3 Mapping of Spatial Data - TU Braunschweig · 2012-11-06 · •Mapping (visualization) of spatial...

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3.1 Properties of Maps

3.2 Signatures, Text, Color

3.3 Geometric Generalization

3.4 Label and Symbol

Placement

3.5 Summary

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 206

3 Mapping of Spatial Data

http://homepage.univie.ac.at/.../Janschitz_Text.pdf

• Mapping (visualization) of spatial objects by

transforming them into representation objects

(map objects)

• Map

– Generalized model in a reduced scale for representing

selected spatial information

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 207

3 Mapping of Spatial Data

http://www.xerokampos.eu/

• Topographic map

– Geometrically and positionally accurate

representation of

landscape objects drawn

to scale (topography,

water network, land

use, transportation

routes)

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 208

3 Mapping of Spatial Data

http://www.gps-touren.net/

• Thematic map

– Emphasis is on subject-specific information (geological

map, vegetation

map, biotope

map)

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 209

3 Mapping of Spatial Data

http://www.lung.mv-regierung.de/

• Challenges

– Projection of the 3D surface on two dimensions

(paper, film, screen)

– Selection of the spatial objects and their attributes to be displayed

– Generalization of geometric and thematic properties (simplify, omit depending on scale)

– Exaggeration and displacement (e.g. river valley with roads and railway lines)

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 210

3 Mapping of Spatial Data

http://maps.google.de/

• Graticule

– Mapping the earth (sphere,

ellipsoid) to a plane

– Two tasks

• Conversion of geographic

coordinates (longitude

and latitude) to cartesian

coordinates (x, y; easting,

northing)

• Scaling of the map

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 211

3.1 Properties of Maps

www.klett.de

• Projections on

– Cone

– Plane

(azimuthal

projection)

– Cylinder

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 212

3.1 Properties of Maps

[HGM02]

• Desired properties

– Length preservation: with plane maps only limitedly

attainable (in certain directions or at certain points)

– Equivalent (equal area): preserve area measurements

shape, angle, and scale may be strongly distorted

– Conformal: important

for navigation in

shipping and air

transport

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 213

3.1 Properties of Maps

http://www.quadibloc.com/maps/

• Areas and angles can not be preserved at the

same time, therefore

– Compromise projections minimize overall distortion

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 214

3.1 Properties of Maps

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• Example:

Conical

Projection

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 215

3.1 Properties of Maps

http://www.csiss.org/map-projections/

• Example:

Azimuthal

Projection

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 216

3.1 Properties of Maps

http://www.csiss.org/map-projections/

• Example:

Cylindrical

Projection

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 217

3.1 Properties of Maps

http://www.csiss.org/map-projections/

• The Gauss-Krüger coordinate system

– Used in Germany and Austria

– Cartesian coordinate system to represent small areas

– Divides the surface of the earth into zones

• Each 3° of longitude in width

• The zones are projected onto a cylinder with the earths

diameter

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 218

3.1 Properties of Maps

www.geogr.uni-jena.de/.../GEO142_3b.ppt http://homepage.univie.ac.at/.../Janschitz_Text.pdf

– Origin of the coordinate system:

intersection point of the central meridian and the

equator

– X coordinate from the

origin positive towards east,

y coordinate from the origin

positive towards north

– X and y values given in meters

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 219

3.1 Properties of Maps

http://www.gerhard-tropp.de/Troppo/gauss_krueger.html

www.geogr.uni-jena.de/.../GEO142_3b.ppt

– To avoid negative x coordinates the central meridian

is set to 500,000 m (false easting)

– Each projection zone (3°, 9°, ..., 177°) is identified

by a number (1, 3, …, 59)

– This number is placed prior to the x value

– Example: the Gauss-Krüger coordinates

x: 3,567,780.339 and y: 5,929,989.731

refer to the following location

x: 67,780.339 m East of the 9° meridian

y: 5,929,989.731 m North of the equator

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 220

3.1 Properties of Maps

• Structure of maps

– Body of the map presentation of the actual map

– Map margin contains name, map, scale, legend

– Map frame borders map, contains numbering of the respective coordinate system

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 221

3.1 Properties of Maps

http://www.apat.gov.it/

• Graphical design elements of maps are

– Symbols

(signatures)

for

• Points

• Lines

• Areas

– Text

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 222

3.2 Signatures, Text, Color

http://lehrer.schule.at/Ecole/

• The use of point, line, area symbols depends on

– Spatial scale of a map

– Purpose of the map

– Convention

• Point signatures are (composite) symbols for the representation of spatial objects with point geometry

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 223

3.2 Signatures, Text, Color

[HGM02]

• Line signatures represent objects with line geometry

• Area signatures represent objects with area geometry

• Texts are needed in various fonts for the labeling of maps

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 224

3.2 Signatures, Text, Color

[HGM02]

• Color

– Important design element

– Additive mixture

• Most relevant for displaying maps

on screen

• Common color space: RGB

– Subtractive mixture

• Most relevant for printing maps

• Common color space: CMYK

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 225

3.2 Signatures, Text, Color

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– There exist various

color tables

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 226

3.2 Signatures, Text, Color

http://i.msdn.microsoft.com/ http://us-shop-paderborn.com/

• For maps and map series the signatures on-hand,

fonts, and colors are specified in signature

catalogs and color

tables

– Example:

topographical map

1:25.000 (TK25)

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 227

3.2 Signatures, Text, Color

http://www.lgn.niedersachsen.de/

• Signature catalog "SK25" describes how the TK25 is derived

from the "digital landscape model" (digitales

Landschaftsmodell 1:25.000, DLM25)

• The catalog consists of derivation rules and signatures

(about

300

forms)

• Some

derivation

rules:

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 228

3.2 Signatures, Text, Color

• Some signatures:

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 229

3.2 Signatures, Text, Color

– Example:

• Real estate map 1:1000

• The ALKIS project (official property cadastre information

system, Amtliches Liegenschaftskataster Informationssystem)

specifies a signature library and derivation rules

• Approximately 670 signatures

• Approximately 850 derivation rules

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 230

3.2 Signatures, Text, Color

• A signature

specification:

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 231

3.2 Signatures, Text, Color

Section of a real estate map

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 232

3.2 Signatures, Text, Color

• The direct geometric derivation (coordinate

transformation) of map objects from spatial

objects works only with large-scale maps

(e.g. real estate

map)

• For small-scale

maps there are

too many details

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 233

3.3 Geometric Generalization

http://www.geobasis-bb.de/GeoPortal1/

• Generalization simplifies map content for the

preservation of readability and comprehensibility

• Replacement of scale preserving mappings

through simplified mappings, symbols, and

signatures

• Select and summarize information

• Maintain important objects, leave

out unimportant ones

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 234

3.3 Geometric Generalization

http://www.kartographie.info/

• Eight elementary operations

– To simplify

– To enlarge

– To displace

– To merge

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 235

3.3 Geometric Generalization

– To select

– To symbolize

– To typify

– To classify

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 236

3.3 Geometric Generalization

www.ikg.uni-hannover.de

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 237

3.3 Geometric Generalization

Base map 1:5000 Topographical map 1:25.000

[HGM02] [HGM02]

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 238

3.3 Geometric Generalization

Topographical map 1:25.000 Topographical map 1:50.000

[HGM02] [HGM02]

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 239

3.3 Geometric Generalization

Topographical map 1:50.000 Topographical map 1:100.000

[HGM02] [HGM02]

• Typical operations for generalization

(alternative view)

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 240

3.3 Geometric Generalization

[SX08]

• Smoothing of polylines by means of a simple

low-pass filter:

y(n) = 1/3(x(n)+x(n−1)+x(n−2))

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 241

3.3 Geometric Generalization

• Electronic filter that passes low-frequency signals

but attenuates high-frequency signals

• Further common filter types

– High-pass

– Band-pass

– Band elimination

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 242

3.3 Low-pass Filter

• Passive electronic realization

– Simple circuit consists of a resistor and a capacitor

(RC filter, first order filter)

– More advanced circuit with

additional inductor

(RLC filter,

second order

filter)

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 243

3.3 Low-pass Filter

http://upload.wikimedia.org/

http://ecee.colorado.edu/~mathys/

• Active electronic realization

– For example RC filter with an operational amplifier

– An operational amplifier has a high input impedance

and a low output

impedance

– Voltage gain is

determined by

resistors R1, R2

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 244

3.3 Low-pass Filter

http://www.electronics-tutorials.ws/

• Digital filters are realized as

– Finite impulse response

filter (FIR)

• Impulse response lasts for

n+1 samples and settles to zero

• Output is a weighted sum of

the current and a finite

number of previous values

of the input

– Infinite impulse response

filter (IIR)

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 245

3.3 Low-pass Filter

http://upload.wikimedia.org/

• A moving average filter is a very simple FIR filter

– All n filter coefficients

are set to 1/n

– Realization by means of

• Delay units

• Ring buffer

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 246

3.3 Low-pass Filter

http://upload.wikimedia.org/

http://blog.avangardo.com/wp-content/

• In offline mode (no real-time constraints)

a moving average filter results in a simple loop

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 247

3.3 Low-pass Filter

x[1...n] input values y[1...n] output values for (int i=2; i<n; i++) { y[i] = 0.333*(x[i-1]+x[i]+x[i+1]); }; y[1] = x[1]; y[n] = x[n];

• Adaptation of simple low-pass filter to

two-dimensional

geometry

x′i = ⅓(xi−1 +xi+ xi+1)

y′i = ⅓(yi−1 +yi + yi+1)

+ very efficiently to compute

− coordinates are changed, no reduction of points

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 248

3.3 Geometric Generalization

• Simplification of polylines

– Reduction of points

– No change of coordinates

• Douglas/Peucker algorithm [DP73]

– Given: polyline L, threshold g

– g is very small: L remains unchanged

g is very large: L is changed to

one single line

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 249

3.3 Geometric Generalization

• Douglas/Peucker algorithm

1. given: polyline L, threshold g

2. determine line between the start and end point of L,

3. determine the point of L that is furthest from the line segment

4. if distance > g then the point is significant, repeat procedure for both sub-lines, otherwise remove all the points between the start and end point of L

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 250

3.3 Geometric Generalization

http://en.wiki.mcneel.com/

Examples:

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 251

3.3 Geometric Generalization

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 252

3.3 Geometric Generalization

Properties:

+ simple base operation: distance measurement

− runtime of naive implementation: O(n2)

+ runtime of optimized implementation: O(n log n)

+ good results even with a strong reduction of points

+ extendable for polygons

− "outliers" are not eliminated

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 253

3.3 Geometric Generalization

• Polygon to polyline conversion

– Presentation of rivers and roads

– Text placement within polygons

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 254

3.3 Geometric Generalization

http://www.almenrausch.at/bergtouren/ http://www.naturathlon2006.de/

• Schoppmeyer/Heisser procedure [SH95]

1. Given: elongate polygon P

2. Determine the longitudinal axis of P

3. Drop the perpendicular from all edge points to the

longitudinal axis

4. Determine the intersection points of the extended

perpendicular lines

5. Determine the centre of the resulting axes

6. Connect adjacent centers

7. Determine suitable start and end segment

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 255

3.3 Geometric Generalization

Example

1. Given: elongate polygon P

2. Determine the longitudinal axis of P

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 256

3.3 Geometric Generalization

3. Drop the perpendicular from all edge points to the

longitudinal axis

4. Determine the intersection points of the extended

perpendicular lines

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 257

3.3 Geometric Generalization

5. Determine the centre of the resulting axes

6. Connect adjacent centers

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 258

3.3 Geometric Generalization

7. Determine suitable start and end segment

Result

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 259

3.3 Geometric Generalization

Using the result for text placement

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 260

3.3 Geometric Generalization

Properties:

+ relatively short runtime

+ quite good results with "good-natured" polygons

− determining the start and end segment

− procedure fails for non-elongate polygons

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 261

3.3 Geometric Generalization

• Procedure for arbitrary polygons Petzold/Plümer [PP97]

1. given: Polygon P (set of points S)

2. determine Voronoi diagram of S

3. determine intersection points of the Voronoi edges and the polygon edges

4. consider resulting Voronoi skeleton:

5. choose an appropriate sequence of edges

Voronoi diagram:

assigns each point Pi ∈ S the points of the plane that are closer to Pi , than to each Pj ∈ S, i≠j.

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 262

3.3 Geometric Generalization

Example

1. given: Polygon P (set of points S)

2. determine Voronoi diagram of S

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 263

3.3 Geometric Generalization

3. determine intersection points of the Voronoi edges

and the polygon edges

4. consider resulting Voronoi skeleton:

5. choose an appropriate sequence of edges

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 264

3.3 Geometric Generalization

Properties:

− selection of an appropriate polyline from the

skeleton

− computation of the Voronoi diagram

+ results for all kinds

of polygons

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 265

3.3 Geometric Generalization

Example (polygon with 2000 points):

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 266

3.3 Geometric Generalization

visualization tool: [Me11]

• Procedure with rasterization, thinning, and re-vectorization

1. given: polygon P (set of points S)

2. rasterization of P

3. topological thinning of P (building a skeleton)

4. line following and re-vectorization

5. determine the longest path

6. line simplification

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 267

3.3 Geometric Generalization

Example

1. given: polygon P (set of points S)

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 268

3.3 Geometric Generalization

2. rasterization of P

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 269

3.3 Geometric Generalization

visualization tool: [Bu11]

3. topological thinning of P

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 270

3.3 Geometric Generalization

visualization tool: [Bu11]

4. line following and re-vectorization

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 271

3.3 Geometric Generalization

visualization tool: [Bu11]

5. determine the longest path

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 272

3.3 Geometric Generalization

visualization tool: [Bu11]

6. line simplification

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 273

3.3 Geometric Generalization

visualization tool: [Bu11]

• Simplification of polygons

– Low-pass filter

– Douglas/Peucker (adapted)

Decompose polygon P into 2 polylines L1, L2 e.g. at the points

PL1, PL2 ∈ P, with maximum distance between each other

Simplify L1 and L2

Recombine resulting polylines at PL1 and PL2

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 274

3.3 Geometric Generalization

Example

polygon with points PL1, PL2 with maximum distance

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 275

3.3 Geometric Generalization

– Example

Douglas/Peucker (adapted)

city area of Braunschweig,

reduction from about 90 to about 30 points

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 276

3.3 Geometric Generalization

Further example

Douglas/Peucker (adapted)

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 277

3.3 Geometric Generalization

g = 0.5 g = 1

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 278

3.3 Geometric Generalization

cartographically desired generalization

results with Douglas/Peucker (adapted)

– Douglas/Peucker reduces the number of polygon points

– Characteristic shapes are preserved (within certain limits)

– Good results with "natural" geometries (bogs, lakes, forests)

– Less satisfactory results with polygons with predominantly right angles (buildings), therefore

• Modification to preserve right angles and long edges

• E.g. Neumann/Selke [NeS01]

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 279

3.3 Geometric Generalization

• Geometric generalization (and displacement) of

building sketches is a challenging task

• Convenient results achieved by programs

• E.g. CHANGE, PUSH, TYPIFY [Se07]

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 280

3.3 Geometric Generalization

http://www.ikg.uni-hannover.de/

• Placement of all texts (labels) in the same way

results with high probability in overlappings (poor

readability)

• Therefore, it is necessary

to move, scale down,

rotate, or omit texts

• In the general case this is

a NP-hard optimization

problem

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 281

3.4 Label and Symbol Placement

http://www.laum.uni-hannover.de/ilr/lehre/Isv/

• Objectives of labeling

– Easily readable

– Unambiguity: each label must be easily identified with exactly one graphical feature

– Same facts are represented in the same way

– Different facts are represented differently

– Important facts are emphasized

– Important objects are never covered

– No uniform pattern (avoidance of raster effect)

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 282

3.4 Label and Symbol Placement

http://www.mdc.tu-dresden.de/

• Text or label placement is divided into

– Point labeling • Positions to the right are preferred to those

on the left

• Labels above a point are preferred to those below

• E.g. cities with a horizontal label

– Line labeling

• Labels should be placed as straight as possible

• E.g. rivers with names

– Area labeling

• It must be clear what the total area is

• E.g. forest areas containing their names

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 283

3.4 Label and Symbol Placement

http://www.sprachkurs-sprachschule.com/

http://upload.wikimedia.org/

• For the three classes there are many specialized

algorithms, based on

– Greedy algorithm

• Labels are placed in sequence

• Each position is chosen

according to minimal

overlapping

• Acceptable results only for

very simple problems

• Very fast

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 284

3.4 Label and Symbol Placement

http://alitarhini.files.wordpress.com/

• Example

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 285

3.4 Label and Symbol Placement

– Local optimization

• The labels are checked several times

• On each pass a single label is repositioned an tested

• The position is kept, if the overall result improves

• Stop, if a local optimum is reached

• Suitable only for maps which relatively few labels

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 286

3.4 Label and Symbol Placement

– Simulated annealing

• Similar to local optimization, however yielding better results

• A placement of a label can be kept even though it (initially)

downgrades the overall result

• At first "high temperature", thus leaving local optima is

possible

• Later on ("low temperature") only

small changes are possible

• Challenges: a good evaluation function,

and a good annealing schedule

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 287

3.4 Label and Symbol Placement

http://www.hs-augsburg.de/informatik/

• Name and inspiration from annealing in metallurgy: controlled cooling of a material until it changes from liquid to solid

• Structure of the solid depends on „the cooling schedule“

– Fast cooling results in • Unordered solid

• Internal stresses

– Slow cooling results in • Ordered solid

• Low internal energy

• Macroscopic crystal lattice

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 288

3.4 Simulated Annealing

http://webuser.hs-furtwangen.de/~neutron/

• Example: SiO2

– Short range order: tetrahedron

– Crystalline form: Cristobalit

– Without long range order: Silica glass

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 289

3.4 Simulated Annealing

http://de.wikipedia.org/wiki/Glas

http://webuser.hs-furtwangen.de/~neutron/

Si O

• Elements

– Initial solution (liquid)

– Modifications (vibrations of molecules)

– Cooling schedule: Change of temperature over time

• Initial temperature

• Freezing point

– Weighting function (internal energy)

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 290

3.4 Simulated Annealing

• Pseudocode:

– Usually the temperature is decreased after multiple changes

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 291

3.4 Simulated Annealing

T = initialTemperature; currentSolution = InitialSolution; while (T > freezingPoint){ newSolution = CHANGE(currentSolution); if (ACCEPT){ currentSolution = newSolution; } ANNEAL(T); }

– Decision if the new solution is accepted

• A better solution is always accepted

• Probability of accepting a worse solution depends on the

temperature and its cost

• Boltzmann factor: e-E/k*T ; k = 1,3806504(24) · 10−23

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 292

3.4 Simulated Annealing

ACCEPT{ Δ = EVALUATE(newSolution) – EVALUATE(currentSolution) if((Δ < 0) or RANDOM(0,1) < e-Δ/T)){ return true; } return false; }

• Example: label placement

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 293

3.4 Simulated Annealing

http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.50.2327

• Initial solution: random label placement

• Weighting function

– Number of covered (or deleted) labels

– Consideration of cartographic preferences by

weighting of possible positions for point labels

• Modifications

– Move an arbitrary or covered label to a new position

– If cartographic preferences are considered an

arbitrary label should be moved

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 294

3.4 Simulated Annealing

2

4

1 5

6

8

7 3

• Cooling schedule:

– Initial temperature ca 2,47 → the probability of accepting that a solution whose cost are 1 higher is accepted is 2/3, i.e.: e-1/T = 2/3

– T = 0,1 * T

– T is decreased as soon as more than 5*n new solutions have been accepted (n is the number of objects)

– Search ends

• As soon as T has been decreased 50 times

• If none of 20*n new solutions in a row has been accepted

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 295

3.4 Simulated Annealing

• Result

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 296

3.4 Simulated Annealing

http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.50.2327

• Symbol placement (point signatures) is just as

complex as text placement

• In the following two examples for special cases

– Displacement and placement of trees symbols in

TK25-like presentation graphics [NPW06]

– Placement of point signatures in polygons of buildings

for real estate maps [NKP08]

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 297

3.4 Label and Symbol Placement

• Displacement and placement of tree row symbols

– Roads as well as tree rows are given as polylines only in the digital landscape model 1:25.000 (DLM25)

– Placement of the tree symbols on the points of the tree rows does not result in an equidistant pattern

– The visualization of roads is much wider than the actual street width (depending on the type of the road (attribute: dedication, “Widmung”))

– The tree symbols are often hidden by the line signatures of the streets

– Thus, beside a coordinate transformation an alternative placement and a displacement is needed

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 298

3.4 Label and Symbol Placement

• One single road from the DLM25

(example, XML/GML encoding)

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 299

3.4 Label and Symbol Placement

<AtkisMember> <Strasse> <gml:name> Badstrasse </gml:name> <AtkisOID> 86118065 </AtkisOID> <gml:centerLineOf> <gml:coord><gml:X>4437952.980</gml:X><gml:Y>5331812.550</gml:Y></gml:coord> <gml:coord><gml:X>4437960.070</gml:X><gml:Y>5331818.450</gml:Y></gml:coord> <gml:coord><gml:X>4437967.200</gml:X><gml:Y>5331825.410</gml:Y> </gml:coord> </gml:centerLineOf> <Attribute> <Zustand> in Betrieb </Zustand> <AnzahlDerFahrstreifen Bedeutung=“tatsaechliche Anzahl”> 2 </AnzahlDerFahrstreifen> <Funktion> Strassenverkehr </Funktion> <VerkehrsbedeutungInneroertlich> Anliegerverkehr </VerkehrsbedeutungInneroertlich> <Widmung> Gemeindestrasse </Widmung> </Attribute> </Strasse> </AtkisMember>

• A tree row from the DLM25

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 300

3.4 Label and Symbol Placement

<AtkisMember> <Baumreihe> <gml:centerLineOf> <gml:coord><gml:X>3524258.170</gml:X><gml:Y>5800238.690</gml:Y> </gml:coord> <gml:coord><gml:X>3524256.190</gml:X><gml:Y>5800220.270</gml:Y> </gml:coord> <gml:coord><gml:X>3524255.240</gml:X><gml:Y>5800196.070</gml:Y> </gml:coord> ... <gml:coord><gml:X>3524581.650</gml:X><gml:Y>5799674.000</gml:Y> </gml:coord> </gml:centerLineOf> <Attribute> <Vegetationsmerkmal> Laubholz </Vegetationsmerkmal> </Attribute> </Baumreihe> </AtkisMember>

• Direct visualization

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 301

3.4 Label and Symbol Placement

• Simple displacement procedure

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 302

3.4 Label and Symbol Placement

for all t : treeRow do begin if exists s : street (distance(t,s) ≤ minDistance(s.dedication)) then for all p : t.coord do begin r := refSegment(s,p); move(p,r) end do end if end do;

• Visualization with displacement

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 303

3.4 Label and Symbol Placement

• Placement procedure

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 304

3.4 Label and Symbol Placement

for all t : treeRow do begin l := length(t.centerLineOf); n := ⌊l/distanceConst⌋ + 1; t’ : new treeRow; for i=1 to n do begin computePoint (t’.coord[i], t.centerLineOf, distanceConst) end do end do;

• Visualization with displacement and placement

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 305

3.4 Label and Symbol Placement

• Placement of point signatures in polygons of buildings

– Derivation of the real estate map (1:1.000) from ALKIS

inventory data extracts relatively straight forward

– No generalization and no displacement is needed

(topographic planimetry, "cadastral map")

– Representation of buildings, parcels, border points, etc.,

with the given signature library and the derivation rules

– E.g. symbolisation of buildings as colored polygons with a

boundary line and a typical point signature depending on

the attributes building function (Gebäudefunktion) and

further building function (weitere Gebäudefunktion)

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3.4 Label and Symbol Placement

• A building from an ALKIS inventory data extract

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3.4 Label and Symbol Placement

<gml:featureMember> <AX_Gebaeude gml:id="DEHHSERV00001FN1"> ... <position><gml:Polygon> <gml:exterior><gml:Ring> ... <gml:pos>3567807.047 5930017.550</gml:pos> <gml:pos>3567810.850 5930024.755</gml:pos> ... <gml:pos>3567807.047 5930017.550</gml:pos> ... </gml:Ring></gml:exterior> </gml:Polygon></position> <gebaeudefunktion>2000</gebaeudefunktion> <weitereGebaeudefunktion>1170</weitereGebaeudefunktion> <bauweise>2100</bauweise> <anzahlDerOberirdischenGeschosse>1 </anzahlDerOberirdischenGeschosse> </AX_Gebaeude> </gml:featureMember>

• For many point signatures which are related to buildings so-called presentation objects are supplied in the inventory data, defining the optimal position of the respective signature (given in "world coordinates")

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 308

3.4 Label and Symbol Placement

<gml:featureMember> <AP_PPO gml:id="DEBWL00100000fAW"> <lebenszeitintervall>... </lebenszeitintervall> <modellart>... </modellart> <anlass>000000</anlass> <position> <gml:Point><gml:pos>3540847.175 5805897.864</gml:pos></gml:Point> </position> <signaturnummer>3316</signaturnummer> <dientZurDarstellungVon xlink:href="urn:adv:oid:DEBWL00100000jwR"/> <drehwinkel>67.000</drehwinkel> </AP_PPO> </gml:featureMember>

• But some buildings lack the presentation objects

• An obvious, easily determined position for the

signature:

– Choose the center of the smallest axis parallel

rectangle, which encloses the polygon of the building

– min(x1, ..., xn)+((max(x1, ..., xn)−min(x1, ..., xn))/2),

– min(y1, ..., yn)+((max(y1, ..., yn)−min(y1, ..., yn))/2)

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 309

3.4 Label and Symbol Placement

• Unfortunately, the results are not always satisfactory

• Therefore, heuristic procedure, based on

– Convexity

– (approximate) symmetry points

– (approximate) symmetry axis

– Various quality criteria

– Discrete increments

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 310

3.4 Label and Symbol Placement

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 311

3.4 Label and Symbol Placement

if polygon of building convex: choose centroid if signature frame fits completely in polygon of building: place there otherwise choose appropriate point with the smallest distance to the centroid else if symmetry point in polygon of building: place there otherwise further procedure with symmetry axes

⇒ generation of a new presentation object with "optimal" positioning coordinates

• The procedure is not suited for the placement of

signatures for churches/chapels

– Besides the determination of an appropriate position

– Also the signatures alignment to the shape of the

building’s polygon is needed

– An alignment to the north south axis is rarely optimal

– Crosses for churches as parallel as possible to the

churches naves

– Crossbrace of cross should be

placed in the transept

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 312

3.4 Label and Symbol Placement

• Heuristic procedure

– Determine a preferable large cross that just fits in the

building’s polygon

– Proportions of the large cross and the church

signature are the same

– If the large cross is found, place the signature just in

the intersection point

• For this purpose first simplify the building’s

polygon

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 313

3.4 Label and Symbol Placement

• In several rotation angles: look for a preferable large, well placed cross

– Restriction of the potential rotation angles and positioning points (e.g. consider minimum distance to boundaries of the building’s polygon)

– Evaluate all appropriate crosses within a rotation angle

– Evaluate all the best crosses (e.g. lengths of the crosses, alignments)

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 314

3.4 Label and Symbol Placement

• Placement of the signature in the best cross of all

rotation angles

⇒ Generation of a new presentation object with

"optimal" positioning coordinates and

"optimal" rotation angle

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 315

3.4 Label and Symbol Placement

• Both methods applied to inventory data extracts

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 316

3.4 Label and Symbol Placement

• Mapping of spatial data

– Topographic map

– Thematic map

• Properties of maps

– Graticule

– Projections

– Gauß-Krüger coordinate system

– Body of map, map frame, map margin

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 317

3.5 Summary

• Signatures, text, color

– Point signatures

– Line signatures

– Area signatures

– Derivation rules

– TK25, real estate map

• Geometric generalization

– Smoothing of polylines

– Simplification of polylines

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 318

3.5 Summary

– Douglas/Peucker algorithm

– Polygon to polyline conversion

– Simplification of polygons

– Geometric generalization of building’s ground plans

• Text and symbol placement

– Methods for text placement

simulated annealing

– Displacement and placement of symbols for tree rows

– Placement of point signatures in building’s polygons

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 319

3.5 Summary

2

4

1 5

6

8

7 3

Spatial Databases and GIS – Karl Neumann, Sarah Tauscher– Ifis – TU Braunschweig 320

3.5 Summary

GIS graticule

map

text signatures

color

collect

manage

analyse

display

generalization

area labelling

simplifying lines

polygon→ line

design elements

placement

topographic

thematic

building signatures

tree rows as optimization problem

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