Transcript Digital spatial data - CEProfs

Digital Spatial Data
Francisco Olivera, Ph.D., P.E.
Department of Civil Engineering
Texas A&M University
Definitions
Digital Spatial Datasets: Synthesis -- in electronic format -of geographic (map) and tabular (table) information.
Data structure: method used to organize and store digital
spatial datasets.
Data Types
Features
Point datasets
Line datasets
Polygon datasets
Surfaces
Grid datasets
TIN datasets
Images datasets
Networks
Simple dentritic
networks
Simple loop networks
Features
All points required to
define the feature
geometry have to be
stored as part of the
feature definition.
Features
Point datasets
One-to-one relation
between features in
the map and records
in the table.
Features
Line datasets
One-to-one relation
between features in
the map and records
in the table.
Features
Polygon datasets
One-to-one relation
between features in
the map and records
in the table.
Surfaces
Grid datasets
Surfaces
TIN datasets
Surfaces
Image datasets
Networks
Simple dentritic networks
Networks
Simple loop networks
Data Structures of Features
Topologic data structures:
Store (1) the geometry of the features, and (2) the spatial relationship
between connecting or adjacent features (i.e., topology) in tabular format.
Points do not coincide.
Lines are simple.
Polygons are simple and space-filling (i.e., no overlaps or empty spaces).
Shared polygon boundaries are stored only once.
Coverages have topologic data structures.
Cartographic data structures:
Stores the geometry of the features.
Points can coincide.
Lines can be complex.
Polygons can be complex, and not necessarily space-filling.
Shared polygon boundaries are stored as part of the definition of each of
the adjacent polygons.
Shapefiles have cartographic data structures.
Data Structure of Features
A line is an open sequence of
points in which the first and
last points are called nodes,
and the remaining
intermediate points are
called vertices.
Nodes
Vertices
Data Structure of Features
Complex lines
Simple lines
Data Structure of Features
Complex polygons
Simple polygons
Data Structure of Features
Not space-filling polygons
Space-filling polygons
Data Structure of Features
Line and polygon topology
Line
From-Node
To-Node
Right Polygon
1
B
A
III
I
2
D
A
I
III
3
B
D
I
II
4
D
C
III
II
5
C
B
III
II
5
B
Left Polygon
1
A
I
2
3
C
II
4
D
III
Data Structure of Surfaces
Grid datasets:
Cellular-based data structure composed of square cells of
equal size arranged in rows and columns.
Grid definition requires: (1) the coordinates of the upperleft corner, (2) the cell size, (3) the number of rows, (4)
the number of columns, and (5) the value at each cell.
Cells that do not store any value are called NODATA cells.
Number of rows
(x, y)
Number of columns
Cell size
Data Structure of Surfaces
Triangular Irregular Network (TIN) Datasets:
Dataset constructed by connecting points -- for which the
TIN parameter is known – forming triangles.
Triangle sides are constructed by connecting adjacent points
so that the minimum angle of each triangle is maximized.
Triangle sides cannot cross breaklines.
The TIN format is efficient to store data because the
resolution adjusts to the parameter spatial variability.
Data Structure of Surfaces
Triangular Irregular Network (TIN) Datasets
Data Structure of Surfaces
Image datasets:
ARC Digitized Raster Graphics (ADRG)
Windows bitmap images (BMP) [.bmp]
Multiband (BSQ, BIL and BIP) and single band images [.bsq, .bil and bip]
ERDAS [.lan and .gis]
ESRI Grid datasets
IMAGINE [.img]
IMPELL Bitmaps [.rlc]
Image catalogs
JPEG [.jpg]
MrSID [.sid]
National Image Transfer Format (NITF)
Sun rasterfiles [.rs, .ras and .sun]
Tag Image File Format (TIFF) [.tiff, .tif and .tff]
TIFF/LZW
Data Structure of Networks
Simple dentritic networks:
System of simple lines -- called links -- connected at their nodes.
All links point towards (or away-from) a given node called sink.
One-to-one relation between From-Node (or To-Node) and link.
A
C
B
1
2
D
3
4
E
5
F
Link
From-Node
To-Node
1
A
D
2
B
D
3
C
E
4
D
E
5
E
F
F is the network sink.
Data Structure of Networks
Simple loop networks:
System of simple lines -- called links -- connected at their nodes.
Links can point in either direction or in both directions.
A
B
5
C
6
1
10
J
K
F
7
G
11
3
2
D
8
4
12
H 9
I
E
Storing Datasets
Features
Coverages are stored partially in their own folder and partially in the
common INFO folder.
Shapefiles are stored in at least three files (with extensions .shp, .shx,
.dbf) and up to seven files (with extensions .sbx, .sbn, .ain and .aih).
Surfaces
Grid and TIN datasets are stored partially in their own folder and
partially in the common INFO folder.
Image datasets are stored in different ways depending on the image
format.
Networks
Simple dentritic and loop networks are stores as a line dataset of links,
a point dataset of nodes, and a topology file.
Storing Datasets
Info
Coverage
Structure of a folder
containing different types
digital spatial data.
Grid
TIN
Image.tif
Shapefile.shp
Shapefile.shx
Shapefile.dbf
Managing Datasets
Renaming
Always use ArcInfo or ArcView utilities to rename coverages,
shapefiles, grids and TINs because some information is internally stored
with the dataset name.
Images can be renamed using the operating system utilities.
Copying and Moving
Always use ArcInfo or ArcView utilities to copy and move coverages,
grids and TINs to make sure the information stored in the INFO folder
is included.
Shapefiles and images can be moved or copied using the operating
system utilities, making sure all the files are included.
Sharing Datasets
Interchange files
Coverages, grids and TINs are shared as interchange files.
An interchange file is a single file -- with extension E00 -- that includes all
information stored in the dataset folder and its share of information
contained in the INFO folder.
If a limit is set on the size of the interchange file, then several smaller files
(i.e., E00, E01, E02, …) are generated rather than one single file. This option
was common when storage media had limited capacity.
An interchange file is obtained by exporting a coverage, grid or TIN. In turn,
a coverage, grid or TIN is obtained by importing an interchange file.
Compressed (“zipped”) files
To make sure that all files are included, shapefiles and images can be shared
as compressed files.