Interactive generalization on large-scale topographical map supported

Geo-spatial Information

Volume 6 ,Issue 4 ,Page 17-26

Science (Quarterly)

December 2003

Interactive Generalization on Large-Scale Topographical Map Supported by a Database Platform CAI Zhongliang

WU Hehai

1

DU Qingyun

LIAO Chujiang

Introduction The

traditional

needs the

manual

operators

to

cartographic master

generalization

enough

professional

knowledge and skills and to possess certain work experilarge scale topographic

ence, which is very difficult to be fulfilled. Furthermore,

map~ interactive generalization; data

this method brings about low efficiency, a long time con-

K E Y WORDS

platform

suming as well as big contrived errors. With the transfor-

ABSTRACT

This

paper makes

a

study on the interactive digital generalization,

where

map

generalization

mation of u s e r ' s consumption concept, as far as map production is concerned, a swift reaction to market is

can be divided into intellective reason-

demanded. Obviously, for its poor efficiency, this kind of

ing procedure and operational proce-

map production whose majority is constituted by paper

dure, which are done by human and

map is difficult to meet the users' demands. In a d d i t i o n ,

computer, respectively. And an inter-

it can not keep up with the quick development of informa-

active map generalization environment

tion at all.

for large scale topographic map is then designed and realized.

This research

focuses on: (D the significance of researching an interactive map generalization environment, ~) the features of large scale topographic map and inter-

At present, to a great extent, the manual method still prevails in map generalization. That is to say, on one hand, we have achieved automatic c a r t o g r a p h y , on the other hand, we are adopting manual cartographic generalization. It will be too difficult for the performers to sim-

active map generalization, (~) the con-

ultaneously work under two different environments, which

struction of map generalization-orien-

will also destroy the system of automation and integra-

ted database platform.

tion. In order to meet new requirements presented by digital environment, it should be a development direction of map making to adopt new technology to improve the efficiency of map compilation.

CAI Zhongliang, Ph. D candidate, School of Resource and Environment Science, Wuhan University, 129 Luoyu Road, Wuhan 430079, China. E-maih zhongliangcai@ yahoo, corn. cn

18

Geo-spatia/ Information Science (Quarterly)

on the generalization of geometric information

Large-scale topographic map and interactive cartographic generalization

2

and the disposal of topological relations between elements. Urban large-scale topographic map is characterized by numerous man-made map elements (such as house, street, pipe net, construction facility, etc).

2.1

Differing from natural fea-

Characteristics o f large-scale topographic

tures, these features take on obvious human

map

traits. For instance, the borders of streets can not embody fractal characteristics as natural

By means of graphics decomposition, largescale topographic map may consist of the fol-

features (rivers, c o a s t l i n e s , ' e t c ) do.

Qn the

whole, the features distributing with human traits

lowing two parts: map graphics and character

develop a unique structure. For example, the an-

annotation. The former includes three kinds of

gel of a house polygon is a right angel, and the

graphics elements, point, line and area.

houses lying beside the two sides of roads are

A

digital topographic map must cover all spatial

regular and in arrays.

information and attribute information of six types of features: single feature, residential

2.2

scale topographic map

area, drainage basin, relief, pipe line and border, vegetation.

Interactive generalization based on large-

In terms of large-scale

Looking through the characteristics of large-

topographic map, because almost all human

scale topographic map mentioned above, we

and natural trivial elements on the earth sur-

can conclude that its represention of content

face require to be precisely and really reflec-

elements is more detailed, and the relations

ted and added to the considerable amount of

between them are also more complex.

information. Due to the quick changing and

ently, the basic theory of automatic generali-

updating speed, the verisimilitude these ele-

zation

is not mature.

ments is very bad, which embodies more obvi-

purely

automatic

ously when man-made elements are represen-

such complex information relations is hardly

ted.

possible at all.

In large-scale maps, the entities represented by

characteristic

Therefore,

generalization

Pres-

realizing based

on

By taking insight into the of

large-scale

topographic

features are difficult to form objects, the majority

map, it is not difficult to find out the majority

of them consist of complex geometric structures,

of characteristics and relations of map con-

and this kind of extraordinarily elaborate ex-

tent elements,

press, to certain extent, affects the simplification

Interactive generalization, however, is a hu-

and abstraction of data model based on the ob-

man-computer cooperative working style. Dur-

jective world. When added into the database,

ing the course of generalization, the performer

this kind of data representation is little similar to

is required to participate in such work as se-

a full replication; the scattered structure of the

lecting generalization operators, setting pa-

entity world still remains unchanged. For exam-

rameters, feeding back the executing resultS,

ple, in 1 : 1 000 scale map, a house is not only

etc.

denoted as a simple polygon, but attaches some

software arithmetic, executes the basic gen-

other linear structures, such as balcony, porch

eralization

and its pole, ladder, stairway etc. That is to

process as a whole may be summarized as the

say, the majority of objects are compound, which

problem of 3W-4- H. That is, When

aggravates the difficulty of cartographic seman-

does the user put forward the condition of

tics identification, and make operators designed

generalization and simplification to execute

for cartographic generalization excessively focus

the generalization transformation of shorten-

And computer, operation.

depending on certain The

generalization when

CAI Zhongliang,et al/Interactive Generalization

ing scale~ Where

on

Large-Scale-., 19

where do the spatial oc-

structure relations that the map generaliza-

cupancies generate conflicts, and where are

tion operations need, among which the hierar-

the features too dense~ Which

chical organization method is regarded most

tures are important~ How cartographic

how to execute

simplification,

and conflation etc.

which feareplacement,

In these problems,

3W

important. (1) The hierarchies of the generalization objects should be partitioned logically.

problems belong to the deeds involving in

traditional

powerful intellective generalization,

reason-

execute it on different hierarchies. This idea

ing, and judgment, which can presently only

is still of significance in software designing. It

be solved by hand. But H problems can be ac-

is essential to construct versatile map layer

complished by perfect generalization opera-

manager, which is used to provide the compil-

tors. indeed, in the whole task, the disposals

ation functions orienting operations. After the

of 3W problems account for a larger propor-

hierarchies of objects to be generalized are

tion, however,

as is

partitioned, the generalization operators to-

known to us, can swiftly arrive at an answer,

ward these hierarchies and the corresponding

which consumes a little time.

H problems,

control parameters will be determined eventu-

dealing with the compilation and maintenance

ally, which are the foundation of application

of geometric graphs, should be categorized

module development in the subsequent gener-

into physical labor. Provided they are solved

alization process.

our brains'

thinking,

cartographic

In the

generalization,

we

by hand, it might need a very long time. So

During the course of partitioning the hierar-

adopting this generalization method, human

chies, such respects as the basis of classifi-

and computer achieve a kind of mutual com-

cations of map cor~tent elements, geometric

plement through cooperative work. Compared

features (including

to the traditional manual operation, its effi-

e t c . ) , spatial relativity etc. should be given

ciency proves to be an evident improvement.

enough consideration.

point,

line,

area,

net,

Consequently, it can be seen that the design

The generalization element hierarchy should

and construction of data structure and data

approximately embody three characteristics.

model directly determine whether the charac-

operational sequence,

teristics and demands of interactive generali-

and element hierarchies' overlapability.

zation based on large-scale topographic map

erational sequence suggests that while sol-

can be rightly and flexibly reflected.

ving spatial conflicts among elements of dif-

structural

singularity Op-

ferent hierarchies, the priority of generaliza-

3

Construction of map generalization-oriented database platform

tion must be taken into account, keeping the features with the higher priority immobile, and deleting, cutting, replacing the features with less priority. The purpose of structural singu-

3. 1

Hierarchical organization o f generaliza-

larity is to meet the operational requirements

tion objects

of generalization operators.

Element hierar-

chies' overlapability is designed to realize all While designing the basic platform of map

the element

hierarchies'

overlapping

after

database (which includes designing the data-

they are generalized, so that we can adjust

base model and organizing the data struc-

spatial relations between them and eliminate

ture), the development of the subsequent ap-

the conflict contradictions.

plication functions should be sufficiently taken into

account,

and

the

designed

(2) in the software system, how to organize

platform

the hierarchy relations before generalization and

should present data objects with all kinds of

after generalization is also a problem that should

20

Geo-spatial Information Science

be solved.

(Quarterly)

Generalization operations, not the

behavior is not very compact.

Meanwhile, the

same as those common graphics editing opera-

CO method develops such outstanding peculiari-

tions, which may either directly substitute new

ties as modularity,

obiects for old objects,

the original

and hiding, abstraction inheritance, polymor-

state by using undoing operations, involve in

phism etc., which offers a most valid instrument

considerable complicated computations. Further-

and approach for managing large software and

more, under most situations, the operational ob-

advancing software reliability, reusability, ex-

ject is always towards multi-item. In the interac-

pansibility and maintainability.

or

resume

information encapsulation

tive undertakings, in fact, whether a generaliza-

When building large-scale topographic map

tion operation is in accordance with criterion is

database, generally, we pay little attention

mainly justified by performer. Because this kind

to the need of cartography, but focus on con-

of justice is achieved through comparing the state

sidering it as a geographical information da-

before the generalization with the one after the

tabase.

Thereby it is spatially vital to exe-

generalization, it is entirely wrong to adopt the

cute the abstraction of data type. This system

editing operations similar to replacement. The

database platform, based on the characteris-

generalization results ought to be derived from

tics of cartographic generalization and GIS,

the base map data. For adapting to this require-

CAD technology, can be abstracted as graph-

ment, it is necessary to simultaneously store two

ics, layer, object, geometrical class (inclu-

hierarchies of data before generalization and af-

ding point class, line class, area class, an-

ter generalization.

notation class, path class, region class, and

3.2

group class).

Design o f system based on object-oriented

The hierarchical structure can

be described as. g r a p h i c - > l a y e r - > o b j e c t - >

( 0 0 ) method

geometrical class, combining with the opera-

The O9 method takes objects as the most fun-

tion class related to the cartographic general-

damental elements, overcoming the disadvanta-

ization. The design of the system may be in-

ges that the relation between data structure and

terpreted in Fig. 1.

[ Generalization index ,

l

, Gridindex

I Data~ f

Graphicsclass

}

Geometric

,

query [

l

l

[[

Objectclass

I[ ~-[

I

Drainage

Lineclass Area class

_~

Generalization class

Relief Road Point class

Annotationclas Routeclass ----~I_ Regionclass - I Groupclass

query [

[ Datainput I t }

Building

Layer class

Conditioned

i i n me

I

t

Polygon

t i

[ [

Line Buffer

I I

I Triangulation network

I

{

I

Fig. 1 Designof the system

-.

operators class

] ] ],c

CAI Zhongliang,et al./Interactive Generalization on Large-Scale-.- 21

The object class of this system mainly con-

design and data interface, etc.

sists of four parts: system interface, map database management platform, tors and arithmetic,

The map database management platform class

basic opera-

includes graphics class, point class, line class,

element generalization

area class, annotation class, path class, region

process. Besides, it includes graphic symbol Table 1

class, and group class (Table 1).

Classes of map database platform

Object class

Descriptions of main attributes

Main operations

Graphics class

scale denominator, graphics name, scope, underling layers and geometric elements of spatial index,coordinate system,saved file name

create, data input, data output, index constructing, delete, read and write, show, save

Layer class

State, layer name, operation characteristics, geometric properties, underling geometric elements

create, copy, move, delete, show, data input, construction maintenance

Geometric object class

Geometric coordinates, attributes, state, keyword, boundary rectangles, index grids, structure relations

add, delete, move, read and write, show, register, grid index building, topology organizing

The element generalization process class in-

vegetation class, and relief class (Table 2).

cludes building class, drainage basin class, Table 2

Feature Generalization classes

Object class

Descriptions of main attributes

Main operations

Building class

Coordinates of building polygon, the layers of building, structure of building, adjoining buildings, shape, the smallest boundary rectangle

Partition of buildings groups, contiguous buildings recognition, replacement of building, simplification of shape, deletion, eonflation, evaluation

Drainage basic class

Coordinates of polygon, properties of triangulated network, minimum bounding rectangle, the description of shape, the relations of polygons

Recognition, filtration, deletion of small lake, bi-linc river is converted into single-line river, elimination, eonflation, simplification, and evaluation of islands

Road class

Coordinates, length, properties of road, the descriptions of part convex, contiguity relations, the characteristics of bends

Deletion, conflation, join, replacement, extraction of axis, simplification, summary of bends properties, elevation

Relief class

Coordinates. characteristics, elevation, contiguity relations of contour lines, valleys, ridges, elevation points

Filtration, join, deletion of contour lines, simplification of bends characteristics, constructing Voronoi, smooth-

Vegetable class

Coordinates, area, perimeter, attribute characteristics, contiguity relations, the characteristics of bends on boundary, and shape of polygon

The generalization operator class may be divided

into Delaunay

triangulation Table 3

hess

Deletion, simplification, combination, replacement, constructing Delaunay Triangular network, evaluation

class, overlay analysis class, etc (Table 3).

network Generalization operator classes

Object class

Descriptions of main attributes

Main operations

Triangulated irregular network class

Coordinates of group points, conditions of triangulated network, the vertexes of triangle, neighboring triangles, the center of triangular gravity

Contraction of Delaunay triangulated network, predisposal of data, extraction of axis, contraction Voronoi diagram, triangulate network maintenance

Overlay analysis class

]:kmndaries of polygons, the attribute conditions, islands, contiguity relations

Overlay analysis, computation of minim u m bounding rectangle, difference combination, simplification, uniting, conversion between vector and raster

While carrying out module design, this system

class, through multi-parent inheritance, can obtain

makes the best use of the inheritance and polymor-

the inheritances of all kinds of operations defined

phism. For example, the element generalization

by a set of generalization operators.

22

3.3

Geo-spatial Information Science (Quarterly)

organized in accordance

Logical organization o f generalization-o-

with the system:

g r a p h i c s - > ~ayer-:> eiement ciass-~> object-:>

riented map database

geometric attribute description, which may be

Logistic hierarchical structure of database is

expressed as in Fig. 2.

Graphics

I

Layer 1

r-H

I

I

Layer 2

I

Layer n

Layer 3

,

,

I

Point Line

,

i

Annotation

Area

I

I

I

I

Path

Region

Group

I Area objech

111

I

I

I

I

objecE ... objectm Geometric coordinates

Spatial grid index

Minimum bounding rectangle --

Code Attributes defined by user

Topological structure J

Fig. 2

Keyword

Logical constructionof database

The idea of from up to down adopting tree

used to describe and save such simple entity

structure to build database, ensures the con-

objects as single facility, road, communica-

sistence between the physical storage of pro-

tion line, building, vegetation, lake, illumi-

gram realization and the application-oriented

nation text, enterprise name, etc. but path,

logic structure, that is, as early as the time of

region, and group are used to express com-

storage and managing database, the hierar-

pound objects. Path is used for the storage of

chical relations is embodMed, so we can di-

drainage basin network and road network; re-

rectly acquire the informalion we retrieve with

gion is used for the storage of such group pol-

no excess search calculations needed, impro-

ygon structure as the buildings group and

ving the usage efficiency of the database.

lakes group, etc;

group is used to express

tn Fig. 2, all objects in this database are

those compound structures of objects, wnich

registered in a spatial grid index, which will

may be any type. However, here it should be

sequentially quicken the feedback speed of

emphasized that path, region and group only

the object identification and retrieval.

provide compound objects with the storage of

Similar to the hierarchical organization of data-

structure frame, because the compound objects

base, we may build the hierarchical structure of

mentioned above are all derived from simple ob-

object classes based on object-oriented design i-

jects by means of relational operators and addi-

dea. !n every class, the encaps-lat!cn are exerted

t!ve information. We need not save the s!mple

on the descriptions of class and the operations to

objects a second time. We only save the basic

data members, meanwhile, according to the affili-

structures of these compound objects in data-

ations of the data members and the object charac-

base, through which we can certainly get con-

teristics, we build a serial of inheritance relations

crete data. For example, in the buildings gener-

among graphics, layer, element class, object.

alization, according to the spatial contiguity re-

In the seven kinds of element class defined

lations, some simple polygon structures of build-

above, point, line, area, and annotation be-

ings are identified forming a group structure. At

long to the simple object types, which are

this time a compound object is derived from it,

OAI Zhongliang,et al./Interactive Generalization on Large-Scale..-

and we only need save it using region group

where ( X ,

structure.

(x,

y)

Y)

23

is the database coordinate;

is the virtual geodesic coordinate;

The design of path and region structure in

(x,,,~,, x . . . . y .... y .... ) is the range of virtual

this paper shares the idea of using network to

geodesic coordinate; R is the zoom coefficient of

analyze path and using region to analyze re-

the transformation from geodesic coordinate to

gion in Arc/Info system. The compounding re-

database coordinate; U is the unit of geodesic

lation between simple objects and compound

coordinate, such as meter; S is the system reso-

object is also approximately coincident with

lution; M is the denominator of scale.

the idea in Arc/Info system.

3. 4. 2

3.4

nate to d r a w i n g coordinate

Coordinate system

The transformation formula from the data-

Coordinate systems involved in this database include:

T r a n s f o r m a t i o n f r o m database coordi-

base coordinate to the drawing coordinate is:

geodesic coordinate system,

X=~-

drawing coordinate system before generalization, drawing coordinate system after generalization, database coordinate system, outwhere ( X ,

put device coordinate system, etc. The map database generalization is the operation on graphics using virtual geodesic coordinate, but it is necessary to decide the executions of operations through the u s e r ' s vision under drawing coordinate system. The index rules of generation are also described under the drawing coordinate system. For exam-

(x,

y)

Y) is the database coordinate;

is the drawing coordinate; S is the

system resolution. 3.4.3

T r a n s f o r m a t i o n f r o m base l a y e r coordinate to g e n e r a l i z a t i o n l a y e r coordinate

The transformation formula from the base layer coordinate to the generalization layer coordinate is.

M' l

X = ~,.,ac

ple, we rule the minimum interval among houses is l m m , twenty single facility objects per

"

Y = ~-Ty

sq. dm, etc. In A u t o M a p s o f t w a r e , the logical descriptions of d a t a ,

in the drawing coordi-

(4)

where ( X , Y ) is the generalization layer co-

nate system before generalization, are desig-

ordinate; ( x ,

nated to adopt mm as unit, and during the

nate; M2 is the denominator of scale after

course of physical storage of d a t a , the coor-

generalization; M , is the denominator of scale

dinates describing data are transformed into

before generalization.

database coordinates.

y)

is the base layer coordi-

The discrepancy be-

Because AutoMap software is mainly used to car-

tween the two kinds of coordinates is only a

ry out cartographic generalization based on large-

multiple which takes the resolution in the sys-

scale topographic map, it is not necessary to con-

tem as a coefficient, and the coordinate ori-

sider the projection transformation. While output-

gin lies in the center of drawing.

ting data, this system will question the selection

3. 4. 1

T r a n s f o r m a t i o n f r o m geodesic coordi-

from the geodesic system, drawing system before

nate to database coordinate

generalization, and drawing system after generali-

The transformation formula from the geodesic coordinate to the data coordinate is.

zation. The data type of this system database is integer type, owing to the characteristic of real 32 bit in Windows NT system. The expression of inte-

(1) y

=

TEy- (y~,,q- y,,,,,)~ R -- 1 O00U S M

ger type data is four bytes.

Meantime, in the

drawing coordinate system, we select O. 01 mm as (2)

resolution, both the two accuracies can meet the demand of the cartographic generalization.

24

3.5

Geo-spatial Information Science (Quarterly)

Spatial grid index

In order to improve the speed of querying the objects in this database, the spatial grid index technology is widely adopted in the spatial database development. The bottom query in relate to spatial localization includes two

registered with respect to the little square determined by the localization point and the size of every word~ and path, region,, group objects are not built a grid index.

3.6

Building and maintenance o f map database

aspects= one is to query which objects there

The data source building database is ap-

exist in a grid, and the other is to query which

proximately data files containing topological

grids a object lies in. The former is mainly ap-

structure and attribute information, and the

plied to objects identifying and retrieval by

operations building database are mainly com-

window, while the latter is mainly applied to

pleted by correlative functions defined in map

objects registering and grids index mainte-

class, here we only make several rough rules

nance after some objects are deleted. To re-

for the process of building database=

alize bi-directional query, a good method is building a bit matrix that takes the serial

O reading information content files of data source,

numbers of grids as the rows and takes the

(~) regrouping topological relation, getting

k e y w o r d s o f objects as the lines. However, in

the information about the arcs forming poly-

this software, due to the enormous amount of

gon and the external ring of islands,

objects (if twenty-five ] : I 000 map sheets

(~) performing the register of point, line, are-

are joined, the number of pints, lines and are-

a, and annotation objects,

as will add up to more than 80 000), the a-

them in the grid index,

mount of storage needed by the matrix is so large that the bi-directional query is difficult to achieve.

and registering

O saving the series of keywords, coordinate strings and header information of objects. After the data are read into AutoMap, the

This system selects the single-directional stor-

system does not immediately create external

age, that is, for the n n grids, we do not register

memory files, but saves all of them in memory

which grids a object goes through, but register

buffer to perform

management

operations.

the objects keywords contained in every grid,

Only when the storage operations are activa-

which meet the demands of the objects identif-

ted, are the external memory files= * . amg,

ying and retrieval. When the user delete a ob-

*.xy,

* . k e y created and saved.

ject, this system executes the real-time register

It is a complicated process to maintain the

calculations, then Iogouts the corresponding key-

database, after the user deletes an object,

words contained in the grids that this object goes

the corresponding operations include.

through, because the registration calculations

O removing the object keyword,

need not spend much time, and this kind of real-

Q removing the registers of this object in the

time calculation has no effects on the running efficiency of the system. When the system registers objects, the point

correlative grid indexes, Q maintaining the information of the relations between this object and other objects.

objects, according to the grid locations they lie

Taking arc as an example, after an arc is

in, are registered point objects keywords~ line

deleted, the polygon containing this arc will not

objects are registered line objects keywords in

exist, either. It must be emphasized that all ob-

terms of the girds serial numbers they go through~

jects' deletion operations don not include imme-

but for area objects, this system registers their

diately calling back their storage spaces. As the

keywords in the grids that their minimum boun-

user performs undoing operations, the system on-

ding rectangles cover, annotation objects are

ly needs to change 0 into 1.

OAI Zhongliang,et al./Interactive Generalization on Large-Scale-.- 25

3.7

culations of the results.

Design o f database query

In query class, such a group of bit operation

The query of this system is designed as the

functions are defined: READ bits, WRITE bits,

three manners: query according to spatial po-

MODIFY 1 or O, AND, OR, XOR c a l c u l a t i o n s ,

sitions ( l o c a l i z a t i o n

TRANSFORM bit strings into selected objects

identification,

windo-

wing, arbitrary p o l y g o n ) , query in terms of

keywords, etc.

logic conditions (element code, layer, geometric

character

class,

area,

perimeter,

4

Experiments and analysis

etc. ) and query with respect to structure relations. The query results of different processes can be carried out AND, 9

XOR compoun-

Taking the ] : 1 000 and I : 10 000 d a t a b a s e data of Shenzhen city as examples, the authors producted a number of experiments. The

ding for any times. The query result employs bit strings to express;

results proved that this kind of cartographic

an integer of integer type denotes 32 bit strings,

generalization

then 6 000 integers of integer type can denote 192

had high s t a b i l i t y ,

oriented

database

000 bit strings. The position of bit represents the

computer interactive generalization environ-

value of the keyword. That the value of bit is ]

ment based on this database can well help

denotes that the keyword has already been se-

performers finish the generalization work un-

lected; or it has not been selected, The method

der the digital environment (Fig. 4 and Fig. 5).

of bit express perfectly supports the logical c a l -

Though the automatic degree is not very high,

a[::]Uo