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Dr Ian Plummer

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Technical
LIDAR - End of the Home Advantage?

Fed up with getting caught out by your opponent's local knowledge of their lawns? Use satellite mapping!

Recently it was noticed that you could download ground height data produced by LIDAR (Light Detection and Ranging, is a remote sensing method that uses light in the form of a pulsed laser to measure ranges) taken from aeroplanes and satellites. The scientists at Oxford Croquet's labs set to work to see what was on offer. After a little programming they had contour maps.

Taking an anonymous London club, with blue and white striped tents, it was found that the data was high quality and showed the topography of the lawns:

The optical view (courtesy Google Maps)

And the LIDAR height data:


Start Date Flown: 2003-02-22, End Date Flown: 2012-04-16.

The LIDAR data is collected on a 50 cm grid in this instance and was acquired by the Environment Agency for flooding investigations. The contour colours cycle from red-turquoise, red-turquoise, etc. as the height increases by the indicated width of the colour band.

The OxCr Software allows the absolute height of any point to be displayed by hovering the mouse pointer over it (images here are simply print-outs from the programme and do not display heights). 

The following was noted:

  • lawn 4 had a nice hill running N-S between hoops 1 and 2
  • lawn 3 had a 10 cm rise from left to right
  • lawns 5 and 6 had undulations of ~3 cm
  • lawn 2 was below river level in the image and had undulations of ~4 cm
  • the black line on the plot likely shows the boundary between two scans stitched together by the data gatherers
  • the noise on these images appears better than 1 cm. Setting the contour band to 1 does not produce a speckled image over the lawns.

These lawns are extremely good and show the power of the dataset and ease of obtaining it.  There are richer datasets available where each point contains additional parameters such as the strength of the returned signal. 

To put the ease of data collection into context, to map out a croquet lawn including a 1-yard selvage with a surveyor's pole and theodolite would require 1200 measurements at 1-yard spacing, or 4800 at ½-yard spacing.  A downside of the LIDAR data is that it is a compilation of a number of flights, resulting in stitching errors as shown by the black diagonal line above and also the date of the data collection has a wide span. The past tense was used above since the data was collected between 2003 and 2012 for that location.  The lawn topography may have been improved since those measurements were taken.

The following from a midlands club (1 m grid) showed the Oxford University team, before they got there, that the lower three lawns sloped off to the south by 7 cm!


Start Date Flown: 2010-01-28, End Date Flown: 2010-01-28

To show some poor lawns, below are those in the Oxford University Parks:

 

Here the contour bands are 3 cm steps and show 10 cm undulations and the boundaries falling away (1 m grid).

 

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LIDAR mechanism

LIDAR Data: Public source (hint: push the boundary between the map and the text up to see anything useful!) & Academic source (academic login required)

LIDAR data here was sourced from: Lidar Composite Digital Terrain Model England [ASC geospatial data], Open Government Licence, Using: EDINA LIDAR Digimap Service, <http://digimap.edina.ac.uk>

All rights reserved © 2017-2017


Updated 28.vi.17
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