Rectifying Images

RockWorks | Graphics | Images | Georeference

This program is used to calibrate, rotate and clip airphotos and satellite images to project dimensions. Optional generation of an accompanying World file is available. Supported bitmap formats include: BMP, JPG, EMF, WMF, PCX, PNG, TGA, and TIFF.

The basic idea behind this program is to take an image, calibrate it to user-defined coordinates, rotate it such that the edges are aligned to a north/south, east/west orientation, and then to clip (extract) the portion of the image that corresponds to a rectangular area of interest. Subsequent uses for the output image include backgrounds for 2D maps and draped/floating images for 3D diagrams.

Feature Level: RockWorks Basic and higher

Menu Options
Step-by-Step Summary

Menu Options

• Options
  • Input: Click to the right to browse for the image to be rectified. The supported file formats are listed above.
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  • Output: Click to the right to type in a name for the new image to be saved by RockWorks. The supported formats are shown above. We recommend you save images to be used with the current project data, to the current project folder.
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  • Calibration Method
    • Project Corners: Choose this option if you will be digitizing the northwest, northeast, and southeast corners of the current project extents. For this option you don't need to type in the calibration coordinates.
    • 3-Points: Choose this option to type in known coordinates for three points on the map. They can be in any orientation, but remember the order in which you list them - you'll need to click on the points, interactively, in the same order in the next step of the process.
      • Point 1: Click on the X and Y prompts to type in the X and Y coordinates for the first known point you wish to digitize on the image.
      • Point 2: Click on the X and Y prompts to type in the X and Y coordinates for the second known point on the image.
      • Point 3: Click on the X and Y prompts to type in the X and Y coordinates for the third known point on the image.
  • Clip Image: Insert a check here if you want to crop the image, and establish the crop dimensions below.
    • Based on Project Dimensions: Choose this option to have the program crop the image using the current output dimensions.
    • Based on Custom Dimensions: Choose this option to type in specific clipping coordinates. Expand this heading to enter these coordinates.
      • Western Border (X-Min): Click here to type in the coordinate that is to become the left (western) edge of the image.
      • Southern Border (Y-Min): Click here to type in the coordinate that is to become the lower (southern) edge of the image.
      • Eastern Border (X-Max): Click here to define the coordinate that is to become the right (eastern) edge of the image.
      • Northern Border (Y-Max): Click here to define the coordinate that is to become the upper (northern) edge of the image.
  • Create "World File": Check this box if you would like to create a "World File" that can be used in GIS (Geographic Information Systems) programs in order to correctly register (locate) an image relative to a mapping coordinate system. You will need to define how the World File name extension will be assigned. (The file name itself - the part before the "." - will be the same as the output image name.)
    • Append "W": Choose this option if the file name extension of the World File should have the output file name extension plus the character "w". Example: If the rotated/clipped output image is named "Project 27.jpg", the World File will be named "Project 27.jpgw".
    • Change Extension: Choose this option if the file name extension of the World File should have 3-characters:
      • The first character of the extension will equal the first character of the output file extension.
      • The second character of the extension will be equal to the last character of the output file extension.
      • The third character of the extension will be set to "W".
      • Example: If the rotated/clipped output image is named "Project 27.jpg", the World File will be named "Project 27.jgw".
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  • Show in Google Earth: Check this box to display the imported image in Google Earth.
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  • Set as Project Image: Check this box for the imported image to be set as the project image.
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  • Show report describing rectification accuracy: Check this option to see a report of the image accuracy when the rectification is complete.
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• Display 2D: Check this box to display the image as a 2D map at this time.
  Click this tab to set up the 2D map layers (labeled axes, map overlays, etc.). You can request both 2D and 3D display (below).
  • Output Options: Use these settings to define whether the output graphic is to be saved (or displayed as "untitled"), how the file should be named, and whether it is to be displayed after it is created. It also offers export options. (More info)
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• Display 3D: Check this item to have the image displayed in RockPlot3D.
  • Drape: Insert a check in this box to drape the rectified image over a grid (surface) model that exists in your project.
    ! Important: This tool will stretch the image to fill the grid model boundaries. It assumes that the image edges match the grid model edges.
    • Grid Model: Click on this to select the name of the surface model (.RwGrd file) that contains the elevations over which the image is to be draped. For example, if you have been working in the Borehole Manager, you might want to look in the Project Manager for an .RwGrd file with the name of your upper-most formation.
    • Layer Name: Type in a name for this layer; it will simply be used to label the bitmap in RockPlot3D. For example, if the image represents a satellite image, you might name this layer "Satellite Image."
    • Set Transparent Color: Insert a check in this box if you want to specify a specific color in the raster image to be displayed transparent. If activated, expand this heading to click on the color box to choose the image color that is to be set to transparent. For example if the image has a white background and you would like that part to be see-through, you would select white.
      • ! Note that this transparent-color selection is fairly precise. In high color images there can be considerable variation of white, for example, which can make it tricky to set broad transparency. For this reason, as well as for reasons of speed, it’s best to keep the bitmap colors to as few as possible.
    • Vertical Offset: Use this setting to offset the image above or below the grid surface, expressed in your elevation units. This can make the image and surface more easily visible in RockPlot3D.
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  • Float: Click in this box to float the image as a flat surface.
    • Elevation: Click here to type in the elevation at which the bitmap is to be floated.
    • Layer Name: Type in a name for this layer; it will simply be used to label the floating bitmap in RockPlot3D. For example, if the image represents a satellite image, you might name this layer "Satellite Image."
    • Set Transparent Color: Insert a check in this box if you want to specify a specific color in the bitmap image to be displayed transparent. See the notes listed above, under Drape.
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  • Other 3D Diagram Options
    Use these checkboxes to append other layers to your 3D scene.
    Click each tab to set up the 3D diagram layers (images, infrastructure, reference cage, etc.).
    • Output Options: Use these settings to define whether the output scene is to be saved (or displayed as "untitled"), how the file should be named, and whether it is to be displayed after it is created. It also offers export options. (More info)
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Step-by-Step Summary

1. The Georeference program reads an existing raster image; be sure you have that handy.
2. Select the Graphics | Images | Georeference menu option.
3. Enter the menu settings, described above.
4. Click the Continue button to proceed.

   The program will display the selected image on the screen. At the top of this display window, you'll see a prompt to "Click on Point #1 (of 3)".

5. Using your mouse, click on the point on the image that represents your calibration Point #1. If necessary, you can adjust the view size using the "Size (%)" prompt in the upper-left corner. Increasing this number (by typing in a value, or by clicking the up-arrow) will offer a zoomed-in view of the image. Decreasing this number will offer a zoomed-out view of the image.

   When you've clicked the first point, you'll see it posted on the image.

6. Click the point on the image that represents your calibration Point #2. It also will be posted on the image.
7. Click the point on the image that represents your calibration Point #3.

RockWorks will rotate the image as necessary, clip it as requested, and display it as requested:

• In a RockPlot2D tab.
• In a RockPlot3D tab, draped over a surface.
• In a RockPlot3D tab, floating at a defined elevation.
• In Google Earth.

Back to Image Menu Summary

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