# Map Projection Info Map Projection Type = Lambert Conformal

## Description

A conformal, conic projection where the parallels are unequally spaced arcs of
concentric circles, more closely spaced near the center of the map. Meridians
are equally spaced radii of the same circles, thereby cutting parallels at right
angles. Scale is true along the standard parallel(s). The pole in the same
hemisphere as standard parallel(s) is a point, while the other pole is at
infinity (See Snyder 1987, Ch 15. Lambert Conformal Conic Projection,
pp 104-110).                                          
                                                                        
In general the transformation from the cartographic coordinates X, Y to line and
sample in the PDS image is as follows:                 
                                                                        
sample = INT( X + SAMPLE_PROJECTION_OFFSET) +1                          
line   = INT(-Y + LINE_PROJECTION_OFFSET) +1                            
                                                                        
where                                                                   
      X = F1(latitude,longitude)                                        
      Y = F2(latitude,longitude)                                        
                                                                        
                                                                        
and F1(latitude,longitude) and F2(latitude,longitude) are the cartographic
formulas described detailed in (Snyder 1987)               
                                                                        
                                                                        
Equations (14-1), (14-2), (15-1), (14-4), (15-1a), (15-2), (15-3), (15-5), (14-9)
(14-10) and (14-11), of USGS Paper 1395 (pp 106,107) were used.           
                                                                        
Batson et al, 1992 suggest quadrangle schemes that apply a secant cylinder
Mercator projection for the equatorial to low latitude areas. As this projection
is seldomly implemented in common image data and analysis software, the LAMBERT
CONFORMAL projection is used as a substitute. The absolute values of the two
standard parallels are set to differ by 0.001 degrees to approximate the secant
cylinder Mercator projection.                                           
                                                                        
The majority of the map projection descriptions in this document follow the
descriptions in Snyder (1987) closely. Used keywords and values with respect to
map projections follow the PDS3 standard reference whereas a detailed description
of the parameter's scope and definition can be found in the PDS dictionary.
LINE_PROJECTION_OFFSET/SAMPLE_PROJECTION_OFFSET are the line/sample values minus
one onto which the map projection origin falls.

## References

Acton, Jr. C.H., Ancillary Data         
     Services of NASA's Navigation and Ancillary Information Facility,
     Planetary and Space Sciences, 44, Number 1, pp. 65-70, 1996.

Greeley, R. and Batson, G., 1990, Planetary Mapping,             
     Cambridge University Press.

Planetary Science Data Dictionary Document,
    Document JPL D-7116, Rev. F, October 20, 2008

Snyder, J.P., 1987, Map Projections - A Working Manual,          
     US Government Printing Office, Washington, p. 42.

Snyder, John P., Map Projections - A Working Manual,
U. S. Geological Survey  Professional Paper 1395, 383p., 1987.