USING LITES2 AS A 3 DIMENSIONAL EDITOR

LITES2 AS A 2 DIMENSIONAL OR A 3 DIMENSIONAL EDITOR

In its default mode of operations, LITES2 is a two dimensional editor. This means that its geometrical treatment of features only relates to X and Y coordinates. Z information can be associated with individual points, but it is treated as an attribute of that point, not as a coordinate. Any manipulation of Z values is the responsibility of the operator, and is carried out by means of the EDIT ATTRIBUTE Z command.

By use of the (licensed) command ENABLE Z, LITES2 can be made to operate as a 3 dimensional editor. This means that Z is treated as a 3rd coordinate of all the points in the IFF files, and can be edited graphically in the same way as the X and Y coordinates. This graphical editing is carried out using the 3 dimensional nature of the LITES2 cursor.

THE 3 DIMENSIONAL CURSOR IN LITES2

The LITES2 cursor can be positioned in 3 dimensions. This is achieved by the use of the optional 3rd argument in the POSITION and ABSOLUTE commands. If this argument is not given then the height of the cursor is undefined.

Digitising devices (e_.g_. digitising tables, bitpads or mice) have no height information and only position the cursor in two dimensions (X and Y), however when LITES2 is using the KERN DSR photogrammetric plotter as an input device, it positions the cursor in three dimensions (X, Y and Z).

The height of the cursor can be ascertained at any time by the SHOW POSITION command. If ENABLE Z has been given then all three coordinates will be displayed; if the cursor height is undefined then a "?" is displayed in place of the Z coordinate. If Z is disabled (the default state) then the Z coordinate of the cursor is only displayed if it is set to a definite value.

These values are available in the system variables _$CURSX, _$CURSY and _$CURSZ. There is an additional variable _$CURSZ_EXIST which is true if the Z value of the cursor is defined.

POSITIONING THE CURSOR ON A FEATURE

When using LITES2 as a 2 dimensional editor and moving the cursor to a position defined by a feature (by FIND, SEARCH, FIRST, LAST, FRACTION etc) the height of the cursor is unaltered.

However when using LITES2 as a 3 dimensional editor, and moving the cursor to a position defined by a feature (by FIND, SEARCH, FIRST, LAST, FRACTION etc) the height of the cursor depends on the Z value of each point in the feature. If the cursor is positioned between two points, the Z value is interpolated in exactly the same way as the plan values are.

If, while the cursor is constrained on a feature, another feature is intersected, then the height of the cursor is determined by the height of the points in the original feature.

It is strongly recommended that when using LITES2 as a 3D editor, all existing data has proper 3D coordinates.

CONSTRUCTING NEW 3 DIMENSIONAL FEATURES.

Linear 3 dimensional features are simply created by positioning the LITES2 cursor and giving the START command. If the Z position is defined then this value will be added to the feature. To complete the feature the END command is given at the last point.

It should be noted that when operating in 3 dimensional mode, it is possible to have two adjacent points on a feature with the same plan position, as long as their heights are different. If such a feature is subsequently read into LITES2 when Z is disabled, then the second point will be lost.

If points are interpolated in a linear feature using the CURVE command, then the heights of the interpolated points are equally spaced between the heights of the master points. This is true whether Akima or McConalogue interpolation in X and Y is being used.

The heights of points generated by the CIRCLE, POLYGON, ARC, POLARC and RECTANGLE commands are determined by projecting the generated plan positions onto the plane through the master points. If there are only two master points (eg CIRCLE CENTRED) then the plane whose direction of maximum slope goes through these points is used. The affect of this is to generate features that have the expected shape on the map, not in 3 dimensional space.

Features of graphical types 2,3,4 and 5 (various types of circles and arcs) are constructed using appropriate START and END commands in the usual way, and a feature that is circular in plan is created.

Each of these features has a 3 dimensional plane associated with it, and this is used to determine the height of any point on it (e_.g_. this plane is used to position the cursor at the correct height during editing operations).

Symbols and texts take their height from the cursor when START is given. The height of the cursor at any second orienting or scaling point is ignored. Separate subtexts in composite texts can each have a different height.

EDITING 3 DIMENSIONAL FEATURES

Most of the 2 dimensional editing operations are available when using LITES2 as a 3 dimensional editor. The only exception to this is the FILTER command, which is not available when Z has been enabled.

There follows some comments on the manipulation of Z during various editing operations.

EDIT, EXTEND AND INSERT

These commands allow the Z value of a point to be altered (as well as its plan position) depending on the position of the cursor. The Z value can also be edited explicitly using the EDIT ATTRIBUTE Z command.

While using these commands the commands FORCE FLAT and FORCE SLOPE can be used to position the Z value of the cursor relative to the vector being edited. FORCE FLAT will return Z to the value it was at when the editing command was given; FORCE SLOPE will force Z to lie on the plane whose direction of maximum slope lies through the two points defining the vector being edited.

JOIN, TIE, MEND AND LOOP

These commands position the cursor between the two points being joined together. This applies to the Z coordinate in the same way as it does to X and Y. If the Z value of one point is undefined, then the Z value of the other point is used.

If the PROPAGATE command is given while JOINing or TIEing, the difference in Z between the selected point and the ends of the features is smoothed out along the same distance as the differences in plan position are.

CLOSE

CLOSE (NORMAL) positions the cursor to the X, Y and Z of the first point in the construction.

CLOSE SQUARE inserts a point on the line between the last digitised point and the cursor position, when the CLOSE SQUARE command is given. The height of this point is interpolated between the last digitised point and the cursor position, in the same way as the plan position. The cursor is finally positioned to the first point in the construction.

PART OPERATIONS, SPLIT, CLIP, INCLUDE AND BRIDGE

Editing operations that generate new points based on existing features linearly interpolate a Z value for these points in the same way as the X and Y are calculated. When circle arcs are clipped or split, the resulting features all lie on the same plane as the original feature.

ORIENT, TRANSFORM AND OFFSET

When the plan positions of features are altered using these commands the Z values of the points are not altered.

MOVE

When the plan positions of features are altered using this command, the Z values of all the points are altered by the difference in height between the point on the feature that the cursor was at when MOVE was given and the cursor height when END is given.

EDGEMATCH

While edgematching, heights are treated as in the primitive JOIN and TIE commands. As with the differences in plan position, the misclosure in Z is smoothed out back along both features if the propagating tolerance is greater than 0.0.

COMPOSITE TEXT MANIPULATION

When the PARAGRAPH command is given, all the resulting subtexts acquire the height of the first subtext.

When using the according to its position on the locating feature.