Refactor description of sf interfaces, big it up #743

Robinlovelace · 2022-02-04T10:08:33Z

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Robinlovelace · 2022-02-04T11:09:10Z

This can basically close #705 bringing us close to submission of part 1 for peer review. Is anyone up for adding content to C5 of geometry operations to match this? Not essential but maybe worth mentioning in passing.

Nowosad · 2022-02-05T11:48:45Z

02-spatial-data.Rmd

@@ -108,7 +108,16 @@ knitr::include_graphics(c("figures/vector_lonlat.png", "figures/vector_projected
 ```

 **sf** is a package providing classes for geographic vector data.
-Not only does **sf** supersede **sp**, it also provides a consistent command-line interface to GEOS\index{GEOS} and GDAL\index{GDAL}, superseding **rgeos** and **rgdal** (described in Section \@ref(the-history-of-r-spatial)).


@Robinlovelace one overall comment that came to mind yesterday -- maybe we could limit mentions of sp to minimum in the main text, and leave it to footnotes (as we already have dropped it from the first edition of the book)...

Nowosad · 2022-02-05T11:51:47Z

02-spatial-data.Rmd

-Not only does **sf** supersede **sp**, it also provides a consistent command-line interface to GEOS\index{GEOS} and GDAL\index{GDAL}, superseding **rgeos** and **rgdal** (described in Section \@ref(the-history-of-r-spatial)).
+Not only does **sf** supersede **sp**, it also provides a consistent command-line interface to five important low level libraries for geocomputation:
+
+- GEOS\index{GEOS}, for geometry operations such as calculating buffers and centroids, covered in Chapter \@ref(geometric-operations)


I would suggest different order of the libraries: start with GDAL, then PROJ, then GEOS and S2. I am also unsure if we should list liblwgeom here, as it is not mentioned in the sf intro message...

I suggested different order partially to keep GEOS and S2 together as they have overlapping capabilities but for data with different CRSs

Nowosad · 2022-02-05T11:52:22Z

02-spatial-data.Rmd

+- [S2](https://s2geometry.io/), a spherical geometry engine written in C++ developed by Google, via the [**s2**](https://r-spatial.github.io/s2/) package, covered in Section \@ref(s2) below and in Chapter \@ref(reproj-geo-data)
+
+Information about these interfaces is provided by **sf** the first time the package is loaded, explaining the meaning of the text `Linking to GEOS 3.8.0, GDAL 3.0.4, PROJ 6.3.1; sf_use_s2() is TRUE` that appears below the `library(sf)` command at the beginning of this chapter.
+**sf** is the only package/system *in any language* that provides a unified interface to this wide range of high performance functionality from an interactive command-line environment for reproducible research.


Maybe it would be worth to say "is currently"

Nowosad · 2022-02-05T11:53:41Z

02-spatial-data.Rmd

 ```{r vector-crs, echo=FALSE, fig.cap="Examples of geographic (WGS 84; left) and projected (NAD83 / UTM zone 12N; right) coordinate systems for a vector data type.", message=FALSE, fig.asp=0.56, fig.scap="Examples of geographic and projected CRSs (vector data)."}
 # source("https://github.com/Robinlovelace/geocompr/raw/main/code/02-vector-crs.R")
 knitr::include_graphics("figures/02_vector_crs.png")
 ```

+### Spherical geometry operations with S2 {#s2}


Should not this subsection be in the vector data section? S2 only works on spatial vectors...

Nowosad · 2022-02-05T12:53:18Z

02-spatial-data.Rmd

-Not only does **sf** supersede **sp**, it also provides a consistent command-line interface to GEOS\index{GEOS} and GDAL\index{GDAL}, superseding **rgeos** and **rgdal** (described in Section \@ref(the-history-of-r-spatial)).
+Not only does **sf** supersede **sp**, it also provides a consistent command-line interface to five important low level libraries for geocomputation:
+
+- GEOS\index{GEOS}, for geometry operations such as calculating buffers and centroids, covered in Chapter \@ref(geometric-operations)


I suggested different order partially to keep GEOS and S2 together as they have overlapping capabilities but for data with different CRSs

Nowosad · 2022-02-05T12:54:30Z

02-spatial-data.Rmd

@@ -774,6 +782,42 @@ sf::st_crs(df_sf) = 4326
 It is fast and reliable at 'casting' geometry columns to different types, a topic covered in Chapter \@ref(geometric-operations).
 Benchmarks, in the package's [documentation](https://dcooley.github.io/sfheaders/articles/examples.html#performance) and in test code developed for this book, show it is much faster than the `sf` package for such operations.

+### Spherical geometry operations with S2 {#s2}


BTW -- do we mention what is a "planar geometry" anywhere is the book?

Nowosad · 2022-02-05T13:39:28Z

02-spatial-data.Rmd

 - GDAL\index{GDAL}, for reading, writing and manipulating a wide range of geographic data formats, covered in Chapter \@ref(read-write)
+- GEOS\index{GEOS}, for geometry operations such as calculating buffers and centroids, covered in Chapter \@ref(geometric-operations)


"calculating buffers and centroids on data with a projected CRS" (or similar)?

Robinlovelace · 2022-02-05T14:04:44Z

Heads-up @Nowosad I've updated the intro to sf and its interfaces thanks to your comments. As of most recent commit it says:

sf provides classes for geographic vector data and a consistent command-line interface to important low level libraries for geocomputation:

PROJ, a powerful library for coordinate system transformations, which underlies the content covered in Chapter @ref(reproj-geo-data)
GDAL\index{GDAL}, for reading, writing and manipulating a wide range of geographic data formats, covered in Chapter @ref(read-write)
GEOS\index{GEOS}, a planar geometry engine for operations such as calculating buffers and centroids on data with a projected CRS, covered in Chapter @ref(geometric-operations)
S2, a spherical geometry engine written in C++ developed by Google, via the s2 package, covered in Section @ref(s2) below and in Chapter @ref(reproj-geo-data)

At the time of writing (2022), sf is the only package in any language that provides a unified command line interface (CLI) to this wide range of geographic libraries in an interactive environment for data science.
Information about these interfaces is printed by sf the first time the package is loaded: the message Linking to GEOS 3.8.0, GDAL 3.0.4, PROJ 6.3.1; sf_use_s2() is TRUE that appears below the library(sf) command at the beginning of this chapter tells us the versions of linked GEOS, GDAL and PROJ libraries (these vary between computers and over time) and whether or not the S2 interface is turned on.
A unique feature of sf is that you can change switch the default geometry engine used on unprojected data: 'switching off' S2 can be done with the command sf::sf_use_s2("FALSE"), meaning that the planar geometry engine GEOS will be used by default for all geometry operations, including geometry operations on unprojected data.
As we will see in Section @ref(s2), planar geometry is based on 2 dimensional space.
Planar geometry engines such as GEOS assume 'flat' (projected) coordinates while spherical geometry engines such as S2 assume unprojected (lon/lat) coordinates.

Nowosad · 2022-02-05T14:07:43Z

👍🏻

Nowosad · 2022-02-05T14:08:06Z

Feel free to merge it.

Robinlovelace · 2022-02-05T14:14:36Z

Thanks for the review. Merging 🚀

jannes-m · 2022-02-05T20:46:17Z

I would tone down since e. g., Postgis also makes use of gdal, geos and proj (among others) and an s2 extension is also available. And I would guess the same is true for Grass and if it does not support s2, well, then most certainly it supports. an ellipsoidal representation of the Earth. Qgis is using the same libraries and there is also some s2 support (only did a very quick check). Postgis, Grass and QGIS also provide command line interfaces (Python and SQL).

Robinlovelace · 2022-02-06T09:46:42Z

Thanks for the feedback @jannes-m. Can you put in a PR or just commit to the main branch that tones it down?

Robinlovelace · 2022-02-06T09:47:05Z

PR preferred here as it allows conversation and iteration before making the change.

Refactor description of sf interfaces, big it up

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Robinlovelace mentioned this pull request Feb 4, 2022

Introduce s2, show how to turn it on and off, mention consequences #705

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Robinlovelace added 2 commits February 4, 2022 10:12

Add placeholder s2 section for #705

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Cross refs to S2 content for #705

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Robinlovelace mentioned this pull request Feb 4, 2022

Math not working in browser for sf7 r-spatial/sf#1898

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Big progress on s2 for #705

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Robinlovelace marked this pull request as ready for review February 4, 2022 11:08

Robinlovelace requested review from Nowosad and jannes-m February 4, 2022 11:08

Robinlovelace added 2 commits February 4, 2022 15:38

Shorten sentence, rather than *just* concepts

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Update outdated exercise 1

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Robinlovelace added 3 commits February 5, 2022 12:38

Tweaks after review by @Nowosad

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Update chapter order, mention s2, close #705

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Add note

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Robinlovelace requested a review from Nowosad February 5, 2022 12:46

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Update order of sf interfaces

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Robinlovelace and others added 4 commits February 5, 2022 13:45

Shorten sentence

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Update 02-spatial-data.Rmd

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Define planar geometry, tweak intro to sf

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Merge branch 's2-2022' of github.com:Robinlovelace/geocompr into s2-2022

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Put GDAL before PROJ

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Robinlovelace merged commit c3729d9 into main Feb 5, 2022

Robinlovelace deleted the s2-2022 branch February 5, 2022 14:15

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Refactor description of sf interfaces, big it up #743

Refactor description of sf interfaces, big it up #743

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Robinlovelace commented Feb 6, 2022

		- GDAL\index{GDAL}, for reading, writing and manipulating a wide range of geographic data formats, covered in Chapter \@ref(read-write)
		- GEOS\index{GEOS}, for geometry operations such as calculating buffers and centroids, covered in Chapter \@ref(geometric-operations)

Refactor description of sf interfaces, big it up #743

Refactor description of sf interfaces, big it up #743

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