Forested Areas from DPW

COVERAGE NAME: botany/dpw_forest (MGE version: flhab1.dgn)


DOCUMENTATION REVISION: 8/16/94

DESCRIPTIVE NAME: Forested Areas of Aberdeen Proving Ground

STATUS: Completed.

DESCRIPTION: This coverage contains polygons representing the forested areas of
  Aberdeen Proving Ground in three categories: open area, tree mass and
  shrub mass.

GEOGRAPHIC EXTENT: Aberdeen Proving Ground

COVERAGE TYPE(S): Polygons

COVERAGE SIZE:
  Arcs: 4842
  Polygons: 3238
  Labels: 3237
  Tics: 4
  Annotations: 0
  File size: 4111 Kb

MAP PROJECTION: Universal Transverse Mercator (UTM)
                Zone 18
                Units:    Feet
                Spheroid: WGS84
                Datum:    WGS84

SOFTWARE/VERSION: Sun Arc/Info 7.0

COVERAGE CREATED: 7/14/94

COVERAGE DEVELOPER: GIS preparation: Joan Meyer, Jim Kuiper
                    Original digitizing: Directorate of Public Works, APG

COVERAGE MODIFICATIONS: None.

CONTACT:    Jim Kuiper
  Address:  Argonne National Laboratory, Building 900-C42 (EAD)
            9700 South Cass Avenue, Argonne, Illinois, 60439-4832
  Phone:    708/252-6206 (Office)   708/252-6413 (FAX)
  Internet: kuiper@spatial.ead.anl.gov

ORIGINAL SOURCE INFORMATION:
  Media: Intergraph DGN files
  Author/Agency: APG Directorate of Public Works (DPW).
  Date: Approx. Feb/Mar 1994, based on March 24 and 25, 1992 aerial photos.
  Scale: 1:600 in built up areas, 1:2400 over rest of coverage area.
  Projection: Universal Transverse Mercator (UTM), Zone 18, units in feet,
    WGS84 datum and ellipsoid.
  Geographic Control: Done by data supplier and DPW, but based on GPS
    system of control points and ortho-photography.
  Data Conversion: Data was received in Intergraph DGN format.  It was
    loaded into Arc/Info using the IGDSARC translation program.

ACCURACY ASSESSMENT:
  The original data was digitized at scales of 1:600 or 1:2,400 from 1992
  aerial photographs and should have good positional accuracy.  This data
  was stored as unconnected arcs representing CAD style vegetation symbols.

  During the processing of the data in Arc/Info, steps were taken to
  simplify the boundaries which were much too detailed and inefficient for
  effective use on the EIS project.  The final boundaries are a generalized
  version of the original data.  The degradation of accuracy was minimal.

  No ground truth data was available compare with the data.

ASSOCIATED COVERAGES: See the 'botany' section or directory.

ASSOCIATED FILES: None.

COMMENTS:
  See the processing log following this documentation for details on editing
  work.

ARC ATTRIBUTE FILE ITEMS (AAT): 
  IGDS-TYPE   ( 3  3 I) Original Intergraph TYPE.
  IGDS-LEVEL  ( 2  2 I) Original Intergraph LEVEL.
  IGDS-COLOR  ( 3  3 I) Original Intergraph COLOR.
  IGDS-STYLE  ( 1  1 I) Original Intergraph STYLE.
  IGDS-WEIGHT ( 2  2 I) Original Intergraph WEIGHT.
  CODE        ( 1  1 I) Boundary type.  See below.

  Code  Meaning
  ----  -------
    4   Shrub mass boundaries.
    5   Line added manually to close a gap.  Generally tree mass boundaries.
    6   Tree mass boundaries.

POLYGON ATTRIBUTE FILE ITEMS (PAT):
  CODE:    ( 1 1 I ) Indicates tree mass or shrub mass.  See below.

  Code  Meaning
  ----  -------
    2   Tree mass polygon.
    3   Shrub mass polygon.
    8   Enclosed area not a tree or shrub mass.

POINT ATTRIBUTE FILE ITEMS (PAT): None

ANNOTATIONS: None

PROCESSING LOG:

 1) Converted the DGN data to arc data using the dgn2arc command.  These files
    were input at 1:2,400 scale and were called 2lnda.dgn, 2lndb.dgn, ...
    2lndn.dgn.

 2) Cleaned each coverage using 7.5 for the weed and dangle tolerances and
    using the line option.  This removes points closer than the tolerance,
    connects lines within the tolerance, and deletes lines shorter than the
    tolerance.  It also inserts nodes where lines intersect.  Although this
    sounds severe, the effect was to convert the complex, unconnected set of
    small curved lines making up a vegetation boundary to a connected, more
    general version that still had most of the original shape.

 3) The separate coverages were appended into one data set.

 4) Used the dissolve command to combine lines having the same attributes.
    This greatly reduced the data volume without any loss of information.

 5) Using ArcEdit, line fragments less than 16 feet in length were deleted.
    Gaps in boundaries were snapped together with a maximum snapping distance
    of 22 feet.  This was done by sections to observe the results.  Additional
    gaps were closed by hand using a 30 foot maximum distance.

 6) Some double lines, apparently from digitizing a boundary more than once,
    were deleted.

 7) The dissolve command from step 4 was repeated.

 8) The clean command from step 2 was repeated, but using a 0.1 foot tolerance,
    and the poly option.  Clean has no effect on data larger than the
    tolerance, so this step essentially made sure there were no intersections
    and created polygon topology.

 9) The createlabels command was used to insert label points into the polygons
    so polygon attributes could be attached.

10) Build was used to restore polygon topology after addition of label points.

11) A code item was added to the polygon attribute table.

12) Slivers, or tiny polygons in small boundary overlaps were removed along
    with their label points.  This work was done in steps with the build
    and labelerrors commands to check for mistakes.

13) Boundaries were splined with a grain tolerance of 30 feet to remove
    spikes left as an artifact of the original data.

14) Clean was run with 0.001 tolerances and the poly option.

15) Final polygon topology cleanup again included createlabels, dangle editing
    labelerrors checks, and step 16 below.

16) The NW boundary had unclosed vegetation polygons at the edge of the data
    extent.  These were closed with straight lines.  The added lines were
    given a separate code to identify them.  Also there were a few linear
    vegetation boundaries.  For these, a parallel line was added a small
    distance away to make a closed polygon.

17) Based on the codes on the original boundary lines, the polygons were
    attributed with a code of 2 for tree masses and 3 for shrub masses.
    Some areas represented clearings, but were enclosed polygons.  These
    were given a code of 8.  Shrub masses were very infrequent and make up
    little of the data set.