Building  Ground Slope Diagram
In case 1:, with nearly flat terrain, the trees (*)
are probably treated as buildings. In case 2:, we
consider a ground slope near 33% grade as a steep hill. If the ground
If we don't consider the terrain, it is considered as a
continuing high rise building which could slip out by our
********* +40% (filter 0), of adjacent data points. However, by
******** subtracting off ground slope, it becomes more sensitive
**** to the filter with the lower values. If we use the ground
elevation at the mid x @ + and subtract off, the trees
Case1: may reduce to < 2 stories. However, for trees over say
______________________ 40' (42' for telephone poles), they may not. What is best
is to subtract off every ground level data point possible
********* to obtain the real building height, but use the lowest & highest
******* point to calculate the building's ground slope. Thus we add another
***** filter here to eliminate trees. A few example pics from Google Earth
Case 2: ________ back at the main page shows these effects.
______/
_____/ In case 3:, we have a steeper grade so certainly no building.
However, for a more gradual sloping hill what do we do?
First, we consider any building > 1200 to be trees. The longest buildings
I have seen are warehouses, about 1000' long, mostly in the suburbs but
only 12 stories high for tractor trailer loading, unloading's. However,
within center cities, we found PHL & PIT Convention Centers near 1000' but
diagonally, they could be near the 1200'.
After examining buildings in Google Earth, we have a dz = Delta Z, and the
max diagonal distance by dis. It appears that most all buildings won't be built
on a 10% slope but this rule may change out on the west coast. If we consider
Case 3: the diagram below, leveling a ground before the building would take the highest
** section and plow it over to the lowest  considering a constant slope. Therefore,
***** the building's base would be at midway between the highest & lowest point or dz/2.
***
** __ +++++++++++++++++++++++
** ___/ ! !
___/ > ! ...! zmax
_/ dz' ^ b ! ....: !
__/  h ! ....: !
    dis    ! .....: !
dz !....: !
 .....: dz/2
 .....:
zmin ....: .... < 10%
Consider the diagram is > 10%, a higher building towers above the slope. However, a long building
would have a hill pile of dirt at the upper end and expose basement at the lower end. How much of
a pile would is considered? A best guess would be to look at our example in PIT. Considering below,
__________ bh

 Calling ~~~ as the ground, or a bank against the side of the building,
 if it exceeds 1/4 the building height, probably no building there but
 trees. Above, we just quantified that the 'bank' would be dz/2. So the
 bank filter is if dz/2 > bh/4, then bh is probably trees clinging to the
___ bh/4 side of a hill, which is clearly shown in the PIT pics. Considering all
~~~~~~~~~~~ these filters apply to trees, let's put a cap on tree heights. Again, the
__________0~~~~~~~~~~ PIT pics show trees up a hill and correcting for the hill's slope, we may
have trees as high as 235'. So all these 4 filters apply for bh's < 235'
as the pic filters & stats show.