Installing Gif Image in Your Overlay

  1. Copy your .gif file to the overlay directory.
  2. Create a new layer called Underlay using the Add/Delete menu.
  3. Go back to the Options menu to turn on the new Underlay layer, so you can see it later.
  4. In the Add/Delete menu:
    1. Select Add underlay
    2. Select Underlay layer, then
    3. Fill in the underlay properties box.

      The projection type is Equidist Cylinder.

      The center and projection reference should be the center of your image.

    4. Sometimes the downloaded image seems to be 1° or 1 minute off from the expected value. To compute the underlay scale, first compute the range scale, which is the number of km/degree at your center latitude, with the following equation:
      R a n g e S c a l e = π 180 × 6371 k m × cos ⁡ ( L a t i t u d e )
    5. Divide by the GIF scale (in pixels/degree) to give you the underlay scale in km/pixel.

      For example, an overlay centered at 45° north, has a range scale of 78.62 km/degree (48.9 mi/degree), and at 120 pixels/degree, yields 0.65522 km/pixel (0.4 mi/pixel).

  5. Apply and save.