples

## Parameters

pos_ter:

  positions in the rotating frame, in cartesian coordinates [X;Y;Z] [m] (3xM)

stations:

  stations positions in the same rotating frame, in elliptical (geodetic) coordinates [long,lat,alt] [rad,m] (3xN)

er :

  (optional) planet equatorial radius (default is %CL_eqRad) [m] (1x1)

obla :

  (optional) planet oblateness (default is %CL_obla) (1x1)

elev:

  elevations from each stations and each object position. elev(row=i,column=j) is the elevation of object j from station i. [rad] (NxM)

## Authors

- CNES - DCT/SB

## See also

- CL_ev_visibility

## Examples

    //secular J2 propagation
    cjd0 = 21915;
    pas = 10./86400.0;
    cjd = cjd0 : pas : cjd0+1;
    kep0 = [7070.e3 ; 0.001 ; CL_deg2rad([98;90;10;15])];
    kep = CL_ex_secularJ2(cjd0, kep0, cjd);

    //conversion to terrestrial frame
    [pos_car,vel_car] = CL_oe_kep2car(kep);
    pos_ter = CL_fr_G502ter(cjd,pos_car);

    //stations definition
    sta1 = [CL_deg2rad(2);CL_deg2rad(70);200]; // high latitude
    sta2 = [CL_deg2rad(20);CL_deg2rad(0);400]; // equator
    stations = [sta1,sta2];

    //elevations computation
    [elev] = CL_gm_stationElevation(pos_ter,stations);

    // elevation in function of time
    scf();
    plot2d((cjd-cjd0)*24,CL_rad2deg(elev(1,:)),2) //station 1
    plot2d((cjd-cjd0)*24,CL_rad2deg(elev(2,:)),3) //station 2

    // visibility duration if station's mask is 5 degrees :
    ind_1 = find(elev(1,:) > CL_deg2rad(5));  //station 1
    ind_2 = find(elev(2,:) > CL_deg2rad(5));  //station 2
    dur_1_minutes = pas*length(ind_1)*1440.0
    dur_2_minutes = pas*length(ind_2)*1440.0