- Click File | Import (File | Load Data in Voxler 2).
- When the Import dialog opens, navigate to the image.
- Select the image and click Open.
- The georeferenced image will appear in the Network Manager.
Voxler 1 does not support the GeoTIFF format or other georeferenced image files. However, you can use Voxler's Transform module to georeference an image.
Most software products that export georefrenced images have the option to save an associated world file . World files are plain-text files that have a three-letter file extension that is 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. It has the following structure:
Line 1: A, pixel size in the x-direction in map units/pixel
Line 2: D: rotation about y-axis
Line 3: B: rotation about x-axis
Line 4: E: pixel size in the y-direction in map units, almost always negative
Line 5: C: x-coordinate of the center of the upper left pixel
Line 6: F: 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 and choose Properties. In the Summary tab click the Advanced button and make a note of the Height in pixels.
- In Voxler, use File | Load Data to import the image file as a Data module.
- Right click on the module and choose Computational | Transform to add a Transform module to the data.
- Select the Transform module and in the Property Manager and use the following formulae to calculate the Coordinate Limitsparameters:
X = Line 1
Y = The absolute value of line 4
X = Line 5
Y = Line 6 - height in pixels * the absolute value of line 4
- Right click the Transform module and choose 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 (height) location is not possible for all points of the image. You may want to place the image at the median surface elevation of all known points in the image. You can place above or below as the need arises.
Here is an example from a GeoTIFF of a small area in Washington DC. The coordinates are in UTM meters.
The width of this GeoTIFF image is 300 pixels. The height is 180. Below are the lines from the [.TFW] world file
X scale = 1.66666700370338
Y scale = 1.66666661111328
X translation = 323849.999949444
Y translation = 323849.999949444 - 180 * 1.66666661111328 = 323550
Updated October 10, 2016