BELAJAR QGIS - Part 2: Georeferencing dan Proyeksi

Introduction

In this tutorial, we will learn how to georeference raster data that lacks spatial references and convert its coordinate system from geographic to UTM using QGIS. This guide is designed for users of all levels who want to enhance their skills in Geographic Information Systems (GIS) with QGIS.

Step 1: Understanding Georeferencing

• What is Georeferencing?

  • Georeferencing is the process of aligning spatial data (like images) to a coordinate system so it can be viewed and analyzed with other spatial data.

• Why Georeference?

  • It allows you to integrate raster data with other spatial datasets, enabling more robust analysis and visualization.

Step 2: Preparing Your Raster Data

• Select Your Raster Data

  • Start with a raster image that does not have a spatial reference.

• Open QGIS

  • Launch the QGIS application on your computer.

• Load Your Raster Data

  • Go to the "Layer" menu.
  • Select "Add Layer" > "Add Raster Layer."
  • Browse and select your raster file.

Step 3: Adding Control Points

• Open the Georeferencer Tool

  • Navigate to "Raster" > "Georeferencer" > "Georeferencer."

• Set Up the Georeferencer

  • In the Georeferencer window, load your raster by selecting "File" > "Open Raster."

• Add Control Points

  • Use the "Add Point" tool to click on known locations in your raster image.
  • Match these points with their corresponding coordinates on a reference layer (e.g., a basemap).
  • Repeat this step for at least four points distributed across the image for accuracy.

Step 4: Settings for Transformation

• Select the Transformation Type

  • In the Georeferencer toolbar, click on "Settings" > "Transformation Settings."
  • Choose a transformation type (e.g., Linear, Helmert, etc.) based on the level of accuracy required.

• Specify Output Options

  • Set the output raster file format and destination folder.
  • Choose a target Coordinate Reference System (CRS), preferably the one you intend to use (e.g., UTM).

Step 5: Running the Georeferencing Process

• Start Georeferencing

  • Click on the "Start Georeferencing" button in the Georeferencer window.
  • Monitor the process and check for any errors.

• Check the Result

  • Once completed, load the newly georeferenced raster into your QGIS project to ensure it aligns correctly with other spatial data.

Step 6: Changing the Coordinate System

• Open the Raster Layer Properties

  • Right-click on the georeferenced raster layer in the Layers panel.
  • Select "Properties."

• Transform the CRS

  • Go to the "Source" tab.
  • Click on "Set CRS" and choose the desired UTM zone for your data.

• Export the Layer

  • Right-click on the layer again, select "Export" > "Save As."
  • Choose the format, specify the location, and ensure you select the correct CRS before saving.

Conclusion

In this tutorial, we covered the essential steps to georeference raster data and change its coordinate system in QGIS. By following these steps, you can effectively integrate and analyze various types of spatial data. For further learning, experiment with different raster datasets and explore additional QGIS functionalities to enhance your GIS skills.