The size of the orthophoto to be generated is established using the Output Image Size or Scale settings.
Orthophotos are often used as a form of scale drawing. In that situation, you need to be able to export an image that has a defined scale relationship with the real object being modeled in PhotoModeler.
Note: if you wish the orthophotos to have an accurate scale, you should add a Scale to your project first unless it was done with Control Points. See Importing and Setting Up Coordinate Systems.
There are four ways of defining the output image size and the scale. The first is the simplest; you enter the percentage of the Input Pixel Size Average, where the Input Pixel Size Average is shown in the section below.
Or, second, you enter in the number of horizontal and vertical pixels in the output. This provides an image of known size but of unknown scale.
The third is to define the image scale in terms of pixels per unit. For example, you might want the exported orthophoto to have 20 pixels for every foot on the real object (defined in the mapping plane by orthographic projection). That way you could measure pixels in the image and get true dimensions (10 pixels in the image would 0.5 feet on the object in this example). The inverse can be defined too (i.e. units per pixel).
The fourth is to define the image scale in terms of the print scale. This is used when you are printing the image and want the printed result to be a scaled drawing. First you define the scale you want (e.g. 1 to 10), then you define the pixels-per-inch (ppi) or pixels-per-mm (ppm) that the image will be printed at (note that you might need to use an external program like Photoshop to change the image dots-per-inch and then have it print it). There are many rules for picking an appropriate number of pixels per unit but as a rule if you are printing to a 600 dots-per-inch black and white laser printer, and you want reasonable grayscale rendition you should not use much higher than 100 pixels-per-inch.
Below the size settings is information about the output image and the input imagery. The output resolution in pixels, the size in memory (in MB, which may differ from size on disk if the image is compressed), and the output pixel size are calculated based on the image size settings above.
The input photo pixel sizes (range and average) are calculated when the dialog opens based on the 3D points in the project and the images they’re marked on. Because the surface is unlikely to be perfectly flat (and the camera that took the photos is likely not at the exact height for all points), the pixel size will vary - so the range and average are calculated. These are useful values when you want the exported orthophoto to match the input photo resolution. For example, in the screen shot shown above, the Image Scale is set to 0.00697 inches per pixel to match the smallest input image pixel size.
Note: The size of the output image (in terms of resolution, size in MB, and output pixel size) is updated when you click the Update button as these values will vary depending on the settings above. Be aware of the output image size so that the image exported is not too large which can cause image processing delays.