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

Universal Citation: LA Admin Code XXVII-1305

Current through Register Vol. 50, No. 9, September 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.

AUTHORITY NOTE: Promulgated in accordance with R.S. 50:171.

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