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20. 예제 데이터 준비

참고

강의 담당자나 숙련된 QGIS 사용자가 강의에 로컬 샘플 데이터를 이용하고자 할 경우 이 준비 과정이 필요합니다. 교육 교재와 함께 기본 데이터셋이 제공되지만, 기본 데이터셋을 로컬 데이터로 대체하고자 한다면 다음 지침을 따라야 합니다.

교육 교재와 함께 제공되는 샘플 데이터 는 Swellendam 마을 및 그 주변에 대한 자료입니다. Swellendam 은 남아프리카 공화국의 웨스턴케이프에 있는 케이프타운에서 동쪽으로 2시간 거리에 있습니다. 이 데이터셋의 피처명은 영어와 아프리칸스어 두 가지로 되어 있습니다.

누구나 이 데이터셋을 어려움없이 이용할 수 있습니다. 그러나 사용자 자국 또는 고향의 데이터를 이용하고자 할 경우, 모듈 3에서 모듈 7.2까지의 모든 강의에 사용자의 데이터를 쓸 수 있습니다. 이후 강의에는 좀더 복잡한 데이터 소스를 사용하게 되는데, 사용자의 지역에 따라 이런 데이터가 존재하지 않을 수도 있습니다.

참고

이 지침은 사용자가 QGIS를 잘 알고 있다고 가정하며, 강의 교재로 쓰이도록 작성된 것은 아닙니다.

20.1. ★★★ Try Yourself: Create OSM based vector files

사용자의 강의에 기본 데이터셋 대신 로컬 데이터를 사용하고자 할 경우 QGIS에 내장된 도구로 간단히 데이터를 준비할 수 있습니다. 이때 사용자가 선택한 지역은 도심과 교외가 균형 있게 분포하며, 서로 다른 종류의 도로와 (자연보호구역 또는 농장 같은) 지역 경계, 그리고 하천 같은 지표수를 포함해야 합니다.

  1. 새 QGIS 프로젝트 열기

  2. Select Layer ► Data Source Manager to open the Data Source Manager dialog

  3. In the Browser tab, expand the XYZ Tiles drop-down menu and double-click the OpenStreetMap item.

    ../../../_images/browser_xyztiles.png

    A map of the world is now visible on the map canvas.

  4. Close the Data Source Manager dialog

  5. Move to the area you’d like to use as study area

    ../../../_images/swellendam_neighborhood.png

Now that we have the area we’ll extract the data from, let’s enable the extraction tools.

  1. Go to Plugins ► Manage/Install Plugins…

  2. In the All tab, type QuickOSM in the search box

  3. Select the QuickOSM plugin, press Install Plugin and then Close the dialog.

    ../../../_images/quickosm_plugin_download.png

  4. Execute the new plugin from Vector ► QuickOSM ► QuickOSM… menu

  5. In the Quick query tab, select building in the Key drop-down menu

  6. Leave the Value field empty, meaning that you are querying all buildings.

  7. Select Canvas Extent in the next drop-down menu

  8. Expand the Advanced group below and uncheck all geometry types on the right except Multipolygons.

  9. Press Run query

    ../../../_images/building_query_builder.png

    A new building layer is added to the Layers panel, showing buildings in the selected extent.

  10. Proceed as above to extract other data:

    1. Key = landuse and Multipolygons geometry type.

    2. Key = boundary, Value = protected_area and Multipolygons geometry type.

    3. Key = natural, Value = water and Multipolygons geometry type.

    4. Key = highway and check Lines and Multilines geometry types.

    5. Key = waterway, Value = river and check Lines and Multilines geometry types.

    6. Key = place and Points geometry type.

This process adds the layers as temporary files (indicated by the indicatorMemory icon next to their name).

../../../_images/osm_data_loaded.png

You can sample the data your region contains in order to see what kind of results your region will yield.

We now need to save the resulting data to use during your course. We’ll be using ESRI Shapefile, GeoPackage and SpatiaLite formats depending on the data.

To convert the place temporary layer to another format:

  1. Click the indicatorMemory icon next to the place layer to open the Save Scratch Layer dialog.

    참고

    If you need to change any of the temporary layer’s properties (CRS, extent, fields…), use the Export ► Save Features as… contextual menu instead, and ensure the Add saved file to map option is checked. This adds a new layer.

  2. Select the ESRI Shapefile format

  3. Use the … button to browse to the exercise_data/shapefile/ folder and save the file as places.shp.

    ../../../_images/save_osm_place.png

  4. OK 를 클릭하십시오.

    In the Layers panel, the temporary place layer is replaced with the saved places shapefile layer and the temporary icon next to it removed.

  5. Double-click the layer to open its Layer Properties ► Source tab and update the Layer name property to match the file name.

  6. Repeat the process for other layers, renaming them as follows:

    • natural_water into water

    • waterway_river into rivers

    • boundary_protected_area into protected_areas

    Each resulting data set should be saved in the exercise_data/shapefile/ directory.

The next step is to create a GeoPackage file from the building layer to use during the course:

  1. Click the indicatorMemory icon next to the building layer

  2. Select the GeoPackage format

  3. Save the file as training_data.gpkg under the exercise_data/ folder

  4. By default, the Layer name is filled as the file name. Replace it with buildings.

    ../../../_images/save_osm_building.png

  5. OK 를 클릭하십시오.

  6. Rename the layer in its properties dialog

  7. Repeat the process with the highway layer, saving it as roads in the same GeoPackage database.

The last step is to save the remaining temporary file as a SpatiaLite file.

  1. Click the indicatorMemory icon next to the landuse layer

  2. Select the SpatiaLite format

  3. Save the file as landuse.sqlite under the exercise_data/ folder. By default, the Layer name is filled as the file name. Do not change it.

    ../../../_images/save_osm_landuse.png

  4. OK 를 클릭하십시오.

You should now have a map which looks something like this (the symbology will certainly be very different, because QGIS randomly assigns colors when layers are added to the map):

../../../_images/post_osm_import.png

The important thing is that you have 7 vector layers matching those shown above and that all those layers have some data.

20.2. ★★★ Try Yourself: Create SRTM DEM tiff files

For modules Module: Creating Vector Data and Module: Rasters, you’ll also need raster images (SRTM DEM) which cover the region you have selected for your course.

The CGIAR-CGI provides some SRTM DEM you can download from https://srtm.csi.cgiar.org/srtmdata/.

You’ll need images which cover the entire region you have chosen to use. To find the extent coordinates, in QGIS , zoomToLayer zoom to the extent of the largest layer and pick the values in the extents Extents box of the status bar. Keep the GeoTiff format. Once the form is filled, click on the Click here to Begin Search >> button and download the file(s).

Once you have downloaded the required file(s), they should be saved in the exercise_data directory, under raster/SRTM subfolders.

20.3. ★★★ Try Yourself: Create imagery tiff files

In Module Module: Creating Vector Data, ★☆☆ Follow Along: Data Sources lesson shows close-up images of three school sports fields which students are asked to digitize. You’ll therefore need to reproduce these images using your new SRTM DEM tiff file(s). There is no obligation to use school sports fields: any three school land-use types can be used (e.g. different school buildings, playgrounds or car parks).

For reference, the image in the example data is:

../../../_images/field_outlines.png

20.4. ★☆☆ Try Yourself: Replace tokens

Having created your localized dataset, the final step is to replace the tokens in the substitutions.txt file so that the appropriate names will appear in your localized version of the Training Manual.

교체해야 할 표식들은 다음과 같습니다.

  • majorUrbanName: this defaults to “Swellendam”. Replace with the name of the major town in your region.

  • schoolAreaType1: this defaults to “athletics field”. Replace with the name of the largest school area type in your region.

  • largeLandUseArea: this defaults to “Bontebok National Park”. Replace with the name of a large landuse polygon in your region.

  • srtmFileName: this defaults to srtm_41_19.tif. Replace this with the filename of your SRTM DEM file.

  • localCRS: this defaults to WGS 84 / UTM 34S. You should replace this with the correct CRS for your region.