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Chapter 4 Terrain model

 

This chapter shows you how to create a terrain model from the survey data. You will see how to display the terrain model in various ways.

 

The Plan window

Once the survey data has been converted into HighRoad format (see Chapter 3, Survey data) the points are displayed in the Plan window, initially shown as dots and a point number. Zoom, Shrink and Pan tools (and short-cuts) and Fit to window are available in the Plan window for faster and easier navigation.

 

Zoom

Choose Zoom from the Edit menu and the cursor changes to a magnifying glass which contains a plus (). Click the point of interest and the view will be magnified by a factor of 2. The point of interest will be in the centre of the window. As a short-cut, you can select Zoom using the Command () key on Macintosh or the Alt () key on Windows.

 

Shrink

Select Shrink and the cursor changes to a magnifying glass which contains a minus (). Click the point of interest and the view will be shrunk by a factor of 2. The point of interest will be in the centre of the window. As a short-cut, you can select Shrink by simultaneously using the Command () and Shift () keys on Macintosh or the Alt () and Shift () keys on Windows.

 

Pan

Select Pan from the Edit menu and the cursor will change to a hand (). Drag the view in the direction you want to move it. The view will be redrawn in the new position when you release the mouse button. As a short-cut, you can select Pan by using the Option () key on Macintosh and the right mouse button on Windows.

Fit to window

Select Fit to window from the View menu and HighRoad will choose the largest possible scale so that all the terrain points in a project can be seen in the window.

 

Feature strings

Natural and constructed features represented by points on the terrain model can be displayed in different ways by using feature strings. Features are defined by joining together the points on the terrain model which belong to that feature. HighRoad can automatically join feature points together based on a code associated with each point.

 

Natural features such as ridges and gullies, and man-made features such as drainage ditches and road shoulders can be modelled by defining them as breaklines. These are features which define the shape of the terrain. Triangles which form the terrain model cannot cross a breakline -- if the breakline is defined after the triangles are formed then any triangles which intersect the breakline will be changed.

 

Adding feature strings automatically

HighRoad will attempt to automatically join features during the conversion of a list of points or a list of data logger readings. As the points are processed, HighRoad will search the points for any which have a comment attached. When a point with a comment is found, the comment is compared with a library of predefined codes. If a definition already exists for a comment, then that definition will be used. If a match is not found HighRoad will ask whether you wish to add this code to the library. If you choose to add to the library, a dialog box as shown in Figure 4-1 will appear.

 

In the example in Figure 4-1, the comment associated with a point is TOP (representing top of bank) and it will be added to the end of the library. You can also specify the properties of this feature. In this example the feature will be shown with the symbol X at each point on the feature string, and the symbol will be 4 pixels in size. The points will be joined together with a 1 pixel thick line. This feature is a breakline. If the Breakline option is checked then any triangles which cross the breakline will be re-arranged.

 

Figure 4-1

 

If the option Join Points is not checked, the Pen Size and Closed options are not available. Choose Closed if a line is to be drawn from the last point, back to the first. This is useful for displaying a building, for example.

There are some special feature types which you can select from the pop-up menu at the bottom of the feature dialog box. The default condition is None. A Pegged line feature is a special feature type that allows the profile, cross sections and setting out data to be related to a pegged line. The pegged line should be approximately parallel to its control line. Use Volume boundary to measure volumes of an irregular site. Choose Cut-block for displaying cut-blocks in the 3D view. Use Wall to help visualise features on the 3D view. Link anchor is used automatically by HighRoad when intersections and cul-de-sacs are created. See Attaching a pavement to a feature, in Chapter 7, Typical sections for information about how to use this option in your projects. When you select one of the items from the pop-up menu, other conditions required for that option are forced. For example if you choose Volume boundary then the feature has to be joined, contourable and closed. These items are checked and made inactive so that they can not be changed.

You can use Next and Previous to look at other features already defined. Once you have defined the feature type, click OK, and this feature definition will be added to the library. A new feature will be added to the model and the list of points will be scanned in order and any others with the same code (TOP) will be added to this feature.

Note: It is important when doing a survey to ensure that you pick up points along a feature in order from one end to the other. The point numbers do not have to be consecutive, just in order.

Once all points have been scanned, the plan will be displayed with the features shown as you have specified.

 

Coding feature strings

When coding feature strings that HighRoad will insert automatically, you should follow certain conventions. You can use up to 12 alphabetical characters as a code for feature strings. If a particular job has more than one feature of a particular type you follow the alphabetical characters with a number. There is no space between the alphabetical characters and the number. For example following codes are valid:

Point# Code

1 TOP

2 TOE

3 TOP

4 TOE

5 DRN1

6 TOP

7 DRN1

8 TOE

9 DRN2

10 TOP

11 DRN2

These might represent the top and toe of a bank and two drains. HighRoad would search for the following codes in the library:

TOP

TOE

DRN

Points 1, 3, 6 and 10 would be joined to form the feature TOP. Points 2, 4, and 8 would be joined to form the feature TOE. Points 5 and 7 would be joined to form the first DRN feature, and points 9 and 11 would be joined to form the second DRN feature.

 

The survey points

When HighRoad converts the text file duplicate points, or those within 10 mm of each other, are made non-contourable. Some points are difficult to view at a small scale because they overlap. By changing the scale and scrolling you can view all points in the model and examine the correctness of the information at this stage. To assist you, various information about the points can be shown. Choose Show Point Info... from the Plan menu. A dialog box as shown in Figure 4-2 will appear.

 

Figure 4-2

 

You can choose to display a point marker to show its location, northing, easting and elevation and comments about the point. The points can be represented by a dot, a cross or no marker at all. If none of the items in the dialog box are selected then no information about the points will appear on the screen. You can also choose to hide non-contourable points. Check the box labelled Hide non-contourable points. When non-contourable points are hidden, they cannot be found by double-clicking on or near them.

Note: The Plan window will be blank if no information is displayed for each point.

 

Editing information about a point

You can change the following information about a point: elevation, comments and whether or not it is contourable. Double-click on the point you wish to change. A dialog box will appear, as shown in Figure 4-3, and you can make the relevant changes.

 

Figure 4-3

 

All points are marked as contourable unless they are on a non-contourable feature or the elevation is less than -900 metres. Before the triangulation is done you can make a point non-contourable and these points will not be considered during the triangulation or subsequent contouring. If you make a point not contourable, you will not be able to click on it when forming the outside edge. The dialog box also indicates whether a point forms part of a feature string. You can also edit the feature information. If a feature string is incorrect or you want to change it, double-click on any point belonging to that feature and the dialog box (as shown in Figure 4-3) will appear. Click Feature. A dialog box similar to that shown in Figure 4-1 previously will appear. Alternatively you can double-click on the feature, or click on the feature to highlight it and then choose Get feature info... from the Edit menu. You can change the properties of this feature using the usual editing techniques.

 

Defining the perimeter

To create a terrain model of the survey data you must first create a perimeter line enclosing the points to be contoured. Choose Join perimeter points... from the Plan menu.

 

Figure 4-4

A dialog box (as shown in Figure 4-4) will appear. You can choose to join the points manually or automatically.

 

Defining the perimeter manually

Select Manual. Click OK. The cursor will be shown as a cross when it is over the Plan window. Choose a point on the outside edge as a starting point and click on it. Move clockwise to the next point and click it. A line joining the two points will be drawn. Continue clockwise around the outside edge.

As you join the points you will find that some are very close together and it is difficult to distinguish one from the other. When this occurs choose Zoom from the View menu and click on or near the points you are interested. You may find the short-cuts for Zoom, Shrink and Pan useful here. Alternatively you can scroll so that the points in question are near the centre of the screen and then choose a smaller scale from the View menu to enlarge the view of these points. Try different scales as necessary to be able to correctly join the points together.

HighRoad will not allow you to join to a non-contourable point as part of the perimeter line. If you make a mistake, choose Undo from the Edit menu. When you have clicked on the last point in the outside edge, go to the point at which you first started. Click it again. This signals to HighRoad that the outside edge is completed.

 

Defining the perimeter automatically

Click Automatic. The dialog box (Figure 4-5) will ask you to enter the maximum distance between points on the perimeter and the minimum angle for triangles adjacent to the perimeter.

HighRoad will estimate the maximum distance for you. Click Estimate. Click OK. The estimate can be inappropriate, so you need to check the perimeter that HighRoad defines.

 

Figure 4-5

 

The minimum angle for triangles adjacent to the perimeter refers to the angle between the edge line and the internal triangle adjacent to the edge. If the angle between the edge line and the internal triangle is less than that specified, the edge line will follow the more concave path to avoid this narrow angle. This is illustrated in Figure 4-6. Set the angle to zero to consider distance only. If you wish to redo the triangulation with a different distance or angle, choose Rejoin perimeter points... from the Plan menu. Experiment with the different settings until you are satisfied with the result.

 

Figure 4-6

The terrain model

Once the outside edge is defined, HighRoad can create a terrain model of the survey data. Choose Contours... from the Plan menu. A dialog box will appear as shown in Figure 4-7. You can set the contour interval, the interval between major contours and the tension of the contours and choose to apply smoothing on screen. HighRoad will complete a triangulation of the data and then draw the contours on the screen at the specified intervals and tension.

 

Figure 4-7

 

You can change the scale and scroll up and across to view the terrain model. You can choose what information HighRoad will display about the terrain model. You can hide or show the triangulation, the contours and details about the points by selecting the relevant items in the Plan menu. You can also draw the contours at different intervals choose Contours... from the Plan menu. Choose Fit to Window from the View menu and all the points of the terrain model will be shown on the screen.

 

Making points non-contourable

Points can be made non-contourable after triangulation is done. The triangulation is adjusted after such a change. Points on the outside edge cannot be changed.

 

Adjusting the elevation of points

You can adjust the elevation of individual points or groups of points. Groups of points can be selected by shift-clicking the points -- additional points can be added to the group by shift-clicking on them. Points in the group can be removed by shift-clicking them. Points can also be selected by dragging a rectangle around thepoints to be selected. The selected points will be highlighted. Choose Adjust selected points... from Plan menu. The dialog box that appears (see Figure 4-8) allows you to alter all the elevations to the same value, or change them all by the same amount.

 

Figure 4-8

 

This option is useful when working with a rock stratum. If you know that rock in the area is generally 2 metres below the surface, you can duplicate the DTM to create a rock stratum at this depth. In some areas you may have more precise information such as from test holes. In these areas of the rock DTM, select the points in the vicinity of the test hole and adjust their elevations to suit rock depth in this area.

 

Adding new points to the terrain model

Individual points can be added to the terrain model. Choose New terrain point... from the Plan menu and a dialog box appears as shown in Figure 4-9. You can specify the plan location of a point by clicking at the location of the point or by entering its co-ordinates. The elevation of the point can be either a known elevation or can be calculated by HighRoad to be at ground level at that location. If you choose to have HighRoad calculate the ground level, and the point is outside the terrain model, a notice will be displayed and the point will not be added. Points outside the terrain model with a known elevation will be non-contourable. The default point number shown is the next number after the highest point number already used. You can use any number you wish, however it is recommended that you use a number which has not already been used in the current project. A list of points can be read in straight from a text file. The data must be in one of five formats:

* Point# Northing Easting Elevation [comment]

* Point# Easting Northing Elevation [comment]

* Geodimeter format

* DXF

* NTF

 

Figure 4-9

Points within the perimeter of the terrain model will be inserted into the model. The points will be added into the triangle into which they fall, or if exactly on a line between two triangles, they will be changed to four triangles. The triangulation in the immediate vicinity of the point will be adjusted if necessary. If there are existing breaklines in the vicinity they will be respected. If the points are of elevation below -900 metres they will be made non-contourable and not added to the triangulation. If they are outside the perimeter they will also be made non-contourable.

You can read in the additional list of points when a project is open and the terrain model has been created. Bring a Text window to the front. Choose Open Text File to open the list of points. Choose Convert from the Edit menu and the points will be processed and added to the active terrain model.

New features will be created with this process, if the new points have comments attached. If the comments do not match codes in the current feature library you will be asked whether to add the code to the library (just as would happen if creating the job from the start). If the features are breaklines, the terrain model will be adjusted accordingly.

Additional points can be added one at a time to a terrain model after it has been triangulated. Be sure not to put a point exactly over an existing point or triangle edge. Points outside the limits of the contourable model will be forced to be non-contourable. HighRoad will retriangulate the area in which a new point is added if it is a contourable point. Adding new points may change the shape of the terrain and it may require further work such as the creation of a breakline feature to ensure the model is correct.

 

Deleting points

You can delete points by selecting them and then choosing Clear from the Edit menu or by pressing the delete key. To select a point click on it. To select multiple points hold down the Shift key while clicking on points, or drag a rectangle around the points to be selected. If a point is on the perimeter line it cannot be deleted. To delete such a point you must first discard the triangulation and the perimeter line. This is done by choosing Rejoin Edge Points from the Plan menu.

 

Adding feature strings manually

You can add a feature string at any time after the contours have been formed by choosing New feature string... from the Plan menu. A dialog box as shown in Figure 4-10 will appear. If the option Join Points is not checked, the Pen Size and Closed options are not available. Choose Closed if a line is to be drawn from the last point, back to the first. This would be useful for a building, for example. If the Breakline option is checked then any triangles which cross the breakline will be rearranged. Once you have selected the options you require, click OK and then click on the points, in order, that make up the feature. You can undo any number of points. Double-click on the last point. If the feature is a breakline, the triangles will be redrawn so that no crossovers occur.

 

Figure 4-10

 

There are some special feature types which you can select from a pop-up menu at the bottom of the feature dialog box. The default condition is None. A pegged line feature is a special feature type that allows the profile, cross sections and setting out data to be related to a pegged line. The pegged line should be approximately parallel to its control line. Use Volume boundary to measure volumes of an irregular site. Choose Cut-block for displaying cut-blocks in the 3D view. Use Wall to help visualise features on the 3D view. When you select one of the items from the pop-up menu, other conditions required for that option are forced. For example if you choose Volume boundary then the feature will be has to be joined, contourable and closed. These items are checked and made inactive so that they can not be changed.

 

Editing a feature string

If a feature string is incorrect or you want to change it, double-click on any point belonging to that feature and the dialog box (as shown in Figure 4-3) will appear. Click Feature. A dialog box similar to that shown in Figure 4-1 will appear. You can change the properties of this feature using the usual editing techniques.

Feature strings can also be edited by clicking on the feature to select it. (A feature that is selected is highlighted by making it wider and patterned.) Once a feature string is selected you can edit it. Choose Get feature info... from the Edit menu (or use the keyboard short-cut i for Macintosh, Alt i for Windows). A dialog box similar to that shown in Figure 4-1 will appear. You can change the properties of this feature using the usual editing techniques. Alternatively, double-click on a feature and the feature dialog box similar to that shown in Figure 4-1 will appear. Use the usual editing techniques to change the properties of the feature.

 

Faster plan redraw

You can choose whether plan redrawing will be stopped when the mouse is clicked. Select Preferences... from the Edit menu. Check the box labelled Stop plan redraw on mouse click. This setting will be remembered by HighRoad. Once selected, plan redraw is stopped when the mouse is clicked. This is useful if you are zooming in on part of the plan. You may need to zoom in several times to get to the scale that you want. Instead of waiting for the plan to fully redraw each time, you can wait just long enough to see sufficient detail to know where you are, then choose Zoom again. As you click on the View menu the plan drawing will stop, allowing you to select Zoom again. (This also applies if you are using the Command () key on Macintosh or the Alt () key on Windows to zoom.) Be aware that the plan view may be incomplete if the mouse button is down at any time during plan redraw. Plan drawing does not stop under all conditions. The first time contours are drawn they also have to calculated. This cannot be interrupted. Subsequent redraws are much faster (providing sufficient memory was available to store the contours) and can be interrupted by a mouse click.

You can force an update of the plan view. If you interrupt the drawing of the plan view, you may be left with a partly completed plan. To force the Plan window to be redrawn, click on the size box in the lower right corner. The Plan window will be redrawn completely. You can choose not to display any mark at all for points. Choose Show Point Info... from the Plan menu and click on None under Point marker. This means that you do not have to wait for the dots to be drawn for points. This speeds up redraw noticeably on slower computers. In combination with redraw interruption this can speed your work considerably.

You can turn off items which are not needed for the current task. Select Hide Triangulation or Hide Features as appropriate. This will improve redraw speed. To speed up the contour redraw, choose a larger contour interval.

 

Adding another stratum

Note: This option is available only if you have the Extra DTM module. This module is included in HighRoad Pro and is optional in other models.

 

Another terrain model can be created by duplicating the ground model, offset by a fixed height. This is useful for modelling geological strata such as rock layers. To add this new stratum to a project, choose Duplicate DTM from the Edit menu when the Plan window is in front. The dialog box, as shown in Figure 4-11, will appear.

Set the depth to the new stratum, click OK and another terrain model representing the stratum will be created. The contours that appear will be on the surface of the stratum. This new stratum will appear in cross sections displayed on screen, or printed or plotted. The names of both strata will appear in the Active menu. Choose the active stratum (the one you want to work on) when the Plan window is in front.

Figure 4-11

 

You can show or hide contours independently for each layer. The menu item Show/Hide Contours will display the name of the active stratum. If the stratum you wish to enter is not parallel to the ground layer, you can change the elevation of individual points or groups of points. Groups of points can be selected by shift-clicking the points -- additional points can be added to the group by clicking on them. Points in the group can be removed by clicking them. The selected points will be highlighted. Choose Adjust selected points... from Plan menu. The dialog box that appears (see Figure 4-8) allows you to alter all the elevations to the same value, or change them all by the same amount.

 

Deleting the second DTM

You can delete the second stratum that you have created. The Plan window must be the front window and the second DTM must be active. Choose Clear from the Edit menu.

Note: Ensure that nothing is selected in the Plan window when you choose Clear. If something is selected then it will be deleted and not the DTM. For example if points are selected, choosing Clear will delete the selected points.

 

Constructing a road or pad

After you have completed your design, you can create a terrain model based on the finished surface of the new design after construction. This option is useful for calculating quantities more precisely when you have designed building pads and roads which overlap. It is also useful where you also need to design sewer or stormwater pipes. Design the road control line first, then construct the road (or pad). Choose Construct <Control line name> from the Plan menu. Now the terrain model shows the ground surface after construction. This would be useful for the design of pipes or intersecting roads or pads.

Note: Construct a road or pad only after you are sure of its position. Before you do this duplicate your original file otherwise you will lose it. Make sure the control line and its cross sections all remain totally within the terrain model before constructing.

When you construct the building pad the triangulation within the perimeter of the pad will change entirely. Some changes may also occur to triangles which adjoin the pad. The new triangles are formed according to the Voronoi diagram (see 24-1) and to suit new breaklines created along the edge of the pad and along the edges of links that make up the batter slopes. Occasionally, especially at corners, such a triangulation may not be ideal. You should examine the triangulation near the corners to verify that the triangle edges radiate from the corner. If not you may wish to insert additional breaklines radiating from the corner.

 

Transformations

You can change the co-ordinates of all points in a project by translation or rotation. When the Plan window is active, and no points are selected, choose Offset Entire Project... from the Plan menu. You will be presented with the dialog box shown in Figure 4-12.

Note: Keep in mind when rotating a project that all co-ordinates are rounded to the nearest millimetre. Multiple rotations can result in compounding of rounding errors of up to 1mm for each rotation. This can mean if you rotate a project and then rotate it back by the same angle, some co-ordinates may change by 1 or 2 millimetres. For most purposes this is far more precise by one or more orders of magnitude than the original data and so is of no practical consequence.

Figure 4-12

 

 

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