ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS", Bangkok, May 23-25, 2001
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NON-LINEAR RECTIFICATION OF MAP WITH COLLINEAR CONSTRAIN
Wei LU, Takeshi DOIHARA
Research Institute, Asia Air Survey Co., Ltd., 3F Asahi-Seimei Bldg.
8-6 Tamura-cho, Atsugi-shi, Kanagawa-ken, 243-0016, JAPAN
Tel:+81-462-95-1886, Fax:+81-462-95-1934
E-mail:luwei@aiiko.co.jp
Key Words: Digital mapping, Map rectification, GIS
Abstract
Map rectification has been playing a very important role in digital mapping processes. Especially in Japan, the ancient cadastral maps-
even though being only roughly correct in topology, area, and shape- are still being used as formal legal documents for clarification of
land rights. To digitize such kind of maps, rectification methods of non-linear transformation are required. In many cases, cadastral line
segments that are collinear to each other must also be kept collinear after transform. This constrain makes non-linear transformation
more difficult. In this paper, we propose a method that performs non-linear rectification while keeping the collinear relationship.
1. Introduction
Nowadays, with the rapid development of information technology
from algorithms to infrastructures, more and more GIS data are
being generated digitally. Even though digital data is the most
favorable form for GIS system, their tremendous cost does not
allow production from scratch when budget is not feasible. On the
other hand, there has been a huge collection of paper-based map
in all kinds of organizations. By digitizing these paper-based
maps and making proper edition/modification, we can generate
up-to-date map more economically. Since paper-based maps
usually have distortions due to the precision limitation of
production or data source, map rectification has been playing a
very important role in digital mapping processes. Especially in
Japan, the ancient cadastral maps- whereas being roughly
correct in topology, area, and shape- are still being used as
formal legal documents for clarification of land rights. To digitize
such kind of maps, rectification methods of non-linear
transformation are required. In many cases, cadastral line
segments that are collinear to each other must also be
maintained the same after transform. This constrain makes
non-linear transformation more difficult. In this paper, we propose
a method that performs non-linear rectification while keeping the
collinear relationship.
2. System Overview
Fig. 1 shows the overview of our system. The paper-based map is
first automatically converted to polyline and text. Due to
deterioration of paper or ink, there will be missing, corrupted, or
extra noisy data, which will be modified in the “Initial Manual
Modification” module. The next module generates the collinear
constrains in a semiautomatic way. The “Non-linear
transformation” module will then transform the digitized map
without breaking the collinear condition. Finally, the map will be
modified against the topographical map and database of
cadastral attributes. The details of each processing module will
be described in the following section.
3. The Proposed Algorithms
Our proposed method for digitizing consists of the following
phases:
a. Vectorization of paper-based map
b. Semi-automatic collinear grouping
c. Specification of corresponding point
d. Non-linear rectification
e. Manual modification
3.1 Vectorization of paper based map
This phase consists of two steps: automatic vectorization and
initial manual modification.
Paper based maps are scanned and vectorized with a system
developed by the author’s group [1]. This system makes use of
mathematical morphology for extraction of line segments and text.
Fig. 1 Overview of cadastral map digitization system
It also has user-friendly interface for manually modify
unsuccessfully processed elements. When existing database of
land information exists, this system can also automatically check
the possible processing or original errors.
The output result is cadastral line segments, the intersection
information, the index line that indicates the position of text string
of cadastral number and arcs that shows the relationship of
separated lands.
3.2 Semi-automatic collinear grouping
The line segments that are likely to be collinear are recognized
automatically by algorithm that is similar to generalization of
chained point list. Each group of collinear segments is given a
unique group number.
Exceptional cases are modified manually through GIS system.
3.3 Specification of corresponding point
Corresponding points with existing topographical map are
manually specified. The top priority for locations of corresponding
points is the boundaries of each area and internal major roads.
3.4 Non-linear rectification
This is the central part of the proposed method and consists of
the following procedures:
a. Generation of TIN with the corresponding points
b. Classification of intersection nodes
