Calculate Infill Lines

Use the Calculate Infill Lines option (UCEFILLGAPS GX) to calculate and fill in line segments where the gaps between survey lines or transects are larger than the project specifications.

 

Calculate Infill Lines dialog options

Line selection	Choose all or selected survey lines for processing. Script Parameter: UCEFILLGAPS.LINESEL
Nominal separation	Specify the nominal or survey design line separation. Script Parameter: UCEFILLGAPS.NOMSEP
Minimum segment length	The minimum line segment length to fill. Script Parameter: UCEFILLGAPS.MINSEGLEN
Recalculate distances?	The first time through this process two new channels are generated: Closest_Left & Closest_Right. At each survey point these values depict the closes points on the two adjacent lines. The left and right are determined by facing along the direction of the survey. Subsequent times through the same process, to save time, skip the recalculation of these channels by specifying "No". Script Parameter: UCEFILLGAPS.RECALC
Store which points in segment?	Choose "All" if you want to store every point of each segment in the database. Choose "First and Last Only" if you want to store only the first and last points of each segment in the database. Script Parameter: UCEFILLGAPS.WHICHPOINTS
Cultural Mask (optional)	Choose a PLY file to act as a cultural mask for the map. No line segments will be generated within the polygon(s) defined by this file. If this dialog field is left blank, no cultural mask is added. Script Parameter: UCEFILLGAPS.MASKPLYFILE
Split lines to extents?	Use the drop-down list to choose "Yes" to split lines at survey extents or choose "No". Select this option when you have collected the data in a single continuous line. Script Parameter: UCEFILLGAPS.SPLIT
Break lines within extents?	Use the drop-down list to choose "Yes" to break the lines within the survey extents or choose "No". Select this option when your survey lines have turns within the survey area. Script Parameter: UCEFILLGAPS.BRAKEWITHINPLY
Number of smoothing passes	Specify the number of smoothing passes for calculating the line heading . The default is 50 if the entry is blank. Used when “Break lines within extents” is selected. Script Parameter: UCEFILLGAPS.NUMPASS
New map?	Use the drop-down list to select "Create new map" to plot to a new map, "Current map" to plot to the current map, or "No map" to not plot. Script Parameter: UCEFILLGAPS.NEWMAP

Choose a PLY File (or leave blank to draw) dialog options

Use the Choose a PLY file (or leave blank to draw) option to select a polygon file to act as the extents for the Calculate Infill Lines. Note that, this dialog only appears if the (CSV) file, which defines the extents of the focused area, is not found.

Polygon for extents

Choose a (CSV or PLY) file that defines a polygon to act as the extents for the Calculate Infill Lines. No line segments will be generated outside the bounds of this polygon. If this dialog field is left blank, the user is prompted to interactively draw the polygon on the map.

Application Notes

Typically, Calculate Infill Lines (UCEFILLGAPS GX) is used after the original inspection of the survey lines or transects’ layout, and the Footprint Coverage or Survey Coverage tools. If the coverage does not meet the specifications, you can run this tool to create a list of in fill line segments, return to the site, and survey them to fill in the gaps.

Several channels are added to the survey database:

• Fillgaps_Heading: the calculated heading in degrees of the survey segment.
• Closest_Left and Closest_Right: the distance in survey units to the closest survey line on the left and right respectively.
• Flag_SepL and Flag_SepR:  indicates where the gap on the left or right exceeds the thresholds.

In addition, the tool creates a new database (SurveyDatabaseName_Gaps) with the coordinates of the proposed fill-in segments.

The best practice is to collect the data along near-parallel distinct lines; however, Calculate Infill Lines also supports meandering survey lines. If you have collected the data:

• as a single continuous survey line with turnarounds outside the extent’s polygon, select “Split lines to extents?". For the gap calculations, the original survey line will be split into separate lines where it intersects the extents polygon.
• with turnarounds within the extent’s polygon, select “Break lines within extents”. For the gap calculation, the original survey line will be split wherever there is significant deviation (>30 deg) in the line heading. Lines shorter than two times the minimum segment length, will be discarded.

For each data point, along a survey line, the algorithm searches for the closest points to the left and right residing on adjacent lines (split/broken lines if split/break lines option has been chosen). If the existing lines are greater than the nominal separation, fill-in segments are calculated to be located in between the existing lines.

The segments are numbered by the number of the survey line (split/broken lines if split/break lines option has been chosen) to the left of the gap. That is NewLineNumber+LeftLineNumber.x, where:

• NewLineNumber is a decade (10) over the sum of the largest absolute line number and range of line numbers.
• LeftLineNumber is the line number to the left of the gap.
• x is the segment index.

For example, if an input database has lines L101, L102, ... L1102 in the input database, then the NewLineNumber will be 10000, and the new segment lines will be numbered as, L10101, L10101.1, L10101.2, ... L11102, L11102.1 in the output Gaps database. The new segment lines are stored in a new output Gaps database named using the naming convention SurveyDatabaseName_Gaps.gdb.

In addition, if "Split lines to extents?" is selected, then a new output Split database is named using the naming convention input SurveyDatabaseName_Split.gdb. The Split database stores the intermediate information of all split and broken lines for your reference.

The Split database will store all the split lines starting with line L2000. Also, if "Break lines within extents?" has been chosen, then all the broken lines starting with line L3000 will also be stored in the Split database.

Coverage gaps can fall into three different categories:

1. Coverage gaps that are within a pre-defined limit for the project
2. Coverage gaps that are greater than a predefined limit for the project
3. Coverage gaps due to obstacles or inaccessible areas such as long fence lines, along buildings, under/near trees, wharfs etc.

Coverage gaps that are within a pre-defined limit for the project are defined as those areas where the across-track line separation or the long-track measurement intervals exceed the project design parameters but are less than the project’s maximum allowable limits for these parameters. For most projects, the total cumulative area where these acceptable gaps are present would be limited to 0.1% of the total area to be surveyed (i.e. 0.1 acre, or approximately 4325 square feet, per 100 acres surveyed), and would specifically exclude large coverage gaps due to inaccessible areas around trees, along fence lines, or other known features.

Coverage gaps that are greater than the project’s pre-defined limits are defined as gaps that the project team has decided will not be acceptable for the intended needs of the geophysical survey. The parameters that are used to define these limits are the maximum allowable across track line spacing and the maximum allowable along track measurement interval. Factors that affect these two parameters include survey costs, the likelihood that the smallest target objective may be present where these coverage gaps occur, and the level of risk associated with the smallest target objective. The IVS/GPO/SIT results should be used to help the project team in their decisions. It must be understood by the project team that higher costs will be associated in setting small maximum allowable across-track separations and small maximum allowable along-track separations. When evaluating a track plot for coverage gaps of this type, gaps due to obstacles as explained below are excluded. Coverage gaps that exceed the specified maxima for a project would require returning to those areas to be in filled.

Coverage gaps due to obstacles or inaccessible areas such as long fence lines, buildings, under/near trees, wharfs etc. are usually easily identified in the air photos and other survey/field notes and drawings. Gaps such as these are not included in coverage assessments above and may require special processes to arrive at a final disposition to the associated areas. As an example, one such process would be to use a mag and dig operation to clear these types of areas.

Acknowledgments

The following document has been used in the compilation of this Help file, and further information can be obtained directly from it: