Data Management: Coverages

1
Data Management Coverages

• ARC commands for coverage maintenance creating,
  maintaining, modifying
• Generation generate
• Topology Maintenance build, clean
• Coordinate Adjustment projectdefine, project,
  transform, Adjust
• Registration register, rectify
• Joining mapjoin, Append, matchnode
• Modifying Dissolve, Clip, densifyarc, generalize

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Overview (repeat)

• The manipulation of coverages lies at the heart
  of ArcInfo-based GIS
• The methods or commands are numerous and can be
  classified in many ways
• There is always overlap, but basic groupings are
  
• Coverage Query techniques for querying existing
  coverages (see query.ppt)
• Coverage Maintenance creating, maintaining and
  modifying coverages (see covergages.ppt)
• Coverage Conversion converting from one GIS
  format or data model to another (see convert.ppt)
• Spatial Analysis manipulation of coverages to
  answer some research question or achieve some
  operational purpose (see analysis.ppt)
• Spatial analysis techniques may be used for
  coverage query anmd maintenace also
• We will discuss Query and Maintenance in the
  context of Workstation ArcInfo.
• query.ppt
• coverage.ppt
• ArcToolbox includes these in its Data Management
  component
• We will cover the Conversion and Spatial Analysis
  commands in the context of ArcToolbox,
• Conversion.ppt
• Analysis.ppt

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• Spatial Analysis
• Some of the spatial analysis methods,
  especially polygon overlay, can also be useful
  for coverage maintenance. In essence, you use
  one coverage to control or effect changes in
  another. These will be covered in a later
  lecture.
• Polygon Overlay (ARC)
• clip
• split
• erase
• update
• union
• intersect
• identity

• Coverage Maintenance
• (in this lecture)
• Coverage Generation (ARC)
• generate
• Topology Maintenance (ARC)
• build
• clean
• Coordinate Adjustment (ARC)
• projectdefine
• project
• transform
• Adjust
• Registration
• register
• rectify
• Joining coverages (ARC)
• mapjoin
• append and matchnode
• Modifying coverages (ARC)

no attribute merging
with attribute merging
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Coverage Generation

• You can generate a new coverage from any
  comma-delimited ascii file that contains a unique
  identification number (will become the ltcovergt-id
  variable, or user-id) and coordinate pairs for
  points, lines, or polygons.
• Prior to creating a coverage, determine if you
  would like single precision (coordinate accuracy
  to 3 decimals for geographic decimal degree) or
  double precision (coordinate accuracy to 6
  decimals)
• EXAMPLE FOR POINTS
• Arc precision double
• Arc generate airports
• Generate input airports.gen
• Generate points
• Generate quit
• Arc
• Remember to build topology after creation of a
  new coverage
• Arc build airports point

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Constructing Topology

• BUILD - creates or updates topology and the
  feature attribute table for a coverage
• BUILD ltcovergt POLY LINE POINT NODE
  ANNO.ltsubclassgt
• build airports point
• CLEAN - generates a coverage with correct
  polygon or arc-node topology. To do this, CLEAN
  edits and corrects geometric coordinate errors,
  assembles arcs into polygons and creates feature
  attribute information for each polygon or arc
  (i.e., creates a PAT or AAT).
• CLEAN ltin_covergt out_cover dangle_length
  fuzzy_tolerance POLY LINE
• (See topology in Lecture 1 Arc/INFO Basics)

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Adjusting Coverage Coordinates

• There are three basic commands that adjust
  coverage coordinate values PROJECT, ADJUST,
  and TRANSFORM
• PROJECT changes the coordinates from one map
  projection to another. PROJECT is the most
  mathematically accurate.
• ADJUST and TRANSFORM use corrections that youve
  specified through either links or tics.
• ADJUST - adjusts or rubbersheets a coverages
  features in either direction along the links
  (control points) in a separate link coverage or
  file. Links represent the from/to locations used
  in the adjustment. Adjust will localize
  coordinate changes.
• TRANSFORM - uses tics common to the coverage
  whose coordinates are to be transformed and an
  existing coverage to change the coordinates to
  match the output coverage. Transform scales,
  skews, rotates, and shifts all coordinates in a
  coverage but it does not perform rubber
  sheeting. Often used to transform a coverage
  from digitizer units to real-world coordinates.
• For georeferencing an image, use REGISTER and
  RECTIFY
• REGISTERinteractive application which performs
  homogeneous transformation for an image
• RECTIFY is required after REGISTER to convert the
  registered image from image coordinates to map
  coordinates.

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Changing Projections

• Before you begin you must know Current
  Projection of coverage
• Desired Projection of coverage
• FIVE COMPONENTS OF A PROJECTION
• Coordinate System US ALBERS, LAMBERT
• Datum NAD27, NAD83
• Spheroid CLARK 1866, WGS84, GRS90
• Units DD, METERS, FEET
• Parameters Depends on Coordinate System

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• Before you can project a coverage/grid or file to
  a new projection, you must know the current
  projection.
• Where would you find this information?
• Describe the coverage to see if projection
  shown
• Data Source -- metadata
• Best Guess--Trial and error
• Two commands to work with projections
• projectdefine -- define the projection
• project - actually projects the coverage from
  one coordinate system to another
• After you project data, do a BUILD on the file.

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Arc describe rain
Description of SINGLE precision coverage
rain FEATURE CLASSES
Number of Attribute Spatial
Feature Class Subclass Features data(bytes)
Index? Topology? ------------- --------
--------- ------------ ------- --------- ARCS
239 36 POLYGONS
111 28 Yes
SECONDARY FEATURES Tics
11 Arc
Segments 13462
TOLERANCES Fuzzy
0.303 V Dangle 0.001 V
COVERAGE BOUNDARY Xmin
2255128.700 Xmax
2622000.000 Ymin 6866000.000
Ymax 7098000.000
STATUS The coverage has not been
Edited since the last BUILD or CLEAN. NO
COORDINATE SYSTEM DEFINED
No projection information available
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Defining the Projection

• If the projection is not defined (not displayed
  with the describe command) you may elect to
  define the projection prior to projecting it to
  another coordinate system.
• PROJECTDEFINE prompts an interactive dialog for
  entering the projection information for a data
  set.
• Usage PROJECTDEFINE ltCOVER GRID FILE TINgt
  lttargetgt
• Arc projectdefine cover trails
• Define Projection
• Project projection geographic
• Project units dd
• Project datum NAD27
• Project parameters

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Second Example

• Arc projectdefine cover texas
• Define Projection
• Project projection Albers
• Project datum NAD27
• Project units meters
• Project spheroid clarke1866
• Project parameters
• 1st standard parallel 0 0 0.000 29 30 0.0
• 2nd standard parallel 0 0 0.000 45 30 0.0
• Central meridian 0 0 0.000 -96 0 0.0
• Latitude of projections origin 0 0 0.000 23
  0 0.0
• False easting (meters) 0.000 0.0
• False northing (meters) 0.000 0.0
• Project end

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PROJECTDEFINE PROJECTCOPY

• All projections, whether or not they have
  parameters, must have the word PARAMETERS entered
  to complete the projection definition.
• PROJECTDEFINE will not change the coordinates of
  the lttargetgt dataset. To project a dataset from
  one projection to another, you must use the Arc
  PROJECT command.
• For coverages, tins and grids, the projection
  information is stored as a PRJ file within their
  subdirectory. The projection information for a
  file is stored as filename.prj.
• The absence of a prj file results in the
  projection type being UNKNOWN.
• PROJECTCOPY allows you to copy the projection
  information from another coverage (essentially,
  it copies the .prj file) to save you entering all
  the info required by PROJECTDEFINE

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Projecting a Coverage

• PROJECT converts a geographic data set between
  two coordinate systems. PROJECT prompts an
  interactive dialog for entering the projection
  information for a data set.
• Usage PROJECT ltCOVER GRID FILEgt ltinputgt
  ltoutputgt projection_file
• Arc project cover trails trails_sp
• - will need to enter details at prompt
• OR
• Arc project cover trails trails_sp
  dd_state83.prj
• - requires a projection file called
  dd_state83.prj

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Sample without a projection file, with input
projection defined

• Arc project cover trails trails_sp
• 
  
• The INPUT projection has been
  defined
• Use OUTPUT to define the output projection and
  END to finish
• Project OUTPUT
• Project projection stateplane
• Project zone 5351
• Project datum NAD83
• Project units feet
• Project parameters
• Project end

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Sample without a projection file, with input
projection not defined

• Arc project cover trails trails_sp
• Use INPUT to define the input projection, OUTPUT
  to define the output projection, and END to
  finish
• Project INPUT
• Project projection geographic
• Project units dd
• Project datum NAD27
• Project parameters
• Project OUTPUT
• Project projection stateplane
• Project zone 5351
• Project datum NAD83
• Project units feet
• Project parameters
• Project end
• The parameters command must be included even if
  there are none to enter.

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Projection File - input projection not defined

• Any type of text file, saved with extension .prj
• Input
• projection albers
• datum NAD27
• spheroid clarke1866
• units meters
• parameters
• 29 30 0.0
• 45 30 0.0
• -96 0 0.0
• 23 0 0.0
• 0.0
• 0.0
• output
• projection stateplane
• zone 5351
• units feet
• datum nad83
• spheroid grs1980

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Georeferencing an Image

• REGISTER initiates an interactive program that
  allows you to georeference an image. The program
  provides views of the image and coverage data,
  and a menu from which the georeferencing
  operations are performed. From these windows, a
  series of links, or displacement vectors, are
  added that join image locations to map
  coordinates.
• Register identifies an appropriate
  transformation. This is saved in a "tiff world
  file" (.tfw) which is added to your workspace
• (note it's a homogeneous transformation, not a
  rubber sheeting)
• arc register plano.tif streets
• RECTIFY is used to convert the registered image
  from image coordinates to map coordinates.
  RECTIFY creates a new rotated, scaled and
  transformed image based upon the parameters in
  the world file. You must use rectify to apply
  this transformation permanently before it can be
  used in Arc/Info. This is not necessary to view
  it in ArcView
• arc rectify plano.tif planorec.tif

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DRAWING IMAGES

• The Arcplot command IMAGE draws a raster image or
  a group of images from an image catalog.
• IMAGE ltimage image_cataloggt band
• ltimage image_cataloggt - name of an image or
  image catalog. The image must be in a format
  supported by the IMAGE INTEGRATOR as shown in the
  following table.
• band - an integer value indicating the band to
  be displayed the default band is 1.
• Image catalogs are INFO data files that store the
  pathname and spatial extent of each image in the
  catalog.

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IMAGES SUPPORTED

• Image format Image naming
  convention
• TIFF no suffix required
• Sun Raster file no suffix required
• JPEG no suffix required
• Run-length Compressed (RLC) image.rlc
• ERDAS image.gisimage.lan
• IMAGINE image.img
• Band Interleaved by Line (BIL) image.bil
• Band Interleaved by Pixel (BIP) image.bip
• Band Sequential (BSQ) image.bsq
• GRASS Use GRASS naming conventions
• Arc Digitized Raster Graphics Use ADRG naming
  conventions
• Windows bitmap (BMP) image.bmp
• JFIF (JPEG compression) image.jpg
• Grid no suffix grids are directories

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Joining Adjacent Coverages

• Data in separate but adjacent map sheets may be
  joined into a larger, seamless, coverage.
• There are two commands to merge adjacent
  coverages into one.
• The APPEND command is used for coverages with
  either point topology or arc topology.
• MAPJOIN is recommended for coverages with polygon
  topology, or both polygon and arc topology.
• Generally, if MAPJOIN wont work, try APPEND
• Useful for files which come by county, for
  example TIGER files
• Files and their INFO tables must be clean and
  consistent across boundary
• May have to do ArcEdit on each first

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APPEND

• APPEND combines up to 500 coverages into one
  coverage.
• APPEND ltout_covergt NOTEST template_cover
  feature_class... feature_class NONE FEATURES
  TICS ALL
• NOTEST - Feature attribute tables are not
  appended.
• NONE FEATURES TICS ALL - specifies how
  tics and coverage features will be numbered in
  the ltout_covergt.
• NONE - neither Tic-IDs nor feature User-IDs will
  be modified. This is the default option.
• TICS - ID offsets will be calculated for tics.
• FEATURES - User-ID offsets will be calculated for
  the feature class(es) specified by the
  ltfeature_classesgt argument. Tic-IDs are not
  modified.
• ALL - ID offsets will be calculated for both tics
  and features.

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MAPJOIN

• MAPJOIN - combines up to 500 adjacent coverages
  containing polygon or networked features into one
  coverage and recreates topology.
• Mapjoin combines the APPEND and CLEAN processes
• Usage MAPJOIN ltout_covergt feature_class...featur
  e_class template_cover
• NONE FEATURES TICS ALL clip_cover
• Arc mapjoin soil poly features studyarea
• Enter coverages to be MAPJOINed (Type END or a
  blank line when done)
• 
  
• Enter the first coverage soil1
• Enter the second coverage soil2
• Enter the third coverage ltcrgt
• Done entering coverage names (Y/N)? y
• Do you wish to use the above files (Y/N)? y
• MAPJOINing files
• Arc

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Seamless Merging of Polygon Coverages

• One method to merge two (or more) geographically
  adjacent polygon coverages into one involves
  preparing coverages for edgematching, edgematch
  the coverages in ArcEdit, MAPJOIN the coverages,
  and then DISSOLVE the edge feature.
• Step 1 Prepare adjacent coverages for
  edgematching
• Remove coverage data overlap with SPLIT, CLIP or
  ERASE -
• Step 2 EDGEMATCH - Invokes an edge matching
  process in ArcEdit
• Step 3 Check item definitions and attribute
  values --
• definitions of items to the right of cover-id
  must match exactly, and attribute values must
  correspond (i.e. if soil type is 33 in polys that
  will join, the value must be 33 in both tables).
• Step 4 MAPJOIN in Arc - will be prompted for
  coverages to join
• Step 5 DISSOLVE the boundaries between the
  mapjoined coverages to create a seamless cover -
  aggregate based on attribute values
• Step 6 Reconstruct topology (BUILD or CLEAN)

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Merging of Point or Arc Coverages

• One method to merge two (or more) geographically
  adjacent point or line coverages into one
  seamless coverage involves the commands APPEND
  and MATCHNODE (arcs only)
• Step 1 Visually compare spatial data - edit, if
  needed.
• Step 2 Make sure item definitions and attribute
  values match
• Step 3 Perform APPEND - will be prompted for
  coverages to join
• Step 4 Perform MATCHNODE to snap nodes to nodes
  or nodes to points, and to extend dangling
  arcs to intersect other arcs.
• Step 5 Reconstruct topology

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COVERAGE OPERATION DISSOLVE

• DISSOLVE - eliminates arcs between adjacent
  polygons that contain equal values for a
  specified item.
• DISSOLVE ltin_covergt ltout_covergt ltdissolve_item
  ALLgt POLY LINE NET REGION.subclass
• You can specify any item from the ltin_covergt to
  be the ltdissolve_itemgt.

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Dissolve, pg 2

• Can be used to create a new polygon coverage
  based on variables contained within the file. For
  example, the Tiger/LINE file from the census
  bureau contains data for right and left polygons
  for each arc. From this file polygon topology
  can be built, and then items on which dissolve is
  possible includes census tract, census block,
  census block group, zip code, traffic analysis
  zones.
• While the input coverage may contain information
  concerning many feature attributes, the output
  coverage contains information only about the
  dissolve item.

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CLIP

• Strictly speaking, this is a Polygon Overlay
  spatial analysis command (and its covered in more
  detail in Analysis), but its commonly used in
  coverage maintenance, basically to limit the
  extent of one coverage to the area desired
• E.g. you have a highway map for Texas which you
  want to limit to D/FW only
• CLIP - extracts those features from an input
  coverage that overlap with a clip coverage. It
  extracts a portion of a coverage to create a new
  coverage.
• CLIP ltin_covergt ltclip_covergt ltout_covergt
  POLY LINE POINT NET LINK RAW
  fuzzy_tolerance
• Three covers specified in, clip and out.
• The ltclip_covergt must have polygon topology.
• Only the outermost boundaries in the ltclip_covergt
  are used interior polygons are ignored.
• CLIP uses the clip coverage as a cookie cutter
  only those input coverage features that are
  within the clip coverage are stored in the output
  coverage.
• Topology is built for the output coverage.

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DENSIFYARC

• DENSIFYARC - adds vertices to arcs in a coverage
  at a specified interval and alternately splits
  the arcs at each new vertex.
• DENSIFYARC ltin_covergt out_cover ltintervalgt
  VERTEX ARC
• ltintervalgt - the distance in coverage units which
  will separate new vertices. Existing vertices
  will be kept for each arc. DENSIFYARC will add
  new vertices to each arc by starting at the from
  node, traveling the ltintervalgt along the arc,
  adding a vertex, and so on. This process
  continues until the end of the arc is reached.
  Then the next arc is densified.
• VERTEX ARC - this specifies if vertices are
  added at each ltintervalgt or arcs are split at
  each interval.
• The vertex option will generate one arc with 5
  vertices
• The arc option generates 6 new arcs with no
  vertices.

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GENERALIZE

• GENERALIZE - reduces detail within coverage arcs
  a specified line simplification operator and
  tolerance.
• GENERALIZE ltin_covergt ltout_covergt
  ltweed_tolerancegt POINTREMOVE BENDSIMPLIFY
• ltweed_tolerancegt sets the tolerance in coverage
  units used to remove unwanted detail within arcs.
  
• POINTREMOVE BENDSIMPLIFY - specifies the line
  simplification operator.

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FUZZY TOLERANCE

• fuzzy_tolerance - nodes that are within the
  fuzzy_tolerance distance are merged into a clean
  junction.

before
after
fuzzy tolerance
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FUZZY TOLERANCE, pg 2

• Determining fuzzy tolerance if not given in the
  command line
• 1) Tolerance values are read from the existing
  coverage TOL file.
• 2) If no TOL file exists and the width of the BND
  is between 1 and 100, the tolerance is 0.002.
• 3) Otherwise, the tolerance is 1/10,000 of the
  width or height of the BND, whichever is greater.
• (BND is the file containing the extent of the
  coverage, thus BND is essentially the map width
  or height in map units.)
• A fuzzy tolerance value of 0 will not be accepted
  by most operations.
• Common fuzzy tolerances range from .001 to 1.