Here's a version I wrote. Needs a bit of tidying up but at least it works for any camera position and angle.
sync on : sync rate 0 : autocam off
mat_x#=500 : mat_y#=2000 : mat_z#=200
mat_size_x=1000 : mat_size_z=1000
mat_tiles_x=32 : mat_tiles_z=32
make matrix 1,mat_size_x,mat_size_z,mat_tiles_x,mat_tiles_z
position matrix 1,mat_x#,mat_y#,mat_z#
randomize matrix 1,10
update matrix 1
position camera mat_x#-50,mat_y#+100,mat_z#-50
point camera mat_x#+50,mat_y#,mat_z#+50
do
gosub mousetile
if tx > -1
text 0,0,"X = "+str$(tx)+", Z = "+str$(tz)
endif
sync
loop
mousetile:
tx=-1 : ty=-1 : t=0
for f=0 to 5000 step 100
pick screen mousex(),mousey(),f
x#=get pick vector x()+camera position x() : y#=get pick vector y()+camera position y() : z#=get pick vector z()+camera position z()
if x# > mat_x# and x# < (mat_size_x + mat_x#) and z# > mat_z# and z# < (mat_size_z + mat_z#)
h#=get ground height(1,x#-mat_x#,z#-mat_z#) : v#=y#-h#-mat_y# : if v# < 0 then t=1 : exit
endif
next f
if t=1
t=0
for g=f-100 to f step 10
pick screen mousex(),mousey(),g
x#=get pick vector x()+camera position x() : y#=get pick vector y()+camera position y() : z#=get pick vector z()+camera position z() :
if x# > mat_x# and x# < (mat_size_x + mat_x#) and z# > mat_z# and z# < (mat_size_z + mat_z#)
h#=get ground height(1,x#-mat_x#,z#-mat_z#) : v#=y#-h#-mat_y# : if v# < 0 then t=1 : exit
endif
next g
if t=1
t=0
for h=g to g-10 step -1
pick screen mousex(),mousey(),h
x#=get pick vector x()+camera position x() : y#=get pick vector y()+camera position y() : z#=get pick vector z()+camera position z() :
if x# > mat_x# and x# < (mat_size_x + mat_x#) and z# > mat_z# and z# < (mat_size_z + mat_z#)
h#=get ground height(1,x#-mat_x#,z#-mat_z#) : v#=y#-h#-mat_y# : if v# >= 0 then t=1 : exit
endif
next h
if t=1
tx=int((x#-mat_x#)/(mat_size_x/mat_tiles_x))
tz=int((z#-mat_z#)/(mat_size_z/mat_tiles_z))
endif
endif
endif
return
Boo!
