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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">Hi Thomas,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">Thanks for your reply. I will open an issue, but I wanted to make sure I wasn’t overlooking an already available solution for my problem.
Also, I thought it might be better to find consensus in the email list first. Or would it be better to have a discussion like this in an issue? I am not so familiar with the do’s and don’ts of open-source collaboration.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><i><u><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">exch / swap<o:p></o:p></span></u></i></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">Your suggestion is a third way to solve my problem. That would work fine.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><i><u><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">LIFO / FIFO<o:p></o:p></span></u></i></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">Switching from LIFI to FIFO seems an easier solution to me. But I have no experience with stacks in programming languages, so maybe
FIFO is too unconventional? Or would the change in behaviour from LIFI to FIFO be problematic for other users? I have never seen a PROJ pipeline using more than one value on the stack.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><i><u><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">Alternative<o:p></o:p></span></u></i></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">A difference between PROJ and the language Forth is that PROJ has a coordinate value next to the stack. My suggested
</span><span lang="EN-GB" style="font-size:11.0pt;font-family:Consolas;mso-fareast-language:EN-US">flip</span><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"> operator does the same as your
</span><span lang="EN-GB" style="font-size:11.0pt;font-family:Consolas;mso-fareast-language:EN-US">exch</span><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"> /
</span><span lang="EN-GB" style="font-size:11.0pt;font-family:Consolas;mso-fareast-language:EN-US">swap</span><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"> operator. The only difference is that I interpret
the current coordinate value as the top value of the stack. The advantage is that my alternative needs just one step:
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:35.4pt"><span lang="EN-GB" style="font-size:11.0pt;font-family:Consolas;mso-fareast-language:EN-US">+step +proj=flip +v_3<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">to do the same are your 3 steps:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:35.4pt"><span lang="EN-GB" style="font-size:11.0pt;font-family:Consolas;mso-fareast-language:EN-US">step omit_fwd proj=push v_3
</span><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"># restore the geometrical height</span><span lang="EN-GB" style="font-size:11.0pt;font-family:Consolas;mso-fareast-language:EN-US"><o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:35.4pt"><span lang="EN-GB" style="font-size:11.0pt;font-family:Consolas;mso-fareast-language:EN-US">step omit_fwd proj=exch
</span><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"># swap the two heights, to get the geometrical to the top-of-stack<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:35.4pt"><span lang="EN-GB" style="font-size:11.0pt;font-family:Consolas;mso-fareast-language:EN-US">step omit_fwd proj=pop v_3
</span><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"># save the geophysical height</span><span lang="EN-GB" style="font-size:11.0pt;font-family:Consolas;mso-fareast-language:EN-US"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><i><u><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">Name<o:p></o:p></span></u></i></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">Even if my alternative behaviour of
</span><span lang="EN-GB" style="font-size:11.0pt;font-family:Consolas;mso-fareast-language:EN-US">flip</span><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"> would be implemented, I think your suggested
name </span><span lang="EN-GB" style="font-size:11.0pt;font-family:Consolas;mso-fareast-language:EN-US">exch</span><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"> or
</span><span lang="EN-GB" style="font-size:11.0pt;font-family:Consolas;mso-fareast-language:EN-US">swap</span><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"> would better explain what it does. Could there
be a need for other stack operators too, like </span><span lang="EN-GB" style="font-size:11.0pt;font-family:Consolas;mso-fareast-language:EN-US">dup</span><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">,
</span><span lang="EN-GB" style="font-size:11.0pt;font-family:Consolas;mso-fareast-language:EN-US">over</span><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">,
</span><span lang="EN-GB" style="font-size:11.0pt;font-family:Consolas;mso-fareast-language:EN-US">rot</span><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"> and
</span><span lang="EN-GB" style="font-size:11.0pt;font-family:Consolas;mso-fareast-language:EN-US">drop</span><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">? To avoid confusion with other PROJ operators
like </span><span lang="EN-GB" style="font-size:11.0pt;font-family:Consolas;mso-fareast-language:EN-US">axisswap</span><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"> and
</span><span lang="EN-GB" style="font-size:11.0pt;font-family:Consolas;mso-fareast-language:EN-US">over</span><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">, maybe a name like
</span><span lang="EN-GB" style="font-size:11.0pt;font-family:Consolas;mso-fareast-language:EN-US">stackswap</span><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"> could be preferable?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">Jochem<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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