When the settings are made, click OK to close the dialog box. Specify the destination coordinate system as WGS84. We will use those latitude and longitude values for the georeferencing. When those latitude and longitude values are collected, those values are collected in the decimal degree format and the values are in degree in WGS84. Click the “Specify” button to find the coordinate system from the coordinate systems list. The image of the coordinate system is WGS84 / Pseudo-Mercator as found in Step 2a. Here we’ll specify the coordinate system. In the Format section, click the blue “Specify” link to open the Input Format dialog box. The Georeference dialog box will open.įirst, we’ll need to set the proper image coordinate system and input coordinate system (the information from Step 2a). In Geographic Imager, click the Georeference tool button ( ) in the Geographic Imager main panel (or choose File > Automate > Geographic Imager: Georeference).
Step 3: Georeference in Geographic Imager The latitude and longitude values are in decimal degree format and the coordinate system of those values is in the geodetic system “WGS84”. The latitude and longitude values are at the centre of the point (cross) symbol after clicking the “add placemark” symbol in the Google Earth window.įind the coordinates of two additional ground control points. Record the collected latitude and longitude values. Place a point symbol to help identify the coordinate values. Using Google Earth, find the exact same spot as the one decided in the non-georeferenced image. For the first point, we’ll use the southeast corner of the runway by the water. It should be available on Google Earth where you’ll find the X, Y coordinate values. On the non-georeferenced image, decide which spot to use as a point of reference. Below are the steps for finding out one of the ground control points. We’ll need to define at least three ground control points for georeferencing. The image, collected from Google Earth, is projected in a coordinate system called WGS84 / Pseudo Mercator (this projection is common to Web-based mapping systems and is also known as Web Mercator or Google projection). In order to transform it to another coordinate system or projection, mosaic with other images, or align the image to vector work using MAPublisher for Adobe Illustrator, the image must first be georeferenced.Īs indicated above, two key pieces of information are required to georeference an image: a) the coordinate system of the image and b) defining ground control points This image is in JPEG format and there is no georeference information associated with it. Now that you know what you’ll need, we’ll demonstrate a georeference workflow using the Geographic Imager Georeference tool and Google Earth. Cultural features such as road intersection, a sharp corner of a lot, or a boundary are good examples of locations used as ground control points. Furthermore, to make georeferencing easier, ground control points must be clearly identifiable in the image. longitude), and 4) Ground Y coordinate (e.g. One ground control point consists of several values: 1) Pixel X coordinate, 2) Pixel Y coordinate, 3) Ground X coordinate (e.g.
The second requirement is working with the ground control points. If you cannot get the information of the coordinate system assigned to the image, you might want to try georeferencing with different coordinate systems to make the map as precise as possible. If you are unsure about which coordinate system the image uses, contact the data provider or search the metadata of the image on the Internet. The first thing you need to know is the coordinate system or projection of the image you are georeferencing. These points are known as ground control points.
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