142

MODULE 10.

OFFICESRUVEY™: IMAGE MATCHING AND ORTHO PROJECTION

Learning Outcomes:

Students should be able to match an imported images with the point cloud and create

ortho-image from point clouds or meshes with RWS.

Lecture Contents:

10.1 Image Matching

When the Preferences in PointScape is set to take a picture automatically before

scanning, the image is automatically matched and hence there is no need for image matching in

RWS except for coloring purpose. If, however, the position of the camera is unknown for an

image, RWS allows the users to import an image and match it with the point cloud. The

matching process requires four pairs of markers, each consisting of a point on the image and one

in the point cloud. After the image is matched, the point cloud can be colored with the color of

the image. Here are the steps

1. From the File menu, select Import Image.

143

2. The Import Image dialog box is open. Navigate the file system to find the image to be

imported and click Import.

3. The image is imported and listed in the List window (Image0002b). Turn the image on

by clicking the light bulb next to it. The image is displayed at the upper left corner of

the 3D View window.

144

4. Select the image by clicking it in the List window and then select Image Matching Tool

from the OfficeSurvey menu.

5. The Image Matching tool dialog box is open. Select an image if there is more than one in

Step 1-Select Image of the dialog box. The two icons next to the dropdown arrow can be

used to hide and maximize/minimize the image.

145

6. Click the Add Point Markers icon in Step 2-Select Matching Markers of the dialog box.

The cursor becomes a + with a number in the 3D View window.

7. Click a point in the image and then a corresponding point in the point cloud. This is the

first pair of markers. Repeat this for the other three pairs.

146

8. Click Preview in the dialog box to see the matching result.

9. Click Coloring in the dialog box to color the point cloud with the matched image color.

147

10. Click Apply to save the matching results and Close to exit the Image Matching tool

dialog box.

148

10.2 Creating Ortho-Images from Point Clouds or Meshes (Surfaces)

Since point clouds and meshes are 3D entities, creating ortho-images from them is a

much more straight-forward process than the traditional method of creating ortho-photos in

which a 2D photograph must be rectified. The Ortho-projection tools in RWS allow users to

project a point cloud or mesh on any plane to produce an ortho-image. Here are the steps.

1. Select a point cloud or mesh. From the OfficeSurvey menu, click Ortho-Projection Tool.

149

2. The Ortho-Projection tool dialog box appears. (Notice that the Segmentation and

Sampling tools are grayed out since the selected entity is a mesh. If it is a point cloud,

then those tools will become available.)

3. In the Orthographic View dropdown list. Select a desired view (Top View in this case).

150

4. Click on the Define Projection Plane by Screen View button in Step 1 of the dialog box.

5. Click the Draw button in Step 2 of the dialog box. A drawing grid appears in the 3D

View window. Click the mouse at the upper left corner, drag the mouse to the lower

right corner and then click it to define a zone for projection.

151

6. Click the Resolution button in Step 3 of the dialog box to adjust the image resolution.

7. Click the Preview button in Step 3 of the dialog box. The ortho-image appears in the 3D

View window.

152

8. Click the Create button. The ortho-image is created and listed in the list window.

9. Click Close to exit the Ortho-Projection tool dialog box. Double-click the name of the

image in the List window to see it.

153

Questions:

1. List the steps to match an image with point cloud.

2. What is an ortho-image? List two methods to define a plane for ortho-projection.

What are the entities that can be used for ortho-projection in RWS? Do you think

that the ortho-images from point cloud have the potential of replacing the ortho-

photos from traditional photogrammetry?