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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004
overshoot, undershoot, pseudo node, intersection error, etc.) has
been seen and data were ready to create topology in ArcInfo.
Also output DGN file coming from Planicomp-P33 analytical
plotter was imported in ArcView 3.1 directly using CADReader
extension of ArcView (that extends ArcView to support
viewing, querying and analyzing CAD drawings) All the
polygon features were imported as polygon shapes that clearly
shows there is no need for post-processing (i.e. removing
dangles, extending undershoots, etc.) to make closed polygon
objects. Linear objects also were imported to ArcView
environment without any problem.
Error Type Error Description IPCBS’s
[Molkaraei, 1999] Correction
Method
Duplicate Objects that share the same | Puts error
objects start and end points as well as | flag (user
all other points (even if two | must confirm
objects have different linear | for deleting
directions) within the tolerance. | one of those)
Short Any objects (not small texts | Doesn't let to
objects and centroids) shorter than the | draw(or gives
specified tolerance. warning)
Crossing Objects that cross each other| Breaks those
objects with no nodes at crossing. at their
intersection.
Undershoots | Objects that come within the | Extends
and specified tolerance radius of | undershoots
Overshoots | each other but do no meet | and snaps
(Undershoot). overshoots;
Objects that pass each other|generates a
within the specified tolerance | new node at
(Overshoot). intersection 1f
there is no
node.
Clustered Any nodes within the specified | Snaps those
nodes tolerance radius distance of|to centremost
each other. node.
Sliver One segment of one linear | Doesn't let to
polygons feature is located near another, | occur (treats
which they generate a small | those as same
narrow virtual polygon. as duplicate
objects)
Polygon Polygon edges does not reach | Snaps two
closure each other at their endpoints endpoints of
[Neto, 2001] polygon.
Pseudo Any nodes shared by only two | Dissolves
nodes objects. pseudo nodes
and joins two
objects.
Dangling Objects with at least one end | Doesn't let to
objects point that is not shared by | draw (or puts
another object. error flag).
Complex Complex linear objects are | Doesn't let to
linear objects those contain many | draw (or
objects (line | interior vertices fall within the | sends a
weeding) specified corridor tolerance. | warning
(Branching points, dead ends, | message)
and endpoints of polylines are
not generalized.)
Table 1. Cleanup errors and corresponding correction methods
4.2 IPCBS's Efficiency
For comparison between traditional photogrammetric
procedures and using an integrated system like IPCBS, a real
case is chosen. Tehran GIS Center (TGIC) has started to
establish an urban Geographical Information System for Tehran
metropolis the capital of IRAN. Main purpose of this project is
managing Tehran municipality services and implementing the
Master Plan of Tehran. For this purpose, during years 1993-
1995, a project was scheduled and they started to prepare large-
scale maps (1:2,000) of Tehran using photogrammetric method.
This project was schedule according to existing traditional
equipments. So, the main designed steps for producing maps
were:
Planning;
Image reduction (Photogrammetry phase);
Data editing (Editing for cartography and making data
GIS-ready):
4. GIS analyses.
In image-reduction step, raw data were digitized using
photogrammetric instruments while in data-editing step data
were refined to become ready for cartographic or other
purposes. These two steps were the main steps allocated
themselves most of time and costs.
Extracting and drawing of maps by using photogrammetric
instruments started in 1995 and finished in 1997. Editing step
was started at early of 1996 and finished in 1998. After this
step, one project was defined which was called “Organizing of
Maps”. The aim of this project was preparation data for
importing to GIS environments, or making them “GIS-ready”.
This phase started in 1998 and finished in 2001. After all, GIS
analysis and using these data for several applications have
started in 2001. :
While if similar project is designed to be implemented in
feature, we recommend using integrated systems like IPCBS,
because 'data-editing' step and making 'GIS-Ready' step aren't
necessary. This not only reduces the required time for map
production, but also saves costs. Thus, in Tehran case, all of
those five phases can be reduced to three phases and Editing for
Cartography step and Making GIS-Ready step will not be
necessary any more. This investigation shows the benefit of
using integrated system (i.e. IPCBS) in saving time and cost.
UJ h2 —
5. CONCLUSIONS AND RECOMMENDATIONS
5.1 Conclusion
Photogrammetry introduces the fastest, cheapest and most
accurate methods form gathering data, analyzing them and
395
making 3D models. In the other hand, CAD software has many
utilities for viewing, maintaining and data editing (for example
those offer us many viewports, perspective views, precise
measuring of length and area and volume, etc.). Thus in many
applications (e.g. industrial) , integrated systems have shown
their necessities, especially where we may be oblige to prepare
map or 3D model of some inaccessible objects, or where we are
enforced to work in the hazardous environment and other
techniques of data capturing (i.e. tachometry) are useless
[Chapman et al, 1992].
In this research, due to advantages of integration of
photogrammetric systems and CAD systems and in order to
minimize the editing procedure before using data for CAD
purposes or GIS applications, IPCBS (Integrated
Photogrammtric CAD-Based System), a powerful On-line CAD
Based Photogrammetric system were designed. [PCBS
