[PROJ] Make push and pop FIFO?

[Thomas Knudsen]

Hi Jochem,

So if I'm not entirely mistaken, you'll need something like the Forth "swap"
operator, or the PostScript "exch" operator to allow something like this:

###  The inverse part (read from bottom up, and read pop as push, push as
pop) ###

step omit_fwd proj=push v_3              # restore the geophysical height

# The bread and butter
step omit_fwd proj=tmerc inv lat_0=12.180658675 lon_0=-68.251802281 k_0=1
x_0=23209.5600 y_0=21423.9900 ellps=intl
step omit_fwd proj=cart ellps=intl
step omit_fwd proj=helmert x=-366.1939 y=-115.0688 z=-776.7039 rx=20.963080
ry=16.462749 rz=-14.276379 s=-12.80900 convention=coordinate_frame exact
step omit_fwd proj=cart inv ellps=GRS80

# The great swap show...
step omit_fwd proj=push v_3              # restore the geometrical height
step omit_fwd proj=exch                  # swap the two heights, to get the
geometrical to the top-of-stack
step omit_fwd proj=pop v_3               # save the geophysical height
step omit_fwd proj=vgridshift grids=egm2008_0_45.tif inv
step omit_fwd proj=pop v_3                 # save the geometrical height
# End of inverse part - read from here and upwards

In that case, I think the start of a solution would be to open an issue
over at https://github.com/OSGeo/PROJ/issues, requesting an
exch/swap operator, and summarizing this thread
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