Tutorial
12
In this exercise you will learn how to;
¨
Use the maximum triangle side to limit where
contours are formed.
¨
Select and delete individual triangles.
¨
Select and delete triangles within a polygon.
¨
Enter boundary strings into a Contour model.
¨
Use boundaries to remove unwanted contours.
¨
Use boundaries to remove unwanted triangles.
.
You have been provided with a Job named “Boundary.CDSdb” in the Tutor
folder and you should Start Ezicad_Premium, and use File Open to access it.
The screen should
similar to that below
Now select Contour, then Surface Parameters and select reset to make
sure the program reads the full extent of heights in the job. Set the Major Contour interval to 2 and the
Minor Interval to 0.5.
Also reset the Surface Point Selection to use all the points in the job.
Next Form the Model. (Note since we wish to use the extents of the job
as the Surface Area, there is no need to access this option as Extents is the
default.)
Now calculate the contours and allow them to be saved. Your job should
now look like that below.
Now while this may at first appear to be a reasonable result,
particularly if you have never seen the site, I regret to inform you that it is
not quite correct, and there are a number of areas where triangles and contours
are formed when they have no valid reason to be there.
For example on the southern area of the job, there is a run of points
around a ‘curve’ from point 230, through 130 and up to 137, and these points
are in fact around the boundary of the particular parcel of land.
Likewise, on the eastern boundary there is another ‘curved” run of
points from 239 in to 204 and up to 214, and these points also follow the
boundary of the land.
Now, your client will complain enough about your fee for providing a contour
plan of her land without having contours drawn on the neighbours’ block as
well, so we need to examine ways of removing the excess contours.
In broad terms, you can either prevent the triangles forming over the
areas in the first place, or remove them after they have formed, and there are
essentially three ways in which you can go about this exercise.
1. Limit the maximum triangle
side to prevent ‘large’ triangles forming.
2. Select triangles, either individually, or
within a polygon and delete them
3a. Insert strings around the excess areas and
remove contours inside the strings
3b. Insert strings and remove
the triangles inside the strings.
1.
Limit the Triangle Side
The first method is rather crude in its application, and it is best
suited where there are large concave excess areas, with a good coverage of
points in the remainder of the job.
If you look closely at your points you will see that you really don’t
wish to form any triangles that have a side larger than the distance between
points 210 and 204.
So, press ‘J’ to get a join between these points and you will find out
that the distance is a little over 85 metres.
Now pull down your Contour Menu, select Surface parameters and set the
Maximum triangle side to 85 as seen in the screen at right.
Once this is accomplished, you should again pull down the contour menu,
and now select Form Model.
The triangles should now appear as seen below right.
As you can see, we have removed the triangles in the concave areas, but
we have been a little over enthusiastic in 
other areas and
have left holes in the parcel.
While the tool of Maximum Triangle Side is not the correct one for this
particular set of data, it is important that you are aware of its capabilities
so you can use it where the data is more closely defined in the body of the
job.
Go back to your surface parameters, set the maximum Triangle side to “No
Check” and then re-form the model, and we will go on to show you a better
method of controlling where contours are drawn.
Once the triangles have been formed, you can either select them
manually, as described next, or enter in closed strings to contain and delete
the unwanted ones, and it is up to you to learn the various methods, and then
decide which method is most applicable to the job in question.
2.
Select Triangles and Delete Them
Now that you have the triangles reformed to their default state, we will
look at how you can manually select triangles and have them deleted.
Pull down the
Contour Menu, and select the Edit Model option.
You will see the various options as shown in the screen at right.
Select Independent Triangles
You can select individual triangles by simply pointing to them.
First you need to select this option, and you will see your cursor
changes to a crosshair with a triangle in the centre of it.
You then position this cursor within the triangle you wish to select and
press your left mouse button.
You will see the triangle changes colour to indicate that it is
selected.
You may then continue to select other triangles as needed.
Please note that if you select adjacent triangles, the ‘common’ side
will revert to its original colour, and only the perimeter of the selected
triangles will be shown in a different colour.
For example, in this job if you first pick the triangle made up of
Points 230,133 and 136 you will see it change colour.
If you then select the triangle next to it made up of points 230, 127
and 133 you will see that the common line from 230 to 133 reverts to its
original colour and the outside of the two triangles remains blue, or whatever
colour you have set up on your machine.
Once you have selected all the triangles required, pull down the Contour
menu again, highlight the Edit Model option, and pick Delete selected triangles
and you will have achieved the end result.
Remember then to again pick the Select Independent triangles option to
turn it off and return your cursor to the normal pointer.
This option allows you to construct a polygon around the area where you
wish to remove triangles.
Only triangles
that are completely within the polygon will be selected.
To use this option, pull down the Contour Menu, followed by Edit Model,
and then pick Select Triangles by Polygon.
Then drag your cursor around to build the polygon you require, and press
the Enter key once finished.
The screen at left shows the Polygon, and the perimeter of the selected
triangles within it.
You will now see the perimeter of the triangles you have selected change
colour, and, providing you have got the polygon in the correct place; you can
then use the Delete Selected triangles Option.
3a. Insert Strings and remove Contours in areas
enclosed by the strings.
Before we start on this process there are a number of fundamental rules
that you must keep in mind if you intend to use strings to remove contours or
triangles
a. All strings MUST be defined in a String Folder named “BOUND”.
b. All strings MUST be closed i.e. they must start and end on the same
point
c . You can elect to delete the contours/triangles either Inside or
Outside of the closed string.
d. If you intend to use a string to delete contours/triangles Inside the
string, you should commence the String ID with the letter I e.g. In1, In2 etc..
e. If you intend to use a string to delete contours/triangles Outside
the string, you should commence the String ID with the letter ‘O” e.g. Out1,
Out2 etc.
Now you need to add in the strings, so pull down the Strings Menu, and
Select the Add option.
Type ‘bound’ in the folder name and press Tab or Enter to move to the
String Id field.
Enter a String ID of IN1 to indicate you wish to delete Inside the
string.
The points you need are; 203,236,230,231,127,128,130,133,136,137,203
Once you have entered the first string, Select Apply.
Now repeat the process to add another string with an ID of IN2 which is
made up of points; 239,237,204,208,210,212,213,214,239
At this point the screen at below should appear, with the boundaries
displayed. (If the triangles are in your way use the Modes Screen or F8 Key to
turn them off).
If you now turn
your contours on, (with the F7 key or the Modes Screen) the screen will appear
as below left.
Now pull down the Contour Menu, Select the
Boundaries Option, and select Contours.
A pop up window will scroll through the contours being processed, and
the screen will be redrawn as seen above right.
At this stage, you have removed the contours outside the area of
interest, so you can get a plot out showing what you need.
However, you MUST be aware that this method, while quick and effective
in terms of presentation plotting is not the ultimate method of removing the
unwanted parts of the model.
In fact, this method does not touch the underlying model at all, and if
you press the F8 key to display the triangles, you will see that the original
triangles still cover the areas where there is not supposed to be any data.
If you were to select the Option to Calculate Contours again, you would
again have contours where contours are not meant to be.
And, if you used this model for the calculation of Volumes, it is quite
possible that you might get a completely wrong answer as the model is
covering an area not intended to be part of the volume calculations.
So, why you ask do we have this method it doesn’t do everything needed?
The answer is because it is the fastest way for you to get the plot you
are looking for.
While in this example there is effectively no difference between the
time taken to remove contours and the time taken to remove triangles, on large
jobs the time taken for the triangle removal can be considerably longer.
So, if it is for purely cosmetic reasons that you wish to remove
contours from some areas of the job, this method is perfectly adequate, but if you
wish to use the job to calculate volumes, it is strongly recommended that you
use the Triangle method described below.
3b. Remove Triangles in Areas Enclosed by Strings
For this method, the procedure is identical to that you already been
through to remove contours, except that when you pull down the Contour Menu and
select Boundaries, this time you pick Triangles instead of the contours option
you picked previously.
I leave it for you to use the Triangle method by yourself.