- Click File | Import.
- In the Import dialog, select the image and click Open.
The georeferenced image will appear in the Network Manager.
Most software products that export georeferenced images have the option to save an associated world file. World files are plain-text files that have a three-letter file extension that contain the first and last letter of the image file's extension, followed by the letter "w". For example:
You can open the world file in a text editor like Notepad to see the structure:
Line 1: pixel size in the x-direction in map units/pixel
Line 2: rotation about y-axis
Line 3: rotation about x-axis
Line 4: pixel size in the y-direction in map units (almost always negative)
Line 5: x-coordinate of the center of the upper left pixel
Line 6: y-coordinate of the center of the upper left pixel
Using this information and the following procedure you can georeference an image:
- Open the world file in a text editor.
- Right click on the image file in a Windows Explorer window and click Properties.
- In the Details tab make a note of the Height. This value will be in pixels.
- Using the information from the world file and the Height from the the image, calculate the following:
X = Line 1
Y = abs(Line 4)
X = Line 5
Y = Line 6 - Height * abs(Line 4)
- In Voxler, use the File | Import command to import the image file as a data module.
- Right click on the data module in the Network Manager and click Computational | Transform.
- Select the Transform module in the Network Manager.
- In the Property Manager, on the Transform page, enter the values from step 4 into the X and Y fields in the Scale and Translation sections.
- Right click the Transform module in the Network Manager and click Graphics Output | OrthoImage.
This will display your image in the correct X and Y coordinates of the image's coordinate system. Raster images are flat by definition, so choosing a correct Z (depth or elevation) location is not possible for all points of the image. You may want to place the image at the median surface elevation or depth of all known points in the image.
Here is an example from a GeoTIFF of a small area near Denver, CO (Denver.tif). The coordinates are in UTM meters, and the height is 697 pixels. Below are the lines from the Denver.tfw world file.
X scale = 519.058083896737
Y scale = 518.994026116067
X translation = 172045.09621213
Y translation = 4538752.53701579 - 697 * 518.994026116067 = 4177013.700812891
Updated July 17, 2018