Tuesday, June 26, 2012

Data Prep for JAG3D

Instructions for preparing your Photosynth data for JAG3D Transformation.

The basic data structure for JAG3D is a tab-separated text file without and header row.

There are two files that are required:
  1. Startsystem: Raw Photosynth data
  2. Zeilsystem: Target ground control points in the proper coordinate system
The columns for both files are

(#)    (x)                  (y)                   (z)

In order to georeference your Photosynth point clouds you will need ground control points (GCPs). I suggest you collect them with a high-quality GPS and have them well distributed throughout your study area. I strongly suggest you use UTM coordinates for your GCPs as this projection matches the Cartesian system from Photosynth.

Your ground control points will need to be matched 1:1 to points in your raw data.
The easiest way to do this is to find the points in the raw cloud that match your GCPs. The program CloudCompare (link the my software post) allows you to pick out individual points and retrieve their attribute info.
    • Open your PLY file in CloudCompare
    • Use the point picking tool
    • Save the XYZ info for each point that matches your GCPs into a separate text file
    • Open the PLY file in a text editor
    • Find the points you chose in CloudCompare and move them to the top of the PLY file. Save the PLY file as a text file
    • Open the text file in Excel, insert a column on the left-hand side and add sequential numbers down to the last row. (i.e. 1,2,3…)
      You will need to strip off the color information from the points, save it to another file and you can merge it back together later.
      Save this as a new text file. This is your Startsystem file for JAG3D
  • To create your Zielsystem file, create a file (Excel works for this) input your GCP coordinates in the same format (#)(X)(Y)(Z) and in the same order as the corresponding points in the Startsystem file.
  • Save this as a new text file.
It is important that the points that match the GCPs in the Startsystem are in the same order as the GCPs in the Zielsystem file. JAG3D will calculate the transformation by calculating the parameters to move point #1 in the Startsystem to point #1 in the Zielsystem, point #2 to point #2, etc.

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