Sorry if this is a completely obvious one, but I am a complete beginner with TransDEM at the moment. Can you tell me what the numbers at the end of the grid lines on DEM grids are for? (eg numbers in purple colour such as 490000 and 500000). Many thanks for any replies and apologies for asking newbie questions
Bill
ref numbers on grid squares in DEMs
Re: ref numbers on grid squares in DEMs
These are geo coordinates. Geo data, as processed by TransDEM, uses a map projection (Mother earth isn't flat but maps are and the map projection assists us in making the world flat, at least for mapping purposes.)
TransDEM uses the UTM projection and it's a reference to UTM coordinates that TransDEM transfers to Trainz when generating a route. Most map projection coordinates are values in metres. For UTM, the northing (y-axis) is the distance from the equator to the point in question, usually a 7 digit number for the northern hemisphere. The easting (x-axis) is the distance from the central meridian of the UTM zone, plus 500 km, to make all values positive, usually a 6 digit number. UTM comes in zones, each 6 degrees longitude wide, a compromise because the world isn't actually flat.
In the UK you have a different coordinate system, the National Grid. It's similar to UTM but not the same. There is only a single zone and the eastings and northings are 6 digits. Sometimes the leading digits are replaced with a letter code, indicating a square of 100 x 100 km.
The TransDEM main manual has an extra chapter on geo coordinates systems and how they are used by TransDEM.
TransDEM uses the UTM projection and it's a reference to UTM coordinates that TransDEM transfers to Trainz when generating a route. Most map projection coordinates are values in metres. For UTM, the northing (y-axis) is the distance from the equator to the point in question, usually a 7 digit number for the northern hemisphere. The easting (x-axis) is the distance from the central meridian of the UTM zone, plus 500 km, to make all values positive, usually a 6 digit number. UTM comes in zones, each 6 degrees longitude wide, a compromise because the world isn't actually flat.
In the UK you have a different coordinate system, the National Grid. It's similar to UTM but not the same. There is only a single zone and the eastings and northings are 6 digits. Sometimes the leading digits are replaced with a letter code, indicating a square of 100 x 100 km.
The TransDEM main manual has an extra chapter on geo coordinates systems and how they are used by TransDEM.
Re: ref numbers on grid squares in DEMs
Thanks for your reply. I appreciate the explanation and understand now what UTM coordinates are.
regards
Bill
regards
Bill