Mastering QGIS
上QQ阅读APP看书，第一时间看更新
上一章目录下一章

Importing data into a SpatiaLite database

Importing data into a SpatiaLite database is easy using the DB Manager. SpatiaLite supports the following formats for importing files:

  • Shapefile (.shp)
  • Dbase (.dbf)
  • Text (.txt), Commas Separate Values (.csv), and Excel spreadsheets (.xls)
  • Well-known Text (.wkt) and Well-known Binary (.wkb)
  • PostGIS (.ewkt / .ewkb)
  • Geography Markup Language (.gml)
  • Keyhole Markup Language (.kml)
  • Geometry JavaScript Object Notation (.geojson)
  • Scalable Vector Graphics (.svg)

Let's use DB Manager to import data in a few different formats into our GiffordPinochet.sqlite database.

Importing KML into SpatiaLite

To import a KML file into a SpatiaLite database, complete the following steps:

  1. Open DB Manager by clicking on DB Manager under Database. Expand SpatiaLite and select GiffordPinochet.sqlite on the Tree panel.
  2. Navigate to Table | Import layer/file to open the Import vector layer dialog.
  3. Click on the ellipsis button at the right-hand side of the Input drop-down box and select and open streams.kml from the sample dataset that is available for download on the Packt Publishing website.
  4. Click on the Update options button to load the remainder of the dialog box. The output table name will populate as streams, and it will match the base name of the input file.
  5. Set the following options as shown in the next screenshot:
    • Select Source SRID and enter 4326. This is the EPSG code for all KML datasets.
    • Select Target SRID and enter 26910. This is the EPSG code for NAD 83/UTM Zone 10 North.
    • Select Create spatial index.
  6. Refer the following screenshot to make sure your settings match. If so, click on the OK button to import the file.

    Note

    By setting the target SRID to a different value than the source SRID, the data will be projected to the new coordinate system during the import process, saving you a step.

    Importing KML into SpatiaLite
  7. After a few moments, you will be notified that the import is complete. To view the newly created table, you'll need to refresh the Tree panel by selecting GiffordPinochet.sqlite in the tree and then click on Refresh under Database, or press the F5 key on your keyboard. The streams table should now appear and have the polyline icon next to it.
  8. To preview the attribute table, click on the Table tab on the information panel. To preview the geometry, click on the Preview tab on the information panel. To view the newly created SpatiaLite layer in QGIS Desktop, right-click on streams on the Tree panel, and then choose Add to canvas.

Importing a shapefile into SpatiaLite

  1. Open DB Manager by clicking on DB Manager under Database. Expand SpatiaLite and select GiffordPinochet.sqlite on the Tree panel.
  2. Navigate to Table | Import layer/file to open the Import vector layer dialog, as shown in the following screenshot.
  3. Click on the ellipsis button at the right-hand side of the Input drop-down box and select and open NF_roads.shp from the sample dataset that is available for download on the Packt Publishing website.
  4. Click on the Update options button to load the remainder of the dialog box. The output table name will populate as NF_roads, and it will match the base name of the input file.
  5. Set the following options:
    • Select Source SRID and enter 26910. This is the EPSG code for NAD 83/UTM Zone 10 North. Since we don't want to change the coordinate system during import, we do not need to set Target SRID.
    • Select Create spatial index.
  6. Click on the OK button to import the file.
    Importing a shapefile into SpatiaLite
  7. After a few moments, you will be notified that the import is complete. To view the newly created table, you'll need to refresh the Tree panel by selecting GiffordPinochet.sqlite in the tree, and then click on Refresh under Database, or press the F5 key on your keyboard. The NF_roads table should now appear and have the polyline icon next to it.
  8. To preview the attribute table, click on the Table tab on the information panel. To preview the geometry, click on the Preview tab on the information panel. To view the newly created SpatiaLite layer in QGIS Desktop, right-click on NF_roads in the tree, and then choose Add to canvas.

Importing tables into SpatiaLite

To import a table file into a SpatiaLite database, complete the following steps:

  1. Open DB Manager by clicking on DB Manager under Database. Expand SpatiaLite and select GiffordPinochet.sqlite on the Tree panel.
  2. Navigate to Table | Import layer/file to open the Import vector layer dialog.
  3. Click on the ellipsis button to the right-hand side of the Input drop-down box and select and open Waterfalls.xls from the sample dataset that is available for download on the Packt Publishing website.
  4. Click on the Update options button to load the remainder of the dialog box. The output table name will populate as Waterfalls, and it match the base name of the input file. Note that all options related to spatial datasets are not modifiable and are grayed out (as shown in in the following screenshot). This is because SpatiaLite treats the input as a nonspatial table, even though it has coordinates stored in the table. We will add the spatial component to the table in a later step.
  5. Click on the OK button to import the file.
    Importing tables into SpatiaLite
  6. After a few moments, you will be notified that the import is complete. To view the newly created table, you'll need to refresh the Tree panel by selecting GiffordPinochet.sqlite in the tree and then click on Refresh under Database, or press the F5 key on your keyboard. The Waterfalls table should now appear and have the table icon next to it.
  7. Select the Waterfalls table. Click on the Info tab on the information panel. Note the Northing and Easting fields. These fields contain the coordinates of the waterfalls in NAD 83/UTM Zone 10 North (EPSG 26910). Click on the Table tab on the information panel to view the entries in the table. Note that the Preview tab is not selectable, because the selected table does not have any geometry field.

At this point, the table import is complete. However, since the Waterfalls table has coordinate pairs, a point geometry column can be added to the table that would essentially convert the table to a point layer. Let's do this now:

  1. With the Waterfalls table selected in the Tree panel, navigate to Table | Edit Table to open the Table properties window.
  2. Click on the Add geometry column button. In the new window, set the following options to match the following screenshot and then click on OK to create the geometry field:
    • Name: geom (the name of the field that will contain the geometry information)
    • Type: POINT (the type of geometry the field will hold)
    • Dimensions: 2 (the number of dimensions (values) the geometry field will hold for each record)
    • SRID: 26910 (the coordinate system of the geometry field)
    Importing tables into SpatiaLite
  3. Close the table properties. To view the newly edited table, you'll need to refresh the Tree panel by selecting GiffordPinochet.sqlite in the tree and then clicking on Refresh under Database, or press the F5 key on your keyboard. The Waterfalls table should now appear and have the point icon next to it.

Now that the Waterfalls table has a geometry field, we need to populate it with the coordinates. We will accomplish this by writing a SQL update query and using the SpatiaLite MakePoint function. To do this, perform the following steps:

  1. In the SQL window, click on the Clear button to clear the SQL query text area.
  2. Enter the following query in the SQL query text area: 
    UPDATE Waterfalls 
SET geom = MakePoint(Easting,Northing,26910);

    Note

    Let's discuss the MakePoint function.

    MakePoint(Easting,Northing,26910) is a SpatiaLite function that creates a new point geometry object. Easting and Northing are the columns in the same row that hold the values for the x and y coordinates respectively. 26910 is the SRID of the x and y coordinates.

  3. Click on the Execute (F5) button to execute the query. The query will return no result but will indicate that 100 rows were affected. This indicates that the geometry field of 100 rows have been populated with point geometry. The following screenshot shows the query and the indication that 100 rows were affected:
    Importing tables into SpatiaLite
  4. On the SQL window, click on the Close button to close the window.
  5. To view the changes made to the Waterfalls table, you'll need to refresh the Tree panel by selecting GiffordPinochet.sqlite in the tree and then clicking on Refresh under Database, or press the F5 key on your keyboard.
  6. Note that the Waterfalls table now has the point icon next to it. Click on the Info tab on the information panel. Under the SpatiaLite section of the information printout, note that a warning is displayed stating that no spatial index has been defined (shown in following figure). To improve access speed, it is best that a spatial index be set. Click on create it and then click on the Yes button on the pop up.
    Importing tables into SpatiaLite
  7. To preview the attribute table, click on the Table tab on the information panel. To preview the geometry, click on the Preview tab on the information panel. To view the newly created SpatiaLite layer in QGIS Desktop, right-click on NF_roads in the tree and then choose Add to canvas.
本周热推：
Python编程：从入门到实践Python编程：从入门到实践（第2版）C Primer Plus（第6版）中文版【最新修订版】区块链架构之美：从比特币、以太坊、超级账本看区块链架构设计Python从入门到精通
上一章目录下一章