GEO 4120c Workshop

Air Photo Geometry and Horizontal Measurements

9 February 2009

NOTE: GoogleEarth has measurement capabilities that may remove the need to use topo quads. Find out about accuracy, etc., and change this workshop accordingly.

Introduction

Basic photogrammetry is an important part of air photo interpretation. The sizes of objects on the ground are one of the most important characteristics for their identification, and many applications of aerial photography include measurements of the length and area of various objects.

Sources of Ground Measurements for this Workshop - A local air photo and USGS Topographic Quadrangle

·     UF Map and Imagery Library

·          Florida Land Boundary Information System (LABINS) - gateway to DOQ of Florida
GoogleEarth
Instructor's collection


             Equipment for this exercise:

                Ruler/straightedge
             Protractor
             Aerial Photo with standard marks (from instructor, M&E library, or your own)
             Clear transparency
             Fine-point marking pen for transparency
             Masking tape


Exercise

Choose one of the aerial photos that the instructor has, go check out a more interesting one from the M&E Library, or bring one from home. Be sure that the aerial photo that you select has all the marks of traditional, standard aerial photography

When marking on the overlay, be very neat and create professional-looking results. Make an effort to letter well, start and finish lines evenly, and draw figures (e.g. the compass rose) accurately. I will grade this workshop, and others like it, partially on the basis of how neatly drawn the overlays are.


1. Overlay the photo with a transparency and tape the two together. It is best to tape the photo to the table top, then tape the transparency over the photo.

2.   Identify the fiducial marks and indicate them neatly on the overlay.

        3. Identify the Principal Point and mark it neatly on the overlay.
4. Find the topograpic quadrangle on LABINS or in the M&E Library that covers the site in your air photo, or find the location in GoogleEarth and set it up so you can make measurements. Name the topo quad, its series, its projection characteristics, and its scale in a document. If you use GoogleEarth, state that you did so, e-mail the image to yourself, and include it when you hand in the workshop.

5. Determine the true scale of the air photo and mark it on the overlay. Do this by measuring an object on the photo and the same object on the topo quad or GoogleEarth, and then using the ratio to calculate the true scale. Mark the measured object on the photo overlay.
       a. Assume that your photo was acquired with a camera and lens with a focal length of 6", calculate the height above ground that the airplane was flying. Show your work.
       b. Assume that the height above ground that the airplane was flying was 4,000'. Calculate the focal length of the camera and lens. Show your work.

6. Pick out several (three or four) linear features such as rivers, roads, or railroads and measure their lengths between two interesting points. Indicate the features and their lengths on the overlay.

7. Pick out several features such as lakes, wetlands, or developed areas and measure their areas. Indicate the areas on the overlays.

8. Determine the cardinal directions (N, E, S, W) and mark them on the overlay as a compass rose.

9. Determine the bearing (0-360º) from the one corner of the air photo to another.

10. Finally, pick out a couple of interesting features in your air photo, and measure the bearing (and back bearing) from one to the other.


Turn in to G:\share\student share\GEO 4120c\yourfolder\ or e-mail to Dr. Binford mbinford@geog.ufl.edu

        Write descriptions (question 4) and calculations (5 a and b) in a word processing file or hard copy printout.

Turn in the air photo with taped-on overlay to Dr. Binford at the beginning of the next class. Be sure to put your name on the overlay before you turn it in.