GSP 216: Introduction to Remote Sensing

Name:______

Lab 4 - Photogrammetry

Introduction

Photogrammetry is process of making measurements from photographs. In this lab we will become familiar with the basicphotogrammic techniques. We will use digital aerial photographs to take measurements and calculate scale, distance and areas of features in the photographs.

Learning Outcomes

  • Identify basic components of aerial photographs.
  • Calculate the actual size of objects based on measurement made on aerial photographs.
  • Calculate the approximate scale of an aerial photograph using a feature of a known size.
  • Calculate distances and areas of features based on measurement made on aerial photographs.
  • Calculate the height of objects using the relief displacement method and the shadow method

In today’s lab we will be using digital aerial photos to take our measurements. We will use GIMP(GNU Image Manipulation Program) to open up various aerial photos and take measurements using the “measure” tool. GIMP is a free, open-source image editing software available for download.

  1. On your local computer under your GSP 216 folder create a sub-folder named “Lab_04”.
  1. Download the data. Locate your Lab_04 Folder and copy and paste the ZIP file into your folder.
  1. Right click on the file “Lab04_Photos.zip” and select “Extract All”. Now the files have been uncompressed and are ready to view.
  1. Open up GIMP program (it may take a while for it to start up the first time). Navigate to the “Tools” menu and select the “Measure” tool. You are now ready to start the rest of the lab. You can change the measurements units of the tool on the bottom left hand corner of the screen.
  1. Open up “Arcata1.tif” in GIMP. Look at the aerial photograph of the Arcata areaand answer the following questions:

Identify the elements marked on the photo:

A.______

B.______

C.______

  1. When was the photo acquired?
  1. Open up “HumboldtBay1.tif” and “HumboldtBay2.tif” in GIMP and answer the following two questions;

What film type was used for these aerial photos?

  1. What is the direction of the flight path in these two photos? (You may want to look at the Principal Point(PP) and Conjugate Principal Point (CPP) and Frame numbers)

Photo Scale

S = Photo Scale =

  1. Open up “Humboldt1956.tif” in GIMP. The scale of this photo is 1:30,000.
  2. Use the measure tool in GIMP to estimate the length of the runway (in meters) indicated on the photo. Show your calculations.
  1. If the measurement you made on the aerial photo were to changes by 0.1 mm, how much would your estimate of the runway length change?
  1. Open up “Seattle.tif” in GIMP. Identify a feature in the photo that has a known length, indicate which feature you chose in your answer. Use this feature to calculate the scale of the photo.
  1. Using the scale you calculated in the previous questions, what is the diameter of the halo (the widest part) of the Space Needle in feet?
  1. Now research the actual diameter of the Space Needle, what is it and how close was your estimate? What are some factors that impact the accuracy of your estimate?
  1. Open up “WashingtonDC.tif” image in GIMP. The scale of this photograph is 1:12,000. Use the measure tool to determine the total area of the reflecting pool in both square feet and in acres.

Object Height Based on Shadow Length

H = L x tan ()

H = Height of object

L = Length of the shadow

 = Solar elevation (altitude) angle

  1. Using the same image (“WashingtonDC.tif”) determine the height of the Washington Monument. We know the following information about the photograph: Scale is 1:12,000 and the photo was taken on April 5, 1988 at 11:30 AM. You will need to use the NOAA Solar Calculator ( to determine the solar elevation (or altitude) on this day in Washington D.C.

S = Scale

f = the focal length of the camera

H = the flying height above sea level

h = the average elevation of the terrain above sea level

  1. Open up “SuperiorWI.tif” image in GIMP. In this aerial photo the flying height was not provided, but we know the scale and the average elevation of the region in the photograph. The scale is 1:26,065 and the average elevation of the region is 187m and the focal length of the camera is 152.03 mm. Calculate flying height in metersusing this information.

Object Height Based on Relief Displacement

d = length of displaced object on the photo

r = radial distance from principal point to displaced image point (top of building)on the photo

ho = height of the object

H’ = flying height above the surface (H-h)

  1. Calculate the height of the grain terminal (in meter) indicated in the photo using the relief displacement method. Use the flying height (H) and the elevation above sea level (h) from question10to determine H’.