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Georeferencing Imagery Using Well Locations in Surfer

Over the past few years, many of our Surfer users have requested true georeferencing capabilities inside the Surfer application. The requests we received were focused on having the ability to use internal points within the image to georeference it; where warping techniques can be applied to get a good fit to known ground coordinates. Previous versions of Surfer allowed the corner coordinates of images to be defined in order to locate the image in a different coordinate space. However, this functionality did not offer a way to account for any warp in the image and required extra work if the corner coordinates were not known. Surfer 14 gives you just what the doctor ordered; full georeferencing functionality that uses any number of control points and gives you your choice of 10 different warping methods.

Let's use this new functionality to a real-life application. The remainder of my blog today will be focused on georeferencing an aerial image, captured by drone, of a brine storage facility in Surfer 14. The composite drone image was acquired by the storage facility management team to be used in a conceptual site model of the facility. Additional contour layers, base layers, and post layers would be overlaid on the aerial image. Known monitoring well locations within the aerial image can be used to georeference it, creating a good base layer to create the map on. The image I am using in the following example was post-processed to emphasize the monitoring well locations, which made it easy to identify the locations where the control points needed to be added.

Before the image is georeferenced in Surfer, it will need to be imported into a project as a base layer. This can be easily done by clicking Home | New Map | Base. Once it has been imported, it can be georeferenced using the following steps:

  1. In the Contents window, expand the Base Layer so you can see the image and select it.
  2. In the Properties window, click the General tab, and click the Georeference Image button
  3. The Georeference Image dialog opens, use the mouse wheel to zoom into the image so the well locations are visible.
  4. Click the Add Mode button, which will add control points within the image.
  5. Click on the first well location in the View Pane to add the control point.
  6. In the Control Point Table, enter the real world coordinates in the Target X and Target Y fields. 
  7. Repeat steps 5 and 6 for the other well locations. Surfer requires at least 2 points to georeference an image; I recommend using more. In this example, I used all 15 monitoring well locations within the site. This was probably a little overkill, but I wanted the georeferencing to be as accurate as possible.
  8. After I added the control points, I needed to make sure I had the correct Warp Method set. By clicking Edit | Set Warp Method, I can see what the method is set to. By default, the method is set to Automatic; which tells Surfer to use the number of control points to determine the method. Because I have 3 or more control points, Surfer automatically uses Affine Polynomial which is just fine for these purposes.
  9. To georeference the aerial image and update the map, click File | Update Map or click the button.
  10. Finally, click File | Close to close the Georeference Image dialog.
All monitoring well locations within the image have been used as control points for the georeferencing process.

The composite drone image has now been georeferenced and the Surfer map has been updated, which creates a nice base to build a project on. Additional georeferenced files, contour layers, post layers, etc. can be added to the project. This user-friendly workflow makes it easier than ever for Surfer users to incorporate all sorts of mapping data, contour maps, point data and aerial images into their Surfer projects, including unreferenced imagery captured by UAVs!

The final conceptual site model that uses the aerial image that was georeferenced in Surfer. Post layers and contour layers have been added to the map.
 

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Saturday, 18 November 2017

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