The goal of Lab 7 is to develop skills dealing with aerial photographs and satellite images. This lab focuses on the mathematics involved with these methods. We will look at how to find scales, perimeters, and measurements of certain while using computer images and Imagine satellite images.
Methods
Part 1
In part 1 of the lab we are given multiple images of the map and select distances or elevation on the image. The first image we were given was of a section of an Eau Claire Highway, this length in the real world was 8822.47 feet and on the image it was 3.05 inches. After dividing the actual distance by the image distance I found that the scale was 1:2900.
The second image of part one we were given the focal length from the camera used, 152mm, the elevation of the plane, 20,000ft, and lastly, the elevation of Eau Claire County, 796ft. With this data we had to find the scale of the photo. Which using the formula Scale = (focal length)/(Elevation-Ground level) I found the image was 1:38,400
The third image we used Erdas Imagine and basically plotted points around a lagoon to figure out what the distance around and how much area the lagoon took up. In order to access this tool we used the Measure tool and then selected point, polygon. Next we began placing points around the lagoon until we were all the way around it. We found that the lagoon had an area of 37.7382 hectares or 93.25 acres, and had a perimeter of 4122.28 meters, or just over 2.5 miles.
The last image we were given for this section was a zoomed in image of west south east Eau Claire. For this image we had to find the relief displacement of the smoke stack on the University of Wisconsin- Eau Claire Upper Campus. Using the equation d = (h x r) / (H). where d = relief displacement, h = real world height of object, r = radial distance of top of displaced object from principal point, and H = height of camera above local datum. While since we did not know the actual height of the object we had to modify the formula to h = (d x H)/(r). h = (.5in/3209ft)/(11.4in) after doing the math I found the tower was 140.75 feet.
Part 2
For part 2 we are going to create a terrain looking image. using the stereoscopy images of Eau Claire, ec_city.img and ec_dem2.img which is a digital elevation model of the city. We then used the terrain-anaglyph tool. Inputting the images were the DEM image is under input DEM and the city image is the other input. Then saving the image to our own photos and using 3D (red and blue lens ones) you can see the elevation changes.
 |
| Zoomed in portion of 3D looking image |
This final part of the lab is broken up into many sections. An overall look at what we will be doing in this section is we will be taking two photos and using orthorectification to correct for displacement and what the elevation is.
The first section is to create a new project. we will be using SPOT satellite images of Palm Springs, California. The next step to do is create a new Sat_Ortho block file in our output folders. When going through all the settings make sure to pick UTM in the projection type, Clarke 1866 in the spheroid name, NAD27(CONUS) in the datum name, UTM zone 11, and lastly select north.
The second section is to add imagery to the Block and define sensor model. Here we will be adding frames such as the spot_pan.img. After bringing in the frame click show and edit frame properties. This will then change the Int. tab to green.
The third section is to activate point measurement tool and collect the ground control points. This section will consist of creating ground control points. In this section we will bring in another image to use as a reference image. This step we will create 9 ground control points using the method of selecting the same parts of the image. The next two points will use a different image to collect the points. After adding all the ground control points we will reset the vertical reference source. Here we will use the palm_springs_dem.img. This process will add the vertical z reference to all our points.
Now we will do the same updating to the other image. Because not all the points are on the image we will only have to do a few ground control points.
The next section will be automatic tie point collection, triangulation and ortho re-sample. Here we will use the automatic tie point generation properties icon. After clicking the icon make sure the all available button is activated as well as the exterior button. Then select the distribution tab and change the intended number of points to 40. Lastly we will make sure all the ground point type and standard deviation defaults are changed to 10.
Lastly we will conduct an Ortho resampling. this will basically combine the two images using all the ground control points and tie points. Finally the images are ready to be viewed and after the long process the images have an almost seamless combination.
No comments:
Post a Comment