DTM height data

[Angry Haggis]

Known issue:
http://rapidlasso.com/2015/09/02/englan ... esolution/

Jagge, as my own post above states, that they are supplied to millimetres - actually cm with a trailing 0. Ie. 3.290 metres.

[Jagge]

Ah, good to see they are fixing those decimal issues.

I am afraid lots of useful data is lost when data is processed to DTM/DSM. There is several returns in raw data, and those area valuable information to figure out vegetation density at 1. .. 3 m from ground under high forest canopy. Most of that is lost, what is left is essentially just roof and ground. In addition it is valuable to know is DTM/DSM points interpolated or actual true points. Often there is areas with no ground points indicating there is something dense enough to not let any beams go all the way to the ground, like rock or dense bush. now here we have just interpolated points with no way to find out what is it interpolation or actual ground. Also to figure out cliffs it is useful to know actual ground points (to generate TIN), no way to do that with this interpolated grid. And if needed one could re classicy and generate DTM and DSM the best way for the task instead of using these pre-processed default ones made for something else in mind than O mapping.

There may be some other issues like data being lost or skewed when DSM is made. I have played little with 1m data, here is example. As you can see at the top of the hill there is some kind of forest and trees but no sign of them whatsoever in DTM. Maybe leafs off season scanning results more points at ground than trees per same square meter made them use ground point to represent each square in DSM. So no sign of trees in data. I used 1m data, best available the area I happened to zoom in.

http://routegadget.net/misc/profileuk.jpg

But of course it is better than nothing, and not that bad at all and may not be that big issue for areas with no trees. But raw data would still be far better.