Orthorectifying images and true orthorectification

Before you orthorectify your images, you must ensure that in the Set Projection window the value of Output pixel spacing is set correctly. It is this value that determines the resolution of the orthorectified images.

By default, the channel type for your orthorectified images is the same as your input channel.

To set up orthorectification

In the Ortho Image Production window, in the Available images list, click one or more images to process, and then to move the image or images to the Images to process list, click Move Selection.
To move all the images, click Move All.

The images are processed in the order in which they appear in the Images to process list. If you have already orthorectified the image, Delete existing file appears next to the image. When the image is orthorectified, the previous version is replaced. If you have not orthorectified the image previously, Create new file appears.
Under Images to process, click an image.
Under Uncorrected Image, click All to select all the image channels, or click Channels, and then type the channels that you want in the Channels box.
To specify a range, type a dash (-) between the channel numbers (for example, 1-3). To specify individual channels, separate each with a comma (1,3).
Repeat the previous step for each remaining image, or to use the same channel selection for the remaining images, select the Apply input channel selection to all files check box.
Under Ortho Image, in the File box, type a new file name for the orthorectified image, or click Browse to select a file (or folder: see the following note).
The default file name is O followed by the file name of the raw image; for example, O129.pix. If you replace the default file name with the file name of an existing file with matching georeferencing and resolution, the new orthorectified image will replace the old one. If the georeferencing and resolution of the existing file do not match the new orthorectified image, you must give the file a new name.

Note: When you have two or more files selected under Images to process, the Browse For Folder dialog box appears, in which you can selct a folder for the selection. When you have only one file selected, the File Selector dialog appears.
If necessary, you click the Recompute button to reset Upper left and Lower right to the default values, which represent the computed footprint of the image on the ground.
The Upper left and Lower right values may be defaults or the extents from an existing orthorectified image. If the computed bounds appear too large or too small, it may indicate errors in the math model or the digital elevation model (DEM).
To select the format to use for the output, in the Format list, click PCIDSK (.pix) or TIFF (.tif), as applicable.
To select file-creation options to apply to the output file, click Options. When you are finished, click OK in the GDB Options Editor window.
Note: Different options are available for different file types. For a complete list of GDB-recognized file types, including the options available for each, see About Generic Database file formats
In the Output NoData box, type a background (NoData) value to use for ortho pixels that are not populated.
All channels are set to the same background value. The specified background value will be truncated to the range allowed by the source-image data type.
In the Automatic edge clip box, type or select a number to represent the percentage of the raw input image that you want to remove.
For example, to remove 5 percent of the width from the left and right edges, and 5 percent of the height from the top and bottom edges of the raw input image, enter 5.

Rather than having the clpping applied to the raw input image, to clip the orthorecitifed output image, enter a negative value.

If a clip region is specified, the edge clip value specified will be applied to the contents of the clipped region.
To use the same format options for all of your images, select the Apply format options to all images check box.
Note: After you select this check box, the format options are set for all of the images. Clearing the check box does not clear the format options set for any of the images. You must reset these options separately for each image.
Under Elevation Information, do one of the following:
- Click Constant height, and then in the box to the right, type an elevation value.
  
  This value will be used as the constant elevation value to correct all pixels in your image(s). For example, if you want to use a constant elevation of zero to correct your image(s), type 0.00 in this box.
- Click DEM file, and then do the following:
  1. Click Browse, in the File Selector window, select the DEM you want, and then click Open.
  2. Click DEM Settings.
  3. In the DEM File window, follow the steps outlined in Setting DEM file options.
To use the same Elevation Information options for all your images, select the Apply DEM options to all images check box.
Note: After you select this check box, the DEM options are set for all of the images. Clearing the check mark does not clear the DEM options set for any of the images. You must reset the DEM options separately for each image.
Under Processing Options, in the Sampling interval box, type or select the interval between the pixels to use to process the image.
Be sure to set the interval correctly, especially in rugged areas. Setting it too high will reduce the detail of the terrain correction.
In the Resampling list, click the processing method you want to use.
If you selected 8 Pt Sin X/X or 16 Pt Sin X/X from the Resampling list, click an appropriate option in the Shaping window list.
Note: The shaping window specifies a window that attenuates the SINC coefficients to reduce resampling artifacts.

The following shaping window options are available:
- NONE: generates resampling artifacts
- KAISER: generates good visual results and reduces resampling artifacts
- HANN: generates acceptable visual results like KAISER, but without the extra control afforded by the BETA value
- HAMMING: similar to HANN, but produces more resampling artifacts, as it does not fully attenuate the SINC function to 0 at the edge of the window
- LANCZOS: generates good visual results, especially for edge preservation, but can cause some ringing and other resampling artifacts
- PARABOLA: generates a few blocking artifacts, but not as many as NONE. This value is the default.
If you selected KAISER in the Shaping window list, type a value between 1.0 and 10.0 in the BETA box. This value determines the shape of the KAISER window. A higher BETA value produces greater attenuation of the SINC coefficients.
If in the Resampling list you selected Average filter or Median filter, you can specify a filter size in the boxes beside Filter size.
To set the size of the kernel to use with the filter: in the X box, type the number of pixels in width, and then in the Y box, type the number of pixels in length.
If you want to perform true orthorectification on the images, under True Orthorectification Information, select the Apply true orthorectification check box, and then do the following:
- In the Building model file box, type the path and file name of the building model file to use, or click Browse to select a file.
  After you select the file, the Settings window appears, in which you specify settings for each available layer. For more information on using this window, see Setting true-orthorectification options. At any time you want to review or change the settings, click Settings.
Under Processing Start Time, do one of the following:
- To begin the orthorectification process immediately (on clicking Generate Orthos), click Start now.
- To begin the orthorectification process at a specific time, click Start at (hh:mm).
  - In the boxes below, type or select the hour and minute at which to start, and then click a.m. or p.m., according to the time you want (within 24 hours).
Click Generate Orthos.

For more information, see: