Open Images and Transform Tutorial

Open Images

Opening a spatial image is similar to opening up any other image in Adobe Photoshop.

1.Make sure you have installed Geographic Imager.

2.In Adobe Photoshop, choose File > Open. Browse to the \Tutorial Data\Americas folder and open both Americas_1.tif and Americas_4.tif.

Make the Americas_4.tif file the active document and open the Geographic Imager panel. If the panel is not visible, choose Plugins > Avenza Geographic Imager > Geographic Imager.

The Americas_4.tif has no spatial data, however, you can specify reference information and a coordinate system using the Geographic Imager panel.

A reference file contains coordinates that describe the location, image size, pixel size, and rotation of an image file. It does not contain actual image data. Next, you'll specify a reference file for the Americas_4 document.

3.With the Americas_4.tif file as the active document, click the Reference file Specify link in the Geographic Imager panel.

4.Select Americas_4_reference.tfw and click Open.

The reference file Americas_4_reference.tfw (World reference file) is listed in the Geographic Imager panel. On the General and Corners panels, spatial information is displayed as well, including image extents, pixel size and top-left and bottom-right coordinates.

The next step is to provide a coordinate system for the image.

5.Keep these images open for the next tutorial.

Specify a Coordinate System

Some reference files do not store coordinate system information. For example, the previously used tfw world file does not contain any coordinate system. To continue the tutorial, you need to specify a source coordinate system. For more information on reference files, see Specifying a Reference File.

The Americas_4.tif currently has no coordinate system assigned. You’ll specify a coordinate system similar to the Americas_1.tif using these steps.

1.With the Americas_4.tif file still the active document, click the Coordinate System Specify link in the Geographic Imager panel.

You can specify a coordinate system for the active document in one of two ways: choosing from a database of coordinate systems or choosing one that another open image has. First, choose from a database of coordinate systems:

2.In the Specify Coordinate System dialog box, click the [No Coordinate System Specified] link.

3.In the Select Coordinate System dialog box, expand the Coordinate Systems > Geodetic > World category, select WGS 84 in the coordinate system list and click OK.

4.Click OK in the Specify Coordinate System dialog box.

Alternatively, you could use the Same as option since Americas_1.tif also has a WGS 84 coordinate system.

This assigns the WGS 84 coordinate system to the Americas_4.tif document. The information is updated on the Geographic Imager panel.

5.Keep these documents open for the next tutorial.

Transform a Coordinate System

Transforming a coordinate system transforms a georeferenced source image into a destination georeferenced image with a different coordinate system. In this exercise, the image will be transformed from WGS 84 coordinate system to Lambert Conformal Conic coordinate system.

1.With Americas_4.tif still the active document, click the Transform button on the Geographic Imager panel.

2.In the Transform dialog box, click the WGS 84 link to select a different destination coordinate system.

This is different than specifying a source coordinate system. A destination coordinate system is the coordinate system of the image after it is transformed.

3.Expand the Coordinate Systems > Projected > North America > United States category, select United States: Lambert Conformal Conic, meter from the coordinate system list and click OK.

This sets the destination coordinate system that will be used for the transformation. At this point, Geographic Imager automatically selects an appropriate datum shift to be performed during the transformation process. If this datum shift needs to be changed, click the Datum shift hyperlink to open the Specify Datum Shift dialog box and select the desired datum. See page Geographic Imager user guide for an explanation of datum shift.

 Note that the Pixel Size is 7077.28950515 meters. The pixel size can be changed to any user specified value. This essentially changes the size of the image as each pixel represents a geographic unit. In this instance, we will leave the pixel size as the default.

4.Click the Transform button.

The image is transformed to a Lambert Conformal Conic projected coordinate system.

5.Make the Americas_1.tif file the active document and click the Transform button on the Geographic Imager panel.

The panel displays the coordinate system as WGS84. You’ll also transform it to the Lambert Conformal Conic projected coordinate system.

6.Click the Same As check box and choose Americas_4.tif (United States: Lambert Conformal Conic, meter) from the drop-down list.

7.Click Match the pixel size when prompted.

8.Click the Transform button.

Both images are now in the same projected coordinate system (United States: Lambert Conformal Conic, meter) and have the same pixel size. From here, the images could be mosaicked together or saved to retain referencing.

 

Want to follow along to this tutorial?

Please see our corresponding YouTube videos for the various Geographic Imager tutorials covered in our online documentation!*

* Providing a general overview of the steps covered in this tutorial, our Open Images and Transform video tutorial will walk you through the importing and transformation process in Geographic Imager.