dem - Irregular XYZ point data to raster (TIF) - LASTools alternative?

I am trying to convert my irregular spaced point data (xyz) to a DEM and then, to a raster (geotiff). Because of the irregular spacing I need a triangulation first, right (so, no spaces are in the final raster)?

So the way is: XYZ -> Triangulate -> Interpolate To Raster. I have a lot of points (minimum 150.000), my raster size should be 0.25 x 0.25m or smaller. I need a way to do this with open source / free tools!

What I've tried so far:

• 
  

  LASTools (las2dem) - works great, is extremely fast <- that would be exactly what I need, but is not free.

  
  


• 
  

  FUSION (TINSurfaceCreate then DTM2ASCII) - works well, but slows down extremely as the raster size shrinks (1 x 1m and 0.5 x 0.5m is okay, everything below is really slow).

  
  


• 
  

  SAGA Tools / gdal_grid (via QGIS) -> extremely slow as well.

  
  

Any other suggestions I should try?

Answer

So, my workaround was the following: I am using FUSION for triangulation and raster calculation. it puts a *.dtm file out (binary) -> the conversion with the FUSION tools DTM2ASCII is the bottleneck.

So I got my hands on the binary reader of C#, read the entire *.dtm file and wrote my own tif-output with libtiff.net (http://bitmiracle.com/libtiff/).

It is not as fast as LAStools, but for my needs it is okay and works fairly well :).