Mengonversi dari satu CRS/proyeksi ke yang lain

Proses mengonversi dari satu CRS atau proyeksi ke lainnya ditangani oleh metode spTransform() dalam paket rgdal. spTransform() memiliki metode untuk semua objek sp termasuk SpatialPolygonsDataFrame, tetapi tidak berfungsi pada objek raster. Ini karena transformasi raster sedikit lebih rumit; grid persegi panjang yang ditransformasikan tidak lagi berbentuk persegi panjang. Anda dapat melihat ?raster::projectRaster jika Anda ingin tahu tentang cara mentransformasikan raster.

Transformasi itu sederhana. Argumen pertama untuk spTransform(), x, adalah objek spasial yang akan ditransformasikan dan argumen kedua, CRS, adalah spesifikasi CRS yang diinginkan. CRS dapat ditentukan dengan string PROJ4, yang bisa Anda susun secara manual, tetapi jauh lebih mudah mengambilnya dari objek yang sudah ada (misalnya dengan fungsi proj4string()).

Saatnya membuat kedua himpunan data poligon Anda berada dalam CRS yang sama.

Latihan ini adalah bagian dari kursus

Memvisualisasikan Data Geospasial di R

Petunjuk latihan

Transformasikan neighborhoods agar memiliki CRS yang sama dengan nyc_tracts menggunakan spTransform() dengan argumen CRS disetel ke proj4string(nyc_tracts).
Verifikasi transformasi dengan melihat head() dari coordinates(neighborhoods).
Periksa apakah himpunan data kini selaras dengan memplot neighborhoods, lalu memplot nyc_tracts dengan add = TRUE dan col = "red", dan terakhir memplot water dengan add = TRUE dan col = "blue".

Latihan interaktif praktis

Cobalah latihan ini dengan menyelesaikan kode contoh berikut.

library(sp)
library(raster)

# Use spTransform on neighborhoods: neighborhoods



# head() on coordinates() of neighborhoods


# Plot neighborhoods, nyc_tracts and water

Edit dan Jalankan Kode

Latihan ini adalah bagian dari kursus

Memvisualisasikan Data Geospasial di R

SkillTag.level.intermediateSkillTag.label

4.6+

Mulai Kursus Gratis

We'll dive in by displaying some spatial data -- property sales in a small US town -- using ggplot2 and we'll introduce you to the ggmap package as a quick way to add spatial context to your plots. We'll talk about what makes spatial data special and introduce you to the common types of spatial data we'll be working with throughout the course.

Exercise 1: Introduction to spatial data Exercise 2: Grabbing a background map Exercise 3: Putting it all together Exercise 4: Insight through aesthetics Exercise 5: Useful get_map() and ggmap() options Exercise 6: Different maps Exercise 7: Leveraging ggplot2's strengths Exercise 8: A quick alternative Exercise 9: Common types of spatial data Exercise 10: Drawing polygons Exercise 11: Choropleth map Exercise 12: Raster data as a heatmap

You can get a long way with spatial data stored in data frames, but it makes life easier if they are stored in special spatial objects. In this chapter we'll introduce you to the spatial object classes provided by the sp package, particularly for point and polygon data. You'll learn how to explore and subset these objects by exploring a world map. The reward for learning about these object classes: we'll show you the package tmap which requires spatial objects as input, but makes creating maps really easy! You'll finish up by making a map of the world's population.

Exercise 1: Introducing sp objects Exercise 2: Let's take a look at a spatial object Exercise 3: What's inside a spatial object?Exercise 4: A more complicated spatial object Exercise 5: sp and S4 Exercise 6: Walking the hierarchy Exercise 7: Further down the rabbit hole Exercise 8: More sp classes and methods Exercise 9: Subsetting by index Exercise 10: Accessing data in sp objects Exercise 11: Subsetting based on data attributes Exercise 12: tmap, a package that works with sp objects Exercise 13: Introduction to tmap Exercise 14: Building a plot in layers Exercise 15: Why is Greenland so big?Exercise 16: Saving a tmap plot

While the sp package provides some classes for raster data, the raster package provides more useful classes. You'll be introduced to these classes and their advantages and then learn to display them. The examples continue with the theme of population from Chapter 2, but you'll look at some much finer detail datasets, both spatially and demographically. In the second half of the chapter you'll learn about color -- an essential part of any visual display, but especially important for maps.

Exercise 1: The raster package Exercise 2: What's a raster object?Exercise 3: Some useful methods Exercise 4: A more complicated object Exercise 5: A package that uses Raster objects Exercise 6: Color scales Exercise 7: Pick the right palette Exercise 8: Adding a custom continuous color palette to ggplot2 plots Exercise 9: Custom palette in tmap Exercise 10: More about color scales Exercise 11: An interval scale example Exercise 12: A diverging scale example Exercise 13: A qualitative example

In this chapter you'll follow the creation of a visualization from raw spatial data files to adding a credit to a map. Along the way, you'll learn how to read spatial data into R, more about projections and coordinate reference systems, how to add additional data to a spatial object, and some tips for polishing your maps.

Exercise 1: Membaca data spasial Exercise 2: Membaca shapefile Exercise 3: Membaca berkas raster Exercise 4: Mengambil data menggunakan sebuah paket Exercise 5: Sistem referensi koordinat Exercise 6: Menggabungkan data dari CRS/proyeksi yang berbeda Exercise 7: Mengonversi dari satu CRS/proyeksi ke yang lain

Latihan Saat Ini

Exercise 8: Menambahkan data ke objek spasial Exercise 9: Cara yang keliru Exercise 10: Memeriksa kecocokan data Exercise 11: Menggabungkan atribut data Exercise 12: Plot pertama Exercise 13: Memoles peta Exercise 14: Menyeleksi subset neighborhoods Exercise 15: Menambahkan label lingkungan Exercise 16: Merapikan legenda dan beberapa penyesuaian akhir Exercise 17: Ringkasan