man: Improve segment library documentation, provide examples by wenzeslaus · Pull Request #20 · OSGeo/grass

wenzeslaus · 2019-05-24T03:22:55Z

This PR adds two examples into doc/examples which can be compiled as GRASS modules and executed. It adds 3 new sections to the library dox file: about general use with raster, about use with list of rasters (includes portions of one of the examples, so the code is only at one place), and a complete example (here including whole files). Finally, it modifies documentation for two functions.

Besides asking for general review of best practices in using this library, I'm asking these two questions:

Is the remark about value initialization correct? (I don't really see a point in using calloc instead of malloc there considering that the non-memory case does initialize with zeros.)
What about the precondition for Segment_get_row()? Does Segment_get() need the same one? Segment_flush() description suggests that only writing to disk and Segment_get_row() need that and Segment_get_row() does not call any page function if that has any influence.

metzm · 2019-05-24T06:31:50Z

doc/raster/r.example.segment/main.c

+
+    /* determine the input map type (CELL/FCELL/DCELL) */
+    map_type = Rast_map_type(input_name, "");
+    size_t cell_size = Rast_cell_size(map_type);


move "size_t cell_size;" up, just after "RASTER_MAP_TYPE map_type;"

metzm · 2019-05-24T06:32:30Z

doc/raster/r.example.segment/main.c

+    ncols = Rast_window_cols();
+
+    /* size of a segment */
+    int srows = 64;


Move "int srows, scols, num_seg;" up

metzm · 2019-05-24T06:33:16Z

doc/raster/r.example.segment/main.c

+    int num_seg = 4;
+
+    /* segment structure */
+    SEGMENT raster_seg;


move "SEGMENT raster_seg;" up

metzm · 2019-05-24T06:35:48Z

doc/raster/r.example.segmulti/main.c

+
+    /* pass the pointer, set the value */
+    Segment_put(raster_seg, values, row, col);
+}


G_free(values):

metzm · 2019-05-24T06:36:45Z

doc/raster/r.example.segmulti/main.c

+    ncols = Rast_window_cols();
+
+    /* size of a segment */
+    int srows = 64;


as for r.example.segment, move int srows, sclos, nsegs; up

metzm · 2019-05-24T06:37:17Z

doc/raster/r.example.segmulti/main.c

+    int nsegs = 4;
+
+    map_type = DCELL_TYPE;
+    size_t cell_size = Rast_cell_size(map_type);


Move "size_t cell_size, segment_cell_size;" up

metzm · 2019-05-24T06:37:28Z

doc/raster/r.example.segmulti/main.c

+    output_fd = Rast_open_new(output_name, map_type);
+
+    /* segment structure */
+    SEGMENT raster_seg;


metzm · 2019-05-24T06:37:50Z

doc/raster/r.example.segmulti/main.c

+        G_fatal_error(_("Unable to create temporary segment file"));
+
+    /* array to store file descriptors */
+    int *input_fds = G_malloc(ninputs * sizeof(int));


move "int *input_fds;" up

metzm · 2019-05-24T06:38:14Z

doc/raster/r.example.segmulti/main.c

+    }
+
+    /* allocate input buffer */
+    DCELL *row_buffer = Rast_allocate_d_buf();


move "DCELL *row_buffer, *seg_buffer;" up

metzm · 2019-05-24T06:38:48Z

doc/raster/r.example.segmulti/main.c

+
+    /* pass the pointer, set the value */
+    Segment_put(raster_seg, values, row, col);
+}


G_free(values);

metzm · 2019-05-24T06:39:19Z

doc/raster/r.example.segmulti/r.example.segmulti.html

+
+<em>
+<a href="r.example.html">r.example</a>
+<a href="r.example.html">r.example.segment</a>


r.example.segment.html

metzm · 2019-05-24T06:41:12Z

lib/segment/get_row.c

- * <b>Buf</b> will be filled with <em>ncols*len</em> bytes of data
- * corresponding to the <b>row</b> in the data matrix.
+ * \pre *buf* points to an allocated array of length <em>ncols*len</em>
+ * where *len* is size of one stored value (cell).


e.g. cell or a custom data structure

metzm · 2019-05-24T06:42:54Z

lib/segment/open.c

+ * Segment_init(), all-in-memory mode initialization, and temporary
+ * file handling.
+ *
+ * The values are not guaranteed to be initialized to zero or NULL.


not values, but bytes, they are indeed initialized to zero because of lseek and calloc

metzm · 2019-05-24T06:44:30Z

lib/segment/segmentlib.dox

+the raster you need to access:
+
+\code
+for (int row = 0; row < Rast_window_rows(); row++) {


for (int row = 0; ...) is C++ style

metzm · 2019-05-24T06:47:47Z

lib/segment/segmentlib.dox

+
+\skip G_free
+\until Rast_close(output_fd);
+


Segment_close() ?

metzm · 2019-05-24T06:54:28Z

This PR adds two examples into doc/examples which can be compiled as GRASS modules and executed. It adds 3 new sections to the library dox file: about general use with raster, about use with list of rasters (includes portions of one of the examples, so the code is only at one place), and a complete example (here including whole files). Finally, it modifies documentation for two functions.

Please use standard C style in sample code.
Maybe documentation does not need to be that long? avoid tl;dr

Besides asking for general review of best practices in using this library, I'm asking these two questions:
* Is the remark about value initialization correct? (I don't really see a point in using calloc instead of malloc there considering that the non-memory case does initialize with zeros.)

See "man calloc". malloc does not initialize the memory while calloc does.

* What about the precondition for `Segment_get_row()`? Does `Segment_get()` need the same one?

No.

Segment_flush() description suggests that only writing to disk and Segment_get_row() need that and Segment_get_row() does not call any page function if that has any influence.

Yes, that's the reason: Segment_get_row() bypasses the internal cache and reads directly from the temporary file.

metzm · 2019-05-24T20:23:51Z

Considering examples on how to use the segment library, it is IMHO sufficient to mention current working modules like r.cost, r.walk, r.watershed, r.stream.extract.

mlennert · 2019-05-29T12:34:42Z

Jumping into this discussion a bit late, so just two short comments:

I think we definitely need enhanced and detailed documentation of the C-code. @metzm, today you are probably the only one to really know the nitty-gritty stuff in this library, so for future sustainability (and possibly attracting the rare C-developer out there), good doc seems a must to me.
At this stage, I haven't had the chance to delve into the doc enough to understand whether new (simple) examples are needed. They have the advantage of focusing on the features documented, thus avoiding distraction through other unrelated parts of code. They have the disadvantage of having to be updated when the library changes. Actual production modules obviously provide more motivation to keep them up to date.

I don't think this has been done as such in the code doc, yet, but maybe we could just add specific references to the existing production modules directly into the doc ?

wenzeslaus · 2020-11-10T18:01:55Z

Note to myself: It seems that it worth explicitly noting that functions such as Segment_get() don't do bounds check for row and col (and thus crash will occur rather than an error message).

neteler · 2023-11-07T12:46:19Z

@wenzeslaus would you mind to rebase this PR?

echoix · 2024-06-21T21:32:02Z

@wenzeslaus I manually resolved the conflicts

doc/raster/r.example.segment/main.c

doc/raster/r.example.segmulti/main.c

lib/segment/get_row.c

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

doc/raster/r.example.segment/README.md

doc/raster/r.example.segmulti/README.md

echoix

@wenzeslaus is this still relevant now? It is currently in a state where it up to date enough to pass CI, but there are still some very old (6 years) review comments.

Also, could you take a new look, to tell us if it still shows the patterns we want to show as an example?

It's kind of funny to still see the issue/pr number #20, that is still open. Probably the oldest we have open. Edit: it is the oldest open PR or issue we have

echoix

It is our oldest open PR, number 20. We have to port the docs changes in HTML to markdown. Also, since the last update of the PR, the folder structure changed (in early January 2025, in #4815)

echoix · 2025-02-26T17:23:59Z

doc/raster/r.example.segment/r.example.segment.html

Remember to apply the changes in a new markdown file when updating the PR.

echoix · 2025-02-26T17:24:39Z

doc/raster/r.example.segmulti/r.example.segmulti.html

Remember to apply the changes in a new markdown file when updating the PR.

Abhi-d-gr8 · 2026-02-04T02:46:34Z

Hi! @wenzeslaus and @echoix, I was just seeing the oldest PRs for fun and found that this was stuck on some old merge conflicts and needed the docs converted to Markdown, so I decided to take a look ...

I've gone ahead and rebased this work and converted the docs to Markdown to resolve the conflicts.
To keep things clean, I opened a fresh PR : #7035

wenzeslaus added 3 commits May 23, 2019 17:48

doc: examples for Segmement Library in dox and as code

52a9359

doc: advanced example for segmentlib in dox from example code

acd56eb

doc: improved desc for open and get_row in segmentlib

08f9480

wenzeslaus added the enhancement New feature or request label May 24, 2019

wenzeslaus requested a review from metzm May 24, 2019 03:22

metzm reviewed May 24, 2019

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doc/raster/r.example.segment/main.c

int num_seg = 4;

/* segment structure */

SEGMENT raster_seg;

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move "SEGMENT raster_seg;" up

metzm reviewed May 24, 2019

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lib/segment/segmentlib.dox

\skip G_free

\until Rast_close(output_fd);

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Segment_close() ?

wenzeslaus added this to the 8.2.0 milestone Dec 2, 2021

wenzeslaus modified the milestones: 8.2.0, 8.4.0 Feb 27, 2022

wenzeslaus modified the milestones: 8.3.0, 8.4.0 Feb 10, 2023

HuidaeCho assigned wenzeslaus Mar 6, 2024

wenzeslaus modified the milestones: 8.4.0, 8.5.0 Apr 26, 2024

Merge branch 'main' into segment-lib-doc

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github-actions bot added C Related code is in C HTML Related code is in HTML libraries docs labels Jun 21, 2024

github-actions bot reviewed Jun 21, 2024

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Apply suggestions from clang-format

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Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

echoix changed the title ~~Improve segment library documentation, provide examples~~ man: Improve segment library documentation, provide examples Jun 21, 2024

echoix added 3 commits June 25, 2024 23:26

Merge branch 'main' into segment-lib-doc

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Merge branch 'main' into segment-lib-doc

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Merge branch 'main' into segment-lib-doc

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echoix reviewed Dec 21, 2024

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echoix added 2 commits December 20, 2024 19:22

Add language in markdown fenced code blocks

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Merge branch 'main' into segment-lib-doc

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echoix reviewed Dec 21, 2024

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doc/raster/r.example.segmulti/README.md Outdated Show resolved Hide resolved

Update README.md

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echoix reviewed Dec 21, 2024

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echoix requested changes Feb 26, 2025

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echoix added the conflicts/needs rebase Rebase to or merge with the latest base branch is needed label Feb 26, 2025

Merge branch 'main' into segment-lib-doc

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github-actions bot added the markdown Related to markdown, markdown files label Aug 9, 2025

Merge branch 'main' into segment-lib-doc

9d01154

wenzeslaus modified the milestones: 8.5.0, 8.6.0 Dec 15, 2025

Abhi-d-gr8 mentioned this pull request Feb 4, 2026

doc: Modernize segment library examples and documentation #7035

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metzm commented May 24, 2019

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