The Ultra Pre-processor has a number of road pack optimization options. These are set in the Optimization box at the bottom of the Configuration dialog box:
These options filter out disconnected roads to avoid spurious results, and intermediate (mid) nodes to save disk space.
Orphan Road Segments
Orphan road segments are relatively short sections of road network which do not connect to the main road network. Examples include tracks which are only connected by foot paths, and alleys in pedestrianized town centers.
Here is a vector depiction of the OpenStreetMap data in central York (UK). Most of the roads are pedestrianized (magenta). But the cyan road is tagged as "service", i.e. an alley. Although they are slow and low priority, alleys are routable by road vehicles whilst pedestrianized roads are not. Hence this is an orphan road segment.
The filter option only applies to orphan road sections that do not have any road junctions. By default, all orphan road segments shorter than 1 mile (1.6km) are filtered out. Change the maximum distance that will be filtered out, or clear the check box if you wish to keep all orphan road segments.
The road network is defined in terms of 'nodes'. These are points with coordinates. Intermediate ("mid") nodes are those which are not junctions. These nodes are not used in the routing logic, but they are used to draw a completed route on the Quality Control (QC) displays. They are also used when matching start/end points with the road network. This matching process will start (or end) the route from the closest intermediate node.
Removing intermediate nodes will reduce the disk size of the indexes included in a road pack, but it does not meaningfully reduce the memory requirements. Although there is a theoretical improvement in speed, this will be negligible.
Intermediate nodes are removed if the sum of two old links (to the nodes on either side) is shorter than a specific distance. Set this distance by setting the Prune mid-nodes where the new link is less than distance. The default for this maximum distance is 0.006 miles (10metres). This node is then only removed if the resulting deflection is less than the degrees deflection value. The default is 30 degrees. This avoids the new road link cutting across a short corner in the quality control display. The following diagram visualizes these constraints for a road segment ABC where point B is being considered for removal: