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Jochem,<span style="white-space: pre-wrap">
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cite="mid:AM0P192MB0482140E7871046743234EF7EF462@AM0P192MB0482.EURP192.PROD.OUTLOOK.COM">
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This new implementation uses a single stack instead of 4? So, the following pipeline would alter the ellipsoidal height and swap the original lon,lat? That is quite confusing for users that are used to the old push and pop.
+step +proj=stack +push=1,2 /
+step +proj=cart /
+step +proj=helmert +rx=1 +ry=2 +rz=3 /
+step +proj=cart +inv /
+step +proj=stack +pop=1,2</pre>
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<p>No, this wouldn't swap lon,lat. push=1,2 pushes the tuple (x,y)
to the top of the stack as (a=x,b=y) and pop=1,2 restores (a,b) as
(x,y). So this usage is strictly equivalent to using the old
operators with +proj=push +v_1 +v_2 and +proj=pop +v_1 +v_2.</p>
<p>Said otherwise "+proj=stack +push=1,2" is not equivalent to
"+proj=stack +push=1" followed by "+proj=stack +push=2".<br>
</p>
<p><br>
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cite="mid:AM0P192MB0482140E7871046743234EF7EF462@AM0P192MB0482.EURP192.PROD.OUTLOOK.COM">
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I am also wondering if the single stack could give new problems. How to access the stack values after the first two? This theoretical (but not unthinkable) case would still be impossible:
* input lon1 lat1 h1
* push lon1 lat1 h1
* helmert transformation to lon2 lat2 h2
* push lon2 lat2 h2
* pop lon1 lat1 h1
* helmert transformation to lon3 lat3 h3
* pop lon2 lat2
* output lon2 lat2 h3
</pre>
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<p>We'd probably need an extended stack swap operator, where you
could designate the indices of the stack that you want to exchange
(and you would need to push/pop separately (lon1, lat1) and (h1)).
But that becomes quite involved (for the user writing the
pipeline)<br>
</p>
<p>I guess you could probably also achieve that pipeline by
combining the "old" and "new" stacks (you can use both in the same
pipeline). But here, the solution for "normal" human brains
(assuming mine qualifies as normal) would probably be named
variables. There's some reason why Forth concepts haven't
percolated to more modern languages.<br>
</p>
<p>Even<br>
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<pre class="moz-signature" cols="72">--
<a class="moz-txt-link-freetext" href="http://www.spatialys.com">http://www.spatialys.com</a>
My software is free, but my time generally not.</pre>
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