Trying to understand Las_ground_new "7" (6) parameters

[Hildermes José Medeiros Filho]

Hello, Lasgroup,

I'm trying to make some pictures to understand better your PTD (Progressive TIN Densification) approach.

 

I'm finishing my college completion work and in one of the stages I used las ground new(the free version, I know it insert errors).

 

I wonder if those explanations  would be correct. 

 

- 1) Step, this define the first part of classic PTD, you will define a regular grid and select the lowest point as seed to start your desification.

(a) small step and bigger step (b), if we imagine that the scene (a) has a large build, this could lead to misclassification.

- 2)Sub[1 - ??] I did not understand what this means.

- 3a) Up Spike, 3b)Down spike, as martin defined " is used between refinement passes. After each we check in the current TIN if any of the inserted points forms too much of an up or a down "spike" with its immediate one-triangle-ring [2 - ??] of other points. If the observed spike exceeds the specified (vertically) it is removed.

Down spike

- 4) Bulge, as martin defined " the bulge affects how the triangle that the point under consideration falls into is interpolated at this points x/y coordinates to compute its z_int [3 - z interpolated?] [...].A bulge of non-zero means that the three normals of the triangles [4 you need 3 triangles, right? I think I Have to remake the picture] are used to "bulge" the triangle either up or down (depending on the normal direction) so tha z_int can lie "above" or "below" the triangle[...]"

-5) Stddev,  as Martin defined " It is a special option designed to, for example, get cleaner roads in steep mountains and not "chop off" so much of the road near the two steep sides[...]"

I could have drew a mountain and road, I will try to do so later.

- 6) Offset,  With bulge  you had created a way to have a z interpolation of the point, we need now to decide how far from that point the real z can be.

If the real point respects the bulge and offset we have a "ground point" [5 - I'm Right?]

Thanks in advance!

references:
1 https://groups.google.com/forum/#!topic/lastools/GRSSE36x-ZI

2 https://groups.google.com/forum/#!msg/lastools/ZXLnRbFu0xw/ovfvuhiyAQAJ

3 https://groups.google.com/forum/#!topic/lastools/pM-h0L7XPnk

4 https://groups.google.com/forum/#!searchin/lastools/if$20you$20run$20lasground$20or$20lasground_new%7Csort:date/lastools/MRaIIBFBdVA/aUq4C1WmCgAJ

[Hildermes José Medeiros Filho]

I think I should put things in order. For clearance of ideas:

1) Step, this define the first part of classic PTD, you will define a regular grid and select the lowest point as seed to start your desification.

2)Sub step, now I think i understood this, It pushes the "step box" a little to (right and down, for example), doing so, it does a better feeding.

3a) Up Spike, 3b)Down spike, In my concept this helps us define if a seed is way down or way up a limit we defined.

4) Bulge, The bulge will define the surface expected behaviour, based in the triangles we have, using normals.

6) Offset, from this points ownard lasstools asks "our self" : (a) if the point expected  z (calculated with bulge) + offset respects the limiar this points goes to the TIN; else (b) the point is not a ground point.

5) Stddev, this parameter can improve the threshold of the offset (in fact you could just increase the offset manually)

Any way, I think this is it.