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+ +
+

Push coordinate value to pipeline stack

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+

New in version 6.0.0.

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+

Save components of a coordinate from one step of a pipeline and make it +available for retrieving in another pipeline step.

+ ++++ + + + + + + + + + + + + + + +

Alias

push

Domain

4D

Input type

Any

Output type

Any

+

This operations allows for components of coordinates to be saved for +application in a later step. A saved coordinate component is moved, or +pushed, to a memory stack that is part of a pipeline. The +pipeline coordinate stack is inspired by the stack data structure that is +commonly used in computer science. There’s four stacks available: One four each +coordinate dimension. The dimensions, or coordinate components, are numbered +1–4. It is only possible to move data to and from the stack within the same +coordinate component number. Values can be moved off the stack again by using +the pop operation.

+

If the push operation is used by itself, e.g. not in a pipeline, it will +function as a no-operation that passes the coordinate through unchanged.

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+

Examples

+

A common use of the push and pop operations is in 3D +Helmert transformations where only the horizontal components +are needed. This is often the case when combining heights from a legacy +vertical reference with a modern geocentric reference. Below is a an example of +such a transformation, where the horizontal part is transformed with a Helmert +operation but the vertical part is kept exactly as the input was.

+
$ echo 12 56 12.3 2020 | cct +proj=pipeline  \
++step +proj=push +v_3                        \
++step +proj=cart +ellps=GRS80                \
++step +proj=helmert +x=3000 +y=1000 +z=2000  \
++step +proj=cart +ellps=GRS80 +inv           \
++step +proj=pop +v_3                         \
+
+ 12.0056753463   55.9866540552       12.3000     2000.0000
+
+
+

Note that the third coordinate component in the output is the same as the input.

+

The same transformation without the push and pop operations would look like this:

+
$ echo 12 56 12.3 2020 | cct +proj=pipeline  \
++step +proj=cart +ellps=GRS80                \
++step +proj=helmert +x=3000 +y=1000 +z=2000  \
++step +proj=cart +ellps=GRS80 +inv           \
+
+      12.0057        55.9867     3427.7404     2000.0000
+
+
+

Here the vertical component is adjusted significantly.

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Parameters

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+
++v_1
+

Stores the first coordinate component on the pipeline stack

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+ +
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++v_2
+

Stores the second coordinate component on the pipeline stack

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+ +
+
++v_3
+

Stores the third coordinate component on the pipeline stack

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+ +
+
++v_4
+

Stores the fourth coordinate component on the pipeline stack

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+ +
+
+

Further reading

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    +

  1. Stack data structure on Wikipedia

    2. +
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