In preparation for the site transformation it was necessary to find suitable survey marks using the SCIMS database. In this case the criteria for suitable marks were that 4 survey marks would form a rectangle with a fifth survey mark in the centre of the marks. The marks that were chosen were PM51311, SS35647, PM50063, SS75016 and SS36313. The layout of these marks is shown in figure 2.
Figure 2: The survey marks used in the site transformations
Once the suitable marks were chosen and located, their coordinates were downloaded. These coordinates were then prepared in the required file format (Mark, Easting, Northing and Height) and uploaded to the rover.
After completing the above steps the fieldwork beckoned. Once the rover was set up and levelled over the first mark the point ID was entered and a CORS site (UNSW) was chosen. Observations were taken for 30 seconds or longer if a fixed solution hadnít been generated. A new CORS station (Chippendale) was chosen and observations were again taken on that mark for 30 seconds or longer. A third repetition was undertaken with another CORS station (Villawood) on the same survey mark. The above process was repeated for all other survey marks.
With the survey completed the data was exported onto the computer. The Leica GeoOffice software (LGO) was used to process the data. A new project was created into which the survey data was imported while the control point data was imported into another project with the UTM56 projection and GRS80 ellipsoid.
The one-step, two-step and classic 3D transformations were performed using the ĎDatum & Mapí option in the tool menu. The survey data in WGS84 and control point data in MGA94 was specified along with the type of transformation (one-step, two-step or classic 3D). Once this was done the points were matched and the transformation parameters were calculated. A report was generated which showed the transformation parameters and the residuals of the position and height of the survey marks. The transformation parameters allowed a local coordinate system to be created which was subsequently attached to the project. Using this local coordinate system the MGA94 coordinates as given by GNSS were compared to the MGA94 coordinates as given by SCIMS and the differences recorded.
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