This question doesn't relate to FWTools functionality, but this seemed like the best place to ask a question like this. I am using gdal to get some of the image info...<br><br>I have a case where I have an image shot from an airplane. I have the below info:
<br><br>height of plane = 1221 meters<br>focal length = 24mm (digital camera, so ~36mm film)<br>EXIF value for X and Y Resolution is 240 (inches)<br>The image dimensions are 2592 x 3872 pixels<br><br>I am trying to calculate the approximate dimensions of this image in ground units (meters).
<br><br>I believe that I can calculate the scale of the image by:<br><br>focal length in mm / 1000 mm per meter/ altitude in meters or<br><br>36 / 1000 / 1221 = 0.036 / 1221 = 0.000029484 <br><br>If the resolution of the image is 240 px per inch, I should be able to calculate an image size in meters:
<br><br>image height= 2592px / 240 px per inch / 39.37 inches per meter = .274321 meters<br><br>image width= 3872px / 240 px per inch / 39.37 inches per meter = .409787 meters<br><br>So using the scale value, I should be able to calculate meters on the ground by taking:
<br><br>.274321 meters / 0.000029484 = 9304 meters<br><br>width on ground = .409787 meters / 0.000029484 = 13898 meters<br>
<br>When I look at the same image that I have georeferenced in a GIS, the image measures about 1000m x 685m. <br><br>I am sure that I am totally screwing this up, and may even be in a case of can't-get-there-from-here. I would appreciate any input that anyone has.
<br><br>I fully understand all of the limitations to this methodology, I am trying for something that is quick, dirty, and automated. I have a bearing and will be doing rotation later, I just first want to get the ground units correct.
<br><br>Thanks, <br><br>David.<br>