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Using Site Scan and ReCap 360 Pro to set manual ground control points

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The GPS module on board Solo drone is accurate down to around 10 feet. Many Site Scan customers wish to tie their final orthomosaic, mesh, or point cloud to an absolute coordinate system with more accuracy. This is possible with Site Scan and ReCap by setting manual ground control points in the ReCap web app.

 

  1. Scan or Survey your object of interest.Don’t know whether to perform a Scan or a Survey? As a general rule, if your area/object of interest has vertical faces, use the Scan tool. Otherwise, use Survey.
  2. Geotag your images, upload the images to the 3DR Cloud, and initiate processing with Autodesk ReCap. For this workflow, make sure you select RCM as one of the data outputs.Confused by Autodesk file formats? Ortho will generate an georeferenced aerial map and digital elevation model, RCS will generate a point cloud for use in Civil 3D and other Autodesk products, RCM will generate a mesh for use in ReMake, FBX will generate a mesh for use in other Autodesk products, OBJ will generate a mesh for import into all 3D viewers, and LAS will generate a point cloud for import into all point cloud viewers.
  3. Wait until processing is completed. Monitor job progress using Site Scan Manager
  4. Navigate to the Autodesk ReCap web app at https://recap360.autodesk.com/. All of your projects should appear as tiles. Click the project that you would like to reprocess with surveyed ground control points.
  5. Click the “resubmit” button under the home icon

 

6. This menu allows you to add or remove images. If you do not wish to add or remove any images from the processing, click “survey settings.”

 

7. Survey settings will allow you to set manual ground control points. Select an image from the pane at right that contains one of your ground control points then select an image from the pane at left that contains the same point.

 

8. Use the reticle to select the same point in both photos. The scroll wheel on your mouse zooms in.

9. Click the pin to add the coordinate that particular ground control point. XYZ is used for local reference frames, ECEF for Earth-Centered, Earth-Fixed, and LLA for lattitude, longitude, and altitude. I almost always use LLA.

10. Repeat steps 7-9 until you have injected all of your ground control points. Typically six ground control points per large Site Scan flight generates a result with several centimeter absolute accuracy. Each ground control point should be identified in 3-4 individual images.

11. Click “settings” and look at the options. Smart cropping automatically crops the model behind the camera and should usually be turned on, smart texture improves the texturing at the expense of processing time, nadir optimization should be turned on for a survey and off for a scan, and formats should be selected as within the Site Scan mobile app. Once you are happy with your selection, click “create.” The project will be resubmitted with the ground control points.
Screen Shot 2016-06-14 at 6.24.44 PM

12. The new result should be accurate to within a few centimeters. The images below show a surveyed ground control point superimposed on both an orthomosaic that was generated with and without manual ground control points. Notice that the survey point (green dot) is off by 10 feet or so in the latter and right on target in the former. The target, if not clear, is the cross painted on the road.

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