8.1. Lesson: ラスターデータで作業する



このレッスンの目標: QGISでラスターデータを操作する方法を学習します。

8.1.1. basic Follow Along: ラスターデータを読み込む

Raster data can be loaded with the same methods we used for vector data. However we suggest to use the Browser Panel.

  1. Open the Browser Panel and expand the exercise_data/raster folder.

  2. Load all the data in this folder:

    • 3320C_2010_314_RGB_LATLNG.tif

    • 3320D_2010_315_RGB_LATLNG.tif

    • 3420B_2010_328_RGB_LATLNG.tif

    • 3420C_2010_327_RGB_LATLNG.tif

You should see the following map:



8.1.2. basic Follow Along: 仮想ラスターの作成


Luckily, QGIS allows you to do exactly this, and without needing to actually create a new raster file, which could take up a lot of space. Instead, you can create a Virtual Raster. This is also often called a Catalog, which explains its function. It's not really a new raster. Rather, it's a way to organize your existing rasters into one catalog: one file for easy access.

To make a catalog we will use the Processing ‣ Toolbox.

  1. Open the Build virtual raster algorithm from the GDAL ‣ Raster miscellaneous;

  2. In the dialog that appears click on the ... button next to the Input layers parameter and check all the layers or use the Select All button;

  3. Uncheck the Place each input file into a separate band parameter- Notice the text field below. What this dialog is actually doing is that it's writing that text for you. It's a long command that QGIS is going to run.


    Keep in mind that you can copy and paste the text in the OSGeo Shell (Windows user) or Terminal (Linux and OSX users) to run the command. You can also create a script for each GDAL command. This is very handy when the procedure is taking a long time or when you want to schedule specific tasks. Use the Help button to get more help on the syntax of GDAL commands.

  4. Finally click on Run.


As you know from the previous modules, Processing creates temporary layers by default. To save the file click on the ... button.


You can now remove the original four rasters from the Layers Panel and leave only the output virtual catalog raster.

8.1.3. hard ラスターデータの変換

上記の方法では、カタログを使用してデータセットを仮想的にマージし、それらを「その場で」再投影できます。しかし、もし長期間使用することになるデータを用意しているならば、マージされ再投影された新しいラスターを作成する方が効率的かもしれません。はじめに用意をするのに少し時間がかかりますが、そうしておけば地図でラスターを使う際のパフォーマンスが向上します。 ラスターを再投影する

Open Warp (reproject) from GDAL ‣ Raster projections.

You can also reproject virtual rasters (catalogs), enable multithreaded processing, and more.

../../../_images/warp_rasters.png ラスターをマージする

If you need to create a new raster layer and save it to disk you can use the merge algorithm.


Depending on how many raster files you are merging and their resolution, the new raster file created can be really big. Consider instead to create a raster catalog as described in the Create a Virtual Raster section.

  1. Click on the Merge algorithm from the GDAL ‣ Raster miscellaneous menu.

  2. As we did for the Create a Virtual raster, use the ... button to choose which layers you want to merge.

    You can also specify a Virtual raster as input, and then all of the rasters that it consists of will be processed.

  3. If you know the GDAL library, you can also add your own options by opening the Advanced parameters menu.


8.1.4. In Conclusion


8.1.5. What's Next?