Measurement tools can be used to record and export measurements with georeferenced images. This exercise uses the Adobe Photoshop Ruler tool in combination with the Geographic Imager Ruler tab located in the panel.
1.In Adobe Photoshop, choose File > Open and browse to the Landsat 7 Multispectral folder and open Band 8 (Panchromatic), 15 meters.tif.
This is an image of downtown Toronto. The projected coordinate system is NAD 83 UTM Zone 17N in meters. The Geographic Imager panel displays the pixel size. A precise measurement is dependent on the pixel size. For this example, 1 pixel is equal to 15 x 15 meters and provides a moderately accurate measurement.
Non-square pixels prevent the recording of correct measurements when using measurement tools. This can be rectified by using the Geographic Imager Transform function and changing the Pixel Options to keep pixels square.
2.On the Adobe Photoshop Tools panel, click the Ruler Tool button. (If it isn’t visible, click and hold the Eyedropper Tool button to display the flyout menu, then choose the Ruler Tool).
3.Click and drag the Ruler tool anywhere on the map. Release to complete the measurement. A measurement line is drawn on the image.
4.On the Geographic Imager Ruler panel click the Update button.
The measurement is shown in page (pixels) and cartesian units (meters) for Segment L1. Your results may vary depending on how long of a ruler line you drew. Next you’ll use the Ruler Tool to measure another segment.
5.Click the Ruler Tool again. Hold the Alt (Windows) or Option (Mac) key and hover over the end of the first segment. The icon changes to signify that an additional angled segment can be drawn. Click and draw a measurement that is 90-degrees west of the first segment.
6.On the Geographic Imager Rule panel, click the Update button again.
A second segment value is updated in the panel. However, this does not record or save your measured distance. For the above example, the distance recorded is approximately 4,211 meters. Your results may vary depending on how long of a ruler line you drew. The measurements can be saved to the clipboard.
7.At the bottom-right of the Ruler tab, click the Copy to Clipboard button.
8.On your desktop, create a new text document and paste the measurements into it. Rename the output file to measurements.txt and save it.
Remember the resolution of the image will reflect how accurate the measurements will be. Measurement tools can not be used with non-square pixels because each side has a different length.
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