Understand the co-ordinate system
I’m going to be using geo-referenced data in this mapping project: each piece of information is going to relate to a specific place on the Earth.
The different sources of information will each use some kind of co-ordinate system.
The mapping software will take care of the conversions and details.
Getting LiDAR data requires the use of UTM co-ordinates. UTM co-ordinates have three parts to them, and might look like this: 55H 689579 6097682 (that’s a point in our map area).
- 55H represents the UTM zone. There are 60 longitude bands, each 6-degrees wide, around the Earth. Our point is in the 55th band, spanning longitudes from 144-degrees east to 150-degrees east. The ‘H’ represents the latitude range. There’s a map of UTM zones in the Wikipedia UTM entry.
- 689579 is the UTM Easting. It represents the east-west position. The reference line is the line of longitude running through the middle of the UTM zone, and it has the value 500,000. Values greater than that are to the east, and vice-versa. The units are metres. The example point is therefore 189.579km east of the 147-degree longitude line.
- 6097682 is the UTM Northing. It represents north-south position. The reference line (in the southern hemisphere) is the parallel of latitude that’s 10,000km south of the equator — it is just 2km from the south pole. The reference line in the northern hemisphere is the equator. The units are metres. The example point is 6,097.682km + 2km north of the south pole.
I use the UTM eastings and northings when acquiring and manipulating LiDAR data files.
My mapping project is going to be contained within these UTM co-ordinates, from zone 55H:
- South-west corner of the map area: 688600 6096750
- North-east corner of the map area: 690325 6098200
This article is part of the Orienteering Mapping with LiDAR, Smartphones and Free Tools series.
Polite and constructive responses are always welcome.
