Thinned Grid

PhotoSat Thinned Survey Grids

PhotoSat thinned grid

The points in a typical thinned grid generated by PhotoSat’s grid thinning system. Points are removed if they are less than 10m from the nearest adjacent point and can be interpolated to within 10cm in elevation by the surrounding points. No points are removed near changes of slope.  This preserves most of the detail in the original survey grid.

ASCII XYZ is the most common mine planning and engineering software input format:

The most common input format accepted by mine planning and engineering software is ASCII XYZ format.  In this format each data point is represented by Easting, Northing and elevation values, and is equidistant from its neighbours in the East-West and North-South directions. 

Long data import and reformatting times for ASCII XYZ grid files:

Most mine planning and engineering software convert ASCII XYZ files to the system’s proprietary mine grid format.  For an entire mine site the ASCII XYZ files can be tens of gigabytes in size. The import and reformatting process can take many hours for large ASCII XYZ files.

Grid thinning to reduce data import times:

Grid thinning is the process of removing points from large datasets to reduce their size. Since the resulting dataset has fewer points, grid thinning can result in a loss of fidelity.  The thinning process has the potential to reduce survey grid resolution and accuracy.

No available commercial survey grid thinning programs produced adequate results:

PhotoSat tested several commercially available grid thinning programs to produce a more compact product that could be more quickly imported by PhotoSat’s mining customers.

The commercially available programs were tested by first thinning the original survey grids.  We then produced Triangular Interpolated Network (TIN) surfaces and new grids from the thinned points. The TINs and new grids were then compared with the original survey grids. PhotoSat found elevation differences of over a meter in every test of commercially available grid thinning programs. 

We concluded that the existing commercially available software would not be adequate for our customers’ requirements.

PhotoSat grid thinning process:

PhotoSat developed its own proprietary grid thinning process for producing accurately thinned grids to help overcome the data import bottleneck.

Since grid thinning is a computationally intensive process, PhotoSat developed its system to run on modern Graphics Processing Units (GPUs). GPUs perform numerical calculations more than 100 times faster than conventional Central Processing Units (CPUs).

Original 1m grid points and thinned grid points generated by PhotoSat’s grid thinning system.

Original 1m grid points and thinned grid points generated by PhotoSat’s grid thinning system.

For a typical mine site survey grid, the PhotoSat thinned grid has only 10% of the points of the original 1m grid. When re-gridded and compared with the original grids, the elevation differences are less than 10cm. 

Very minor elevation differences between a PhotoSat thinned grid and an unthinned grid

On the left an image of a 1m grid reproduced from a thinned grid. The difference image on the right shows that 90% of the re-gridded points (LE90) are within 3.5cm of the elevations of the original points.  This is a very small accuracy trade-off for a 10X improvement in data upload times.