Data acquisition and integration Section 2

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Data acquisition and integrationSection 2

• Geospatial Analysis and Modeling
• Lecture notes
• Helena Mitasova, NCSU MEAS

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Outline

• geospatial data models raster, vector
• raster-vector conversions and resampling
• geospatial formats and conversions
• data repositories, interpreting metadata

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Geospatial data models raster

• continuous elevation, precipitation

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Geospatial data models raster

• continuous elevation, precipitation
  discrete land use, roads

5 developed
1 water
3 herbaceous
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2D raster data model

• header matrix of values (INT, FP, DP)
• continuous field value assigned to a grid point
• discrete object cat value assigned to pixel
  (area)
• imagery - several bands

Speed limit
Elevations
north 225720 south 223370 east 639900 west
637590 rows 235 cols 231 117.979 117.892
117.964 118.207 118.516 120.567 120.565 120.782
121.625 122.414 123.598 124.359 124.614 124.733
124.934 124.775 125.009 124.972 125.412 125.908
north 225720 south 223370 east 639900 west
637590 rows 235 cols 231 5 5 5 25 25 25 5 5 5 5
5 5 5 5 5 5 5 5 25 5 5 5 5 5 35 35 35 5 5 5 5 5
5 5 5 5 5 5 5 5 5 5 45 45 45 45 45 45 25 25 25
25 25 25 5 5 5 5 25 25 25 5 5 5 5 5 5 5 5 5 5 5
5 5 5
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2D raster data model for volumes

• multiple surfaces (set of 2D raster layers) can
  be used to represent soil horizons or geological
  layers
• combined representation
• continuous (horizontally)
• discrete (vertically)

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3D raster data model
org. carbon

• header 3D matrix of values
• vertical scale is usually much finer than
  horizontal
• mostly used for 3D continuous representation
  wf(x,y,z)

north 225720 south 223370 east 639900 west
637590 top 130 bottom 20
rows 235 cols 231 levels10
soil pH
contribution of real-world 3D data (point
samples, layers, volumes) from NC to the dataset
will be welcome
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Raster data - changing resolution

• Continuous data - reinterpolation

30m to 10m elevation

Nearest neighbor
Spline, bicubic polynomial
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Raster data - changing resolution

• 
  Discrete data -resampling

30m to 10m elevation
geology
Felsic Mica Quartzite Quartz diorite Metam
granite Amphibolite
Nearest neighbor
Spline, bicubic polynomial
interpolation creates categories that do not exist
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Raster increasing resolution
10m
10m
elevation 30m
nearest neighbor slope in the center cell is
zero!
interpolation 10m new image
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Raster increasing resolution
10m
10m
elevation 30m
nearest neighbor slope in the center cell is
zero!
interpolation 10m new image
geology 30m
nearest neighbor 10m
interpolation 10m
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Raster increasing resolution
20m
elevation 30m
nearest neighbor 20m, not all flats are square
interpolation 20m no problem similar to 30m to
10m
20m
geology 30m
nearest neighbor 20m area for each class may
change
but do not use interpolation !
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Raster decreasing resolution
nearest neighbor 30m 20m
elevation 10m
For some applications average, min or max may be
more appropriate, see also nearest neighbor
operations
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Raster decreasing resolution
nearest neighbor 30m 20m
elevation 10m
soilsID min or max will work but not average
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Geospatial data models vector

• Discrete streets, streams, geodetic points,
  census blocks

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Geospatial data models vector

• Discrete streets, streams, geodetic points,
  census blocks

Continuous isolines, points
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Geospatial data models vector

• vector data model - geometry
• x,y,(z) points representing points, lines,
  areas
• topology nodes, vertices, centroids, line,
  polyline, boundary, polygon
• 3D vector data face, kernel volume

areas
points, lines
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Vector data geometry attributes

• points, lines and areas are abstract
  representations of complex features (firestation
  point, road centerline, ...)
• attributes are stored in data management systems

geometry
633649.29 221412.94 1 628787.13 223961.62
2 629900.71 222915.80 3
L 9 1 630206.53 239151.59 629068.26
238374.22 .
B 10 641635.38 226175.44 641626.92
226020.09 .....
C 1 1 642246.66 225317.27 1 1

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Vector data geometry attributes

• points, lines and areas are abstract
  representations of complex features (firestation
  point, road centerline, ...)
• attributes are stored in data management systems

geometry
attributes
633649.29 221412.94 1 628787.13 223961.62
2 629900.71 222915.80 3
Cat ID LABEL LOCATION CITY MUN_COUNT PUMPER
PUMPER_TAN TANKER 21 0 RFD 20 1721 Trailwood
Dr Raleigh M 1 0 0....
L 9 1 630206.53 239151.59 629068.26
238374.22 .
catMAJORRDS_ROAD_NAMEMULTILANEPROPYEAR OBJECT
IDSHAPE_LEN 11NC-50no014825.369405
B 10 641635.38 226175.44 641626.92
226020.09 .....
Cat OBJECTID BLOCK_ BLOCK_IDBLOCKNUM TOTAL_PO
P POP_1RACE WHITE_ONLY BLACK_ONLYAMIND_ONLYAS
IAN_ONLYHWPAC_ONLYOTHER_ONLY
POP_2RACESHISPANICMALEFEMALEP_UNDER_5.......
. 18311783118831173718305350130084444410
300 00525191 ...
C 1 1 642246.66 225317.27 1 1

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Geospatial data models 3D vector

• 3D vector data (x,y,z) points, lines, areas and
  volumes
• volumes face, kernel volume
• extrude from footprint by given elevation
• full 3D model (CAD, Sketchup)

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Geospatial data models 3D vector

• Entire city - buildings extruded from
• footprints using height from associated
• database and stored as 3D vector data

Full 3D model with draped texture created in
Sketchup
See 3D NCSU in Google Earth - http//delta.ncsu.ed
u/about/research_initiatives/3d_ole/google_sketchu
p/
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Vector to vector data conversions

• polygons to points centroids or line vertices

Data geometry is not modified subset is selected
and stored in a different data structure
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Vector to vector data conversions

• polygons to lines (boundaries)

Data geometry is not modified subset is selected
and stored in a different data structure Topology
building is required for conversions point to
line, line to polygon
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Vector to vector data conversions

• Generalization (downscaling) - geometry is
  simplified
• roads, streams, contours, building footprints,
  urban areas,coastlines
• line to simplified line
• polygon (building footprint, urban area) to point
  symbol

Both data geometry and type can be
modified Needs to be considered when combining
local, state and national scale data Streams
12000 local, 124000 topomap, 11mil national
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Conversions between data models

• Vector to Raster
• Raster to Vector

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Vector -gt Raster conversions

• continuous interpolation, covered in separate
  lecture
• discrete nearest neighbor

Streets to speed limit 30m resolution raster map,
null replaced by 5
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Vector -gt Raster conversions

• continuous interpolation, binning
• discrete nearest neighbor
• areas attribute value applies to the entire
  polygon only complete polygons can be converted
  to be fully valid

Streets to speed limit raster map, null replaced
by 5
Census blocks to population 10m and 30m
resolution
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Raster-gtVector data conversions

• Continuous data sampling points

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Raster-gtVector data conversions

• Continuous data sampling points, isolines

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Raster-gtVector data conversions

• Discrete data points center of grid cell
• lines, polygon border lines connected grid cell
  centers
• thinning and smoothing is often performed for
  lines

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Raster -gt Vector conversions

• areas boundary, centroid, requires building
  topology
• connects points on grid cell boundary

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Common geospatial data formats

• Raster ?
• Vector ?

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Common geospatial data formats

• Raster
• GIS software ascii and binary - ArcGRID, GRASS,
  SURFER, ...
• Imagery MrSID, GeoTIFF, BIN, USGS DOQ, JPEG2000,
  ERDAS
• Graphics GIF, JPG,PNG, Bitmap, Pixmap
• HDF, NetCDF
• Vector
• KML, Shape, ArcSDE, GML, MapInfo, TIGER, PostGIS,
  OracleSpatial

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Geospatial data format conversion

• properties of the format are now stored with data
  automated format recognition and conversion
• Geospatial Data Abstraction Library (GDAL/OGR)
• gdal.osgeo.org
• given format -gt single abstract model -gt new
  format
• includes commandline utilities for data
  processing
• Related PROJ library provides coordinate system
  transformations

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Data repositories

• Major web geospatial data repositories
• http//skagit.meas.ncsu.edu/helena/classwork/hon2
  97webgis.html
• Explore CLICK, SRTMV4, LDART, NCFlood

Metadata Identification_Information
Data_Quality_Information Spatial_Data_Organi
zation_Information Spatial_Reference_Informa
tion Entity_and_Attribute_Information
Distribution_Information Metadata_Reference_
Information see example http//skagit.meas.ncsu.
edu/helena/grasswork/grassbookdat07/ncexternal/NC
LD_landuse2001meta.html
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Summary and References

• Data models raster / vector, continuous /
  discrete
• Chang Ch. 3,4,5, Neteler Ch. 2.1, 4.1.1 and 4.2.1
• Raster-vector conversions and resampling
• Chang 5.5, Neteler Ch 5.3,6.7
• Geospatial data formats, conversions
• Chang Ch 3,4,5.2-4, Neteler Ch. 4
• Data repositories