Uk Os Dtm

[colinsmith]

Is there anybody with experience of using UK OS DTM files that can give some guidance on workflow?

 

I have access to NextMap 10km x 10km tiles in ntf format and am looking for a nice way to get to a polygon mesh for Rhino and/or Lightwave.

I've tried hunting down some free translation utilities on the net, but nothing has worked 100%, maybe because they expect 10m data to be in the form of 5km x 5km tiles? MicroDem certainly seems to have that problem.

 

This GIS stuff is all new to me, so a point in the right direction would be a big help.

[derijones]

Have a look at Daylon Leveller - it imports NTF data and produces polygon meshes that can be output in a variety of ways. Not too expensive for the full version.

Hope it helps

Deri

[colinsmith]

Affraid Leveler is another one to add to the list of programs that don't like my Nextmap ntf files....

[derijones]

Ahh...

Have you tried Easysite for Rhino - reads in raw point data and creates meshes - I don't know what format NTF files are but if it's basic XYZ point data in a text format, then it might read them.... you can then create a mesh in Rhino using the tools and export to LWO / OBJ format.

[colinsmith]

I've been able to get the ntfs exported as dxf point and contour files, so I'm planning to try those out in Rhino. I have a demo of "Terrain for Rhino" which should do a mesh from the points in one/other/both of the dxf files, but as it's 2000x2000 base points per tile I'll have to see how painful the whole operation is...

I need the full accuracy for part of a tile, and then can see about reducing the poly count as it moves into the distance.

[colinsmith]

Sorry, to explain the root of the problem a bit further.

 

NTFv2 is the format that all Ordinance Survey terrain models come in.

The 30m and 10m resolution files have been about for a while now and have some support.

The Nextmap files I've got are 5m resolution and none of the ntf importers seems to be able to deal with those directly.

 

The NTF format is almost in an xyz ascii form, but just a bit too mixed up for me to be able to figure out at the moment. At 2000x2000 points any conversion needing any manual input is a bit of a pain.

[derijones]

Colin

Easy site allows you to create contour lines from point data and edit the number of contours and then create a mesh from those - you can delete out every other contour or so in the areas that you don't want and keep the detail where it's required as well as doing other mesh editing commands - using polylines to select areas, delete the mesh and fill the hole with lower res etc.

I've only just got it, so I've not tried it out in anger yet, but it seems to work OK on a 1K mesh when messing about.

A 2Kx2K mesh will cause it to choke - it uses well over a gig of RAM just to create a mesh that size.

Sounds like your getting there - let us know how you get on!

Cheers

Deri

[colinsmith]

Thanks for the ideas Deri.

 

I've just tried out Terrain for Rhino in demo mode so far, but it seems to do much the same as EasySite. The problem I see with working from the contours is that they have a very high number of points, so it would need manual selection to be anywhere near resonable.

 

The 2k x 2k DXF point mesh is not really viable to edit in full. Just opening that in Rhino brings my 2gb ram system near to crashing.

 

For now I think I'll end up having to do a mixed solution - building the low detail areas in polys by hand from the contours and trying to export only a limited area as 5m res point data for where I really need it. I'm hoping that I can cut it down to more like a 200x200 point grid and that will bring it to where the automated tools can come in again.

 

I'm still waiting to see if the project gets the go ahead, so for now I think I have good enough idea of the difficulties that will come up, and I'll wait to see if I have to deal with them or not ;-)

[colinsmith]

Just a quick update of my progress in case it helps out.

 

MicroDem will now open 5m grid UK OS DTMs in ntf format, following some update work from the helpful developer.

That will let you open, resample (if required) and export the DTM as a DXF or OBJ mesh.

 

The other program that has been useful is Global Mapper which is a very nice low cost GIS/Terrain mapper program. At the moment it doesn't open the ntf files, but I was able to have the DTMs resupplied in an ASCII xyz format and that simplified thing a lot - definately worth doing that if it is an option.