CL_gm_pixelSize

Description

• Computes the size factors of the footprint of a conic sensor at an angle to the descending vertical.

  If the footprint is small enough, it can be considered as the intersection between a cone of revolution and the plane tangent to the planet surface (and containing the target location).

  Then:

  - The footprint outline is a circle with radius D when the sensor is looking to the descending vertical.

  - It is an ellipse with semi-major axis f1*D and semi-minor axis f2*D when the sensor is tilted at an angle (tilt) to the vertical.

  Two effects are responsible for the change of size: increase of distance (reflected in f1 and f2) and increase of incidence angle (reflected in f1 only).

  

• Note:

  - A spherical planet is assumed.

Parameters

sat_alt:

Satellite altitude [m] (1xN)

tilt:

Angle to the descending vertical [rad] (1xN)

target_alt:

(optional) Target altitude [m] (default is 0)(1xN)

er :

(optional) Planet radius (default is %CL_eqRad) [m]

f1:

Size factor in tilt plane(1xN)

f2:

Size factor in direction perpendicular to tilt plane(1xN)

Authors

• CNES - DCT/SB

See also

• CL_gm_visiParams

Examples

// Example 1 sat_alt = 700.e3; tilt = CL_deg2rad(20); [f1,f2] = CL_gm_pixelSize(sat_alt,tilt) // Same computation, with CL_gm_visiParams : eqRad = CL_dataGet("eqRad"); sat_radius = eqRad + sat_alt; target_radius = eqRad; // distance for the given tilt [dist] = CL_gm_visiParams(sat_radius,target_radius,'sat',tilt,'dist') // elevation for the given tilt [elev] = CL_gm_visiParams(sat_radius,target_radius,'sat',tilt,'elev') f1 = dist/(sat_alt * sin(elev)) f2 = dist/sat_alt