Louisiana Administrative Code › Title 43 - NATURAL RESOURCES › Part XXVII - State Lands › Subpart 1 - Land Information Mapping and Map Records System › Chapter 13 - Digital Mapping Requirements › Section XXVII-1305 - Digital Accuracy

Current through Register Vol. 50, No. 6, June 20, 2024
A. A number of
				  requirements must be addressed and complied with to ensure the accuracy of the
				  final digital product. These accuracy requirements are separate from those that
				  are considered throughout the preceding ground control, aerial photography and
				  analytic aerial triangulation phases of the map compilation process. Each of
				  the following digital accuracy requirements must be fully complied with to
				  ensure final product acceptability.
1. Grid
				  Control. Grid control refers to the establishment of coordinate grid lines and
				  pretargeted horizontal control points referenced to the Louisiana State Plane
				  Coordinate System. All coordinate grid lines and pretargeted horizontal control
				  points shall be established by direct keyboard entry of numeric coordinate
				  values carried to the nearest one hundredth of a foot (0.01') at final ground
				  scale. Manual digitization of grid line and horizontal control point locations
				  shall not be allowed.
2. Geographic
				  Registration. A minimum of four registration points shall be located in each of
				  the four corners of each manuscript map. All registration points shall be
				  established through direct keyboard entry of numeric coordinate values derived
				  from analytical aerial triangulation and carried to the nearest one hundredth
				  of a foot (0.01') at final ground scale. Manual digitization of registration
				  points shall not be allowed.
3.
				  Root Mean Square Error Tolerance. The Root Mean Square Error Tolerance (RMS)
				  defines the error incurred when predefined ties are used to register a map
				  during the digitizing process. The RMS error is an important tolerance because
				  it indicates, in part, the accuracy with which the digitizing technician
				  captures the locations of the registration points of a map in both the X and Y
				  directions. In order to preserve the spatial integrity of map features during
				  the automation process, it is extremely important to keep the RMS error as low
				  as possible when a map is registered on the digitizing tables. The limiting RMS
				  error for digital map products to be developed under these standards shall not
				  exceed five thousandths of an inch (0.005") at final map scale.
4. Fuzzy Tolerance. Fuzzy tolerance defines
				  the minimum distance separating arc or line segment coordinates, which is
				  limited to two thousandths of an inch (0.002") at final map scale (see
				  §1315 D, Appendix D, Figure 4).
5. Dangle Length Tolerance. Dangle length
				  tolerance defines the minimum length of a dangling arc or line segment, which
				  is limited to one tenth of an inch (0.10") at final map scale (see §1315 E, Appendix D, Figure 5).
6.
				  Digitizing Accuracy. Digitizing accuracy refers to the accuracy of a digitized
				  feature in relation to the same feature on the stereo model or original source
				  map. Careful, consistent and systematic digitizing combined with thorough
				  verification are essential to ensure satisfactory point, line and polygon
				  development during the digitizing process. In order to achieve the limiting
				  positional map accuracy requirements set forth within Chapter 3, the following
				  digitization tolerances should be closely adhered to during final map
				  compilation:
a. at least 90 percent of
				  well-defined planimetric features on the digital map should be within one
				  hundredth of an inch (0.01") of the centerline of that feature on the stereo
				  model or original source map when plotted at final map scale;
b. 100 percent of all well-defined
				  planimetric features should be plotted within two hundredths of an inch (0.02")
				  at final map scale. The one hundredth of an inch (0.01") nominal tolerance
				  interval is equivalent to a standard 0.010 plotter pen width. When a proof
				  hardcopy plot of the digital map is overlayed on the original base manuscript,
				  discrepancies will be seen as an open space between the plotted feature and the
				  original manuscript. In establishing criteria for accuracy, it is important to
				  consider the resources for storing statewide digital data. In order to
				  facilitate the most efficient use of computer storage, it is necessary to
				  encode only the minimum number of coordinate vertices needed to capture the
				  essence of a cartographic feature within the one hundredth of an inch (0.01")
				  digitization tolerance.
7. Topological Accuracy. All digital map
				  products should be topologically clean and free of errors. The topology of all
				  maps must be verified and free of overshoots, undershoots, slivers, open
				  polygons, unlabeled polygons, and unresolved line segment
				  intersections.
8. Attribute
				  Labeling Accuracy. After a map file is attributed, it should be checked for
				  accuracy, and all errors should be corrected. Testing for accuracy should be
				  accomplished by the creation of test plots with labels that can be placed over
				  the base map and checked for accuracy. All errors should then be corrected. The
				  resulting final labeling accuracy should be less than 0.3 percent, or three
				  errors in 1,000 labels. The error tolerance reflects the accuracy of the
				  digital labeling to the stereo model or source map.
9. Edge Matching Accuracy. Map features
				  should not extend beyond coverage boundaries. Line segments or arcs which
				  intersect the boundaries of a coverage area must be accurately edge matched
				  with the corresponding line segment in adjacent coverages. Computer edge
				  matching techniques ensure an exact match. In lieu of an exact match, line
				  segments or arcs must be matched to within one hundredth of an inch (0.01"),
				  centerline to centerline. Line segments or arcs must not extend beyond
				  (overshoot) or fall short of (undershoot) the coverage boundary.