For each DTM, there are settings which control the display of the triangles. This is accessed from the Settings menu but may also be displayed at other times. The DTM Settings dialog box is
shown to the right. The Properties group shows the basic attributes that are used to display the lines representing the triangles.
When a triangular DTM is formed, there are often long, thin triangles around its edge. Normally, these triangles can be removed and the Boundary Filter options allow you to set filtering parameters for such triangles.
The by Percent check box and field allow you to specify the parameters by which long thin triangles can be removed. The value in the field is the minimum difference between the sum of the lengths of the two internal sides of a triangle and the length of the external side expressed as a percentage. In a situation where a triangle has an external side length of 50m and two internal side lengths of 40m and 10.5m, the triangle would be filtered since the sum of the internal sides is 50.5m which is only 1% longer than 50m.
The by Length check box and field allow you to specify the maximum length of the external sides of triangles and should be entered in metres.
The by External Feature check box allows you to remove external triangles that use three points from the same line feature.
Filtering only takes place if one or more of the check boxes are ticked. The algorithm will keep checking the data until it passes through all the triangles and no triangle is removed.
The display of DTMs allows you the option of using solid shading where colours are used represent different heights. The Shading group allows you to control this. The Layer field controls the layer on which the shading will be displayed and exported. The Interval field defines the interval used to calculate the coloured fills.
The first form of shading is to use one of the pre-defined colour schemes using the Pre-Defined radio button. The Colour Scheme field defines the colours that are used from lowest to highest. In its normal form, the interval is used to calculate the upper and lower bounds. If the lowest height is 100.1m and the interval has been set to 0.25m, the lower bound of the shading will be 100.0m. If the highest height is 120.1m with the same interval, the upper bound will be 120.25m. The first and last colours in the colour scheme name will be used to represent those heights. The middle colour in the scheme name will be used to represent the height in the middle of the range of heights. The colour of intermediate intervals will be calculated by linear interpolation of the red, green and blue components of the colours.
You can override the calculations of the colours by using the User Range check button. If ticked, the Minimum and Maximum fields are enabled and these values are the upper and lower bounds. This may be required if you are only interested in some of the height range, for instance the depths in a pond. It can also be used to match the height shading for two different models.