Image Draping

Figure 1: Geologic Image File and Grid/Data Reference

Figure 2: Plan View of Draped Geologic Map

Figure 3: Oblique View (from North) of Draped Geology

From DGInsider Q1 2000/Q4 1999

Have you ever wanted to drape a geologic map over your 3D model? How about an aerial photo or satellite image? Well, EarthVision has the capability to do just that, even if you do not have a set of control points to register the image to a file with a known coordinate system.

First, you need to format your image as an SGI-format .rgb file. You should be able to do this with some photo editing software like Adobe Photoshop (used in conjunction with DeBabelizer from Equilibrium), Image Alchemy from Handmade Software, or Imgworks (if you are using an SGI). After properly formatting your image, you are ready to register it. Under the Utilities pull-down menu, select Data Import –> Image Registration. This brings up a window for displaying your .rgb image on the top half and a data file for georeferencing your .rgb image to real world coordinates on the bottom half. Choose your .rgb image file by selecting the Image File button.

Your image will appear in two frames (Figure 1); the right frame shows the whole image and the left frame shows a close-up of the image (designated by the red box in the right frame). To navigate around the image, follow the directions in the green message area in the lower righthand corner of the window. When selecting the data file for the bottom half of the window, please note that it has to be a 2D grid or an ASCII data file.

Now you are ready to match three points between your image and the data file. After you have located your first reference point on both the image and the data file, zoom in close enough to view the white center square in the left frame of the data file. That white square highlights the exact location of the pixel to be selected (the exact coordinates are displayed in the green message area at the bottom of the window). To select the pixel, click the right mouse button. Repeat this procedure on the image file. These steps will reference the .rgb image to real world coordinates of the data file.

For ultimate precision, use the arrow keys on the keyboard to maneuver through the image pixel by pixel. Next, save your image registration file using the .imreg suffix (e.g., sand.imreg). To view the draped image in the 3D Viewer, first choose the Select Registration File button in the Image menu, and then select the corresponding .imreg file from the list that appears. Finally, select the Image Drape Display button, and your draped image will appear, as shown in the examples in Figures 2 and 3. Figure 2 shows an example of a draped image in plan view, while Figure 3 shows the same image in perspective.

 
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Last updated: March 22, 2007