How to set a fixed ratio for fence slope in the DTM?

[Art V]

For a project I need to determine the location of leveled areas relative to each other based on a fixed slope ratio (e.g. 1:3) and the height difference. Once the area locations have been determined, a cut and fill calculation will be done.

For example:

slope ratio 1:3

level area 1 = +30m

level area 2 = +10m

This will result in a 60m wide slope between the two areas.

The documentation mentions a maximum distance and maximum angle for the fence slope settings.

If I understand it correctly this means the angle might be less than the mandatory ratio but I need the slope of the fence to be an exact ratio (or angle which can be derived from the ratio).

My guess was to set the maximum distance greater than the largest distance between two areas and the maximum angle at the desired angle, but the somewhat ambiguous documentation does not give me enough confidence this will work.

How can I make sure that the slope of the fence has exactly an e.g. 1:3 ratio in all directions (not just between the two areas but also into the surrounding terrain)?

[islandmon]

1:3 = 18.4346? slope = 1.054 length scale factor from the horizontal plan distance.

Or 0.9486 of the slope distance to derive the plan distance.

[Thom]

islandmon

I am confused how you got from 1:3 to your answer. Would you expand your methodology?

thks - I am sometimes very brain dead from dealing with bureaucrats.

by the way, at least one of the tech support guys could not tell me how to get from 1V:3H to degrees

Edited May 20, 2008 by Thom

[Art V]

islandmon,

Thanks for responding.

Maybe I should have been more clear in my question.

The Dutch version mentions two things when creating a fence:

- create by distance

- create by slope

In the latter case you can set two things:

- maximum distance

- maximum angle of the slope

The documentation states that "maximum distance" is the maximum extent to which the slope of the fence will go.

Maximum angle is simply the maximum angle of the slope, and this suggests that VectorWorks may use a smaller angle.

In this case the distance of the slope is less important when it is going in other directions than inbetween two leveled areas, and depending on the terrain the slope distance can vary greatly from one edge of an area to another edge. I assumed the "maximum distance" setting will prevent the slope from going on indefinitely.

What I need to be absolutely sure of is that regardless of the slope distance, the ratio will be exact throughout the entire slope (e.g. 1:3 in my example) in all directions.

Maybe it is a matter of somewhat inaccurate translation into the Dutch VectorWorks and that the "maximum angle" simply should have been "angle".

In your experience, is the angle you get when creating a fence the same as the angle you typed into the settings dialog, or have you experienced smaller angles as well?

If you have experienced smaller angles, do you happen to know VectorWorks can be forced to use the exact ratio (or angle) that one wants to achieve?

Thanks in advancefor any help or insight.

[Art V]

Thom,

You can get the angle etc. in several ways:

The easy way is to use VectorWorks:

1. draw a (polygon) triangle with the horizontal line being 3 times the vertical line

2. use the arc dimension tool to dimension the angle between the horizontal line and the diagonal, this will give you the angle.

3. dimension the diagonal and it will give you the length

4. because you also know the lenght of the horizontal, you can calculate the ratio of the horizontal and diagonal distances.

Another, more classical, way is to use the sinus/cosines/tangent calculations

Since you already know the horizontal and vertical distances, you can calculate the tangent

e.g.

tan = vertical length/horizontal length

So with a 1:3 ratio the tan = 1/3 = 0.3333

inverse tangent then gives the angle, which is 18.4349 degrees.

With Pythagoras formula you can calculate the length of the diagonal.

[propstuff at MJLA]

Re getting the angle of a slope from its Run and Rise (X&Y); draw a line with the appropriate X&Y distances and then select Polar Coordinates in the Object Info Pallette (OIP)

Read the angle and length (diagonal) of the line from the OIP

Re constraining the slope; You can't with the Fence from Pad command. Max slope will be supposedly the Maximum slope not the nominated slope. It also didn't work in the test file I just made.

Regardless of the slope distance, it made a varying slope which was steeper than the 18.46? I entered in some places.