EDGEMATCHING WITHIN LITES2

The EDGEMATCH command allows features on either side of a predefined line to be JOINed, TIEd or EXTENDed automatically on this line.
This section of the user manual explains in detail how this is achieved and how to use the command.

DEFINING A BASE TO EDGEMATCH TO

Before features can be EDGEMATCHed a base must be defined. This base is a vector of a linear feature. To define it, a feature is found; the cursor is moved to the required vector (first vertex, or between the two vertices) with the VERTEX, NEXT, PREVIOUS, FRACTION (etc) commands; finally the command BASE EDGE is given. Any previously defined edgematching base will have been overwritten.

Details of the current edgematching base can be seen by giving the SHOW BASE command.

CONTROLLING EDGEMATCHING

Default settings of things that control edgematching may need to be altered. These are:-


* TOLERANCE EDGE - for finding points within this distance of the line, and then within this distance of the projection of the aforementioned point on the line. The default is set to 1.5 sheet mms


* TOLERANCE PROPAGATE - any mismatch between edgematched features will be propagated this distance back along both features.
If no propagation is required (ie the mismatch is to be taken out on the first vector of each feature) then this value should be set to 0_.0. The default is 10 sheet mms.


* MATCH FSN - only features with the same FSN will be edgematched.
OFF by default.


* MATCH FC - only features with the same FC will be edgematched.
ON by default.


* MATCH MAP - only features within the same map will be edgematched.
ON by default.


* MATCH LAYER - only features within the same layer will be edgematched.
ON by default.


* MATCH PC - only features with the same process code will be edgematched.
OFF by default.


* MATCH AC - only features which have exactly matching AC types 2, 3, 4 and 5 will be edgematched.
OFF by default.

Details of the current settings can be seen with the SHOW TOLERANCE and SHOW MATCH commands.

Note that MATCH settings are used by the TIE and JOIN command, and that the TOLERANCE PROPAGATE setting is used by the PROPAGATE command.

INVOKING EDGEMATCHING

There are three commands to invoke edgematching - EDGEMATCH JOIN, EDGEMATCH TIE and EDGEMATCH EXTEND. These are based on the LITES2 JOIN, TIE and EXTEND commands.

LITES2 does not allow a feature to be JOINed (or TIEd) to itself. This means that EDGEMATCH JOIN will not produce closed features. To achieve this effect, it is necessary to use the EDGEMATCH TIE command first, to produce features whose ends are coincident, then EDGEMATCH JOIN will give the desired result.

WHAT EDGEMATCHING DOES

The program acts as follows (EDGEMATCH JOIN and EDGEMATCH TIE):- When there are no more features found in the SEARCH, the edgematch is complete.
If there were any features which were found in step 1, that were not ultimately matched with something, the user is given the chance of giving the REVIEW command. This runs a command file that:-

CRITERIA FOR ACCEPTING MATCHING FEATURES.

The criteria used to accept found features to match with the "searched for" feature are:-

EDGEMATCH EXTEND

EDGEMATCH EXTEND SEARCHes for the next end of a feature as with JOIN and TIE. The intersection of the last line segment of the feature and the baseline is calculated. The feature is then extended or truncated to the intersection point on the base line. The amount by which the feature may be extended is limited to three times the current edgematching tolerance.

REVIEW takes the user to those positions where no intersection with the baseline could be calculated. This may occur when:-