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Rasters and Surfaces

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Stretch Symbolization pulls the values across a colour range. ... Each Symbolization dialog allows you to pick the background and NoData colours. ... – PowerPoint PPT presentation

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Title: Rasters and Surfaces


1
Lecture 6
  • Rasters and Surfaces

2
Review of Vector GIS capabilities
  • Vector data models coverages, geodatabases
  • Inputting data
  • Editing spatial data in ArcEdit and ArcMap
  • Data management
  • Outputting data
  • Displaying data and presentation
  • Spatial analysis
  • Network Analysis

3
This Lecture
  • Rasters / GRIDs
  • Surfaces / TINs
  • 3D - fly-throughs

4
Raster Data
  • Pixel by Pixel data forms. Each is a Z Value for
    a particular x,y position in the file.
  • Can look at lots of formats.
  • Most usually held in ArcInfo in GRID format.
  • This format allows for Raster analysis.

2500 2502 2504 2506 2549 2501 2504 2506 2548 2500
2505 2505 2548 2549 2505 2505
5
Raster Data
  • Can hold height information as the values, or
    categories of e.g. land use.
  • Can be a single band, or a composite image of
    several bands, three of which you show as
    red/green/blue.
  • To work with other Coverages/Feature Classes each
    needs registering and a coordinate system adding.
  • However, you can use them with undefined Feature
    Classes as simple x,y coordinates.

6
Making Rasters Importing to ArcMap
  • Just open TIFF or JPEG image files.
  • Import from Coverages.
  • Import from Digital Elevation Models (DEMs) and
    other formats.
  • ASCII format common for exchanging data

7
Pyramids
  • Pyramids are a way of storing Rasters, so that
    the resolution shown changes with the viewing
    scale.
  • I.e. When you see more of the map spatially, you
    see less of the detail. Detail you wouldnt have
    seen anyway because of the screen resolution
    isnt shown.
  • This speeds up drawing.
  • When importing data, youre asked if you want to
    generate this.
  • If you later want to generate them toolbox
    Data Management gt Raster

8
Making Rasters Registering
  • Register ltimagegt coverage command in Arc.
  • Allows you to pick places on an image and link
    them to a Feature Class or x,y coordinates if the
    latter absent.
  • Interactive.

Creates a World file (.w) containing the
transformations needed
9
Making Rasters Projection
  • A Raster must also have a defined coordinate
    system.
  • You can define this in ArcCatalog.
  • Right-click on the file and select its
    Properties.
  • The process is then the same as setting up a
    Feature Dataset Spatial Reference.
  • NB Remember not to move image files outside of
    ArcCatalog once the registration and projection
    are defined.

10
Using Rasters Digitising
  • You can use Rasters in the same way as any other
    dataset, though the editing is limited.
  • One use is in Heads-up Digitizing, i.e.
    traditional tracing of photos to give Vectors.
  • E.g. Aerial Photos to Road Arcs.

11
Joining multiple input rasters Mosaic
  • Merge adjacent tiles into one larger raster
    dataset
  • Works best for continuous data e.g elevation

12
Symbolizing rasters
  • By default, rasters are drawn in shades of grey
  • Open Layer Properties and select Symbology tab
  • Three symbology methods
  • Stretched
  • Classified
  • Unique Values (lt512 unique cell values)

13
Using Rasters As Information
  • Stretch Symbolization pulls the values across a
    colour range.
  • No explicit colour-value relationship.
  • A variety of algorithms.

14
Using Rasters As Information
  • Classified Symbolization gives specific number
    ranges a specific colour.
  • No smooth transitions.

15
Using Rasters As Information
  • For multiband images, you can pick which colour
    is used for each band.

16
Using Rasters As Information
  • You can also pick the bands in Tools gt Options.
  • Each Symbolization dialog allows you to pick the
    background and NoData colours.
  • By default these are transparent.
  • With lt 24 levels you can symbolize by Uniques.

17
Other effects
  • Effects Toolbar
  • Adjust
  • Contrast
  • Brightness
  • Transparency
  • But be careful if you have more than one raster

18
Raster Calculator
Apply weights to rasters and combine using Raster
Calculator
19
Using Rasters 3D Raster Analysis
  • 3D datasets are known as Raster Surfaces.
  • Rasters can be used to store Surfaces (i.e. each
    pixel value is a height).
  • Of course, height need not be literal height
    it could be the amount of some variable.
  • There are a suite of analysis tools for this e.g.
  • Cut and Fill
  • Viewshed
  • Aspect
  • Slope

20
Cut and Fill Tool
  • Takes in a before and after raster.
  • If the first raster has had material removed from
    some areas, and shifted to other.
  • Results
  • Raster Coverage of changes.
  • Table of volumes.
  • Polygon Coverage showing changed regions.

21
Aspect
  • Slope direction or the compass direction a hill
    faces
  • Flat areas having no downslope direction are
    given a value of -1
  • Why use the Aspect function?
  • Find all north-facing slopes on a mountain as
    part of a search for the best slopes for ski
    runs.
  • Calculate the solar illumination for each
    location in a region as part of a study to
    determine the diversity of life at each site.
  • Find all southerly slopes in a mountainous region
    to identify locations where the snow is likely to
    melt first as part of a study to identify those
    residential locations likely to be hit by runoff
    first.
  • Identify areas of flat land to find an area for a
    plane to land in an emergency.

22
Slope
  • Most frequently run on an elevation dataset
  • Steeper slopes are shaded red on the output slope
    raster.
  • The function can also be used with other types of
    continuous data, such as population, to identify
    sharp changes in value.

23
Viewshed Tool
  • What can be see from? sometimes called
    Visibility calculations.
  • Can we see this new dam from a pleasure spot?
  • Can we see a road bend from the top of a hilly
    road?
  • Can we monitor the whole of a political march
    using this set of CCTV cameras?
  • Where will be damaged by a nuclear flash at this
    point?

24
Visibility Tool
  • Allows you to enter
  • 1 observer positions as a Point Coverage.
  • A vertical and horizontal view angle for each.
  • Offset (height above the surface)
  • See help for more details
  • Results.
  • Either a raster or Polygon file containing areas
    that can be seen from the observers without
    obstruction.
  • Tables containing either the number of observers
    that can see a point (frequency) or (for lt16
    observers) a list of which observers can see
    where.
  • Obviously a very computationally intensive
    process that results in large results files.

25
3D Vectors
  • There are some operations that are much easier
    with 3D Vector data.
  • Triangulated Irregular Networks (TINs) store
    Surfaces as 3D Vectors. Each line represents a
    slope breakpoint.
  • Note again that while the Z direction (up) is
    usually height, it could be some other variable.

26
Making TINs Importing
  • Raster to Tin
  • Massive Job, Very slow.

The height difference within which a Vector for a
location must fall when compared with the GRID.
Automatically given height conversion factor e.g.
feet to meters.
27
Making TINs
  • From GRID goes through putting lines between
    high points and testing the z difference against
    the raster, then adds more lines/points where
    needed.

GRID
Both
TIN
28
Using TINs As Information
Elevation
Aspect
  • TINs have three associated Attributes Slope,
    Elevation and Aspect.
  • You can shade on any of these.

Slope
29
Using TINs As Smooth Relief Shading
  • Place your DEM GRID (or other data) above your
    Elevation shaded TIN.
  • Use the Effects Toolbar Transparency Tool to set
    the GRID to 70 transparency.

DEM
TIN
Overlay
30
Using TINs Volume Analysis
  • TINs can be used with the Volume Surface Tool to
    calculate the volume of a surface from some base
    z value upwards.

31
Tools for Rasters and TINs
  • The Contour Tool will turn Rasters or TINs into
    contour Polygon Feature Classes.
  • In addition, there are conversion tools to
    convert Rasters and TINs into Polygon files, and
    vice versa.
  • This is one way to get from an image of e.g. a
    forest, to forest boundaries.
  • However, the conversions to Polygons tend to give
    blocky results because of the square edges of the
    pixels. This isnt the case with the Contour
    Wizard.

32
ArcScene
  • Much of the 3D functionality of ArcMap stuff
    for doing real 3D with tilted landscapes,
    animation and export to 3D formats.

33
Extruding and Baseheight
  • Baseheight height above ground level to show
    the feature.
  • Extrusion height to extend into air.
  • Both set under a layers properties.

34
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35
Using TINs Fly-throughs
  • With Arc 3D Analyst you can use such overlays to
    generate 3D scenes and fly-throughs.

http//www.ordnancesurvey.co.uk/oswebsite/gisfiles
/section2/movies/bennevis.mpa
36
Animation
  • Show the Animation toolbar.
  • Either push the Record button on the Play
    toolbar,
  • Or take keyframes and use the Animation Manager
    to string them together.
  • Push play to see them.
  • Can export to AVI files.

37
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38
Using TINS VRML
  • One format you can convert TINs into is VRML.
  • Also export VRML from ArcScene.
  • Virtual Reality Modelling Language.
  • This is easier to generate and manipulate than
    fly-throughs.
  • Comes in a text file that looks like HTML.
  • Users can then walk through the landscape.

39
What Arc isnt good at.
  • 3D where there are
  • Multiple layers
  • Variation in layer thickness
  • Interpolation of layer thickness
  • Non-layer 3D data
  • E.g Geology, Bridges, Building interiors.
  • For these you need a proper 3D package.
  • http//developer.viewpoint.com/index1.html?devdev
    eloperzone/5-213.jsp

40
Stuff We Havent Looked At
  • Thats it for the main body of the program!
  • Havent looked in detail at
  • ArcPlot
  • ArcGRID
  • ArcTIN
  • ArcWorkstation Network Analysis (Sections,
    Routes).

41
Stuff We Havent Looked At.
  • Geoprocessing Servers.
  • It is possible to get ArcDesktop to add in tools
    that are on another machine. These appear like
    any other tool.
  • Your client machine sends the server machine
    data and gets back results.

42
Stuff We Havent Looked At.
  • Hyperlinking Maps
  • ArcDesktop allows you to add
  • Spatial Bookmarks
  • Hyperlinks
  • popup Map Tips
  • associated metadata documents, e.g. Word files
    (see Enclosures in ArcCatalog Help).

43
Stuff We Havent Looked At.
  • ArcMap Magnifier, Overview, StyleManager.

44
Summary
  • We can examine Raster data in a number of
    formats, but to do analysis on it we really need
    to import it as a GRID in arc.
  • GRIDs can store Raster 3D information.
  • TINs can store Vector 3D information.
  • We can display by height / Z Value in classes or
    continuously, but we can also display aspect and
    slope data with TINs.

45
Summary
  • 3D Analyses include
  • Volume calculations (Cut and Fill, Volume).
  • Viewshed calculations.
  • Contour and boundary calculations.
  • We can output our data as fly-throughs (with 3D
    Analyst) and VRML.

46
Next Lecture
  • AML and Programming ArcInfo with Andy Evans
  • Mondays practical
  • Network analysis
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