Hi,
I have been asked to complete some analysis to establish vegetation heights using a combination from LAS and DTM datasets. But I have some questions regarding the conversion of the LAS file to raster process. I am aiming to create a raster version of the LAS file and then subtract the z values from the DTM to find the vegetation heights
I am using FME 2015.1.0.2 build 15482.
I have read in the LAS file and have then used a point cloud filter to retain only classification 5 data. I then push the output to a numeric rasteriser to convert into a raster in advance of comparison with the DTM. My issue is that there appears to be no option to; account for, or set, the interpolation for instances where multiple point cloud data points fall within my stipulated cell size.
I ran the process anyway and I have completed some tests; and in the case where multiple points fall within a given cell, the resultant value of the output raster appears to be that of the last point cloud data point which goes through the cell (I think each value of the cell is overwritten each time a point is seen in the cell. Therefore the resultant cell value is purely derived on its order within the file and not through any ‘known’). I have also then checked the assigned values of the cell against all of the points which are were within the cell. Needless to say the delta can be substantially different in some instances for all the values within a given cell. I would really like to be able to control how the resultant cell value is assigned in these instances of multiple containment, i.e. min, max, avg, etc. Can anyone suggest a method to do this?
As an aside I have also created an alternate method of exploding the point cloud into points and then obtaining the diff with the DTM using a point on raster, but the problem is the amount of points within the LAS file is huge (unsurprisingly) and it is slow (or impossible in some situations for my computer to cope). Therefore I think that I definitely need to use a raster approach in the first instance for fine the vegetation height.
Thanks in advance,
Regards,
Rob