THEORY OF POLYCONIC PROJECTIONS. 37 



In figure 9 let The the pole, Q the center of the projection, 

 and let P be any given point. 



RGi 9. — Transformation triangle for stereographic horizon projection^ 



TP^l-<P 

 ZQTP=\ 



From the trigonometry of the spherical triangle we have 



cos p = sin a sin (p + cos a cos X cos (p 



sin V sin X . . . 



~= , or sm p cos co = sm X cos (p.. 



cos (p cosco' ^ ^ 



and 



sin p sin co = cos a sin (p — sin a cos X cos (p» 



