503
ig 2008
INTRODUCE A 1:500 MAP WAS MADE
BY THE IMAGE OF “GOOGLE EARTH” AND ITS SOFTWARE
Ruan Wei
Professor, retired from survey department of Shanghai Tong Ji University - (Ruan wei 65231125@tom.com)
Commission III, WG TTT/4
KEY WORDS: Cartography, Rectification, Photo Map
ABSTRACT:
A 1:500 map was made by the image of “Google Earth” and its software (named five points method) quality of the cartography is
shown on the photo map, it gets great success. Please review it. The experience merits are using only five control points per map. It
depends upon the rectificated model which is precise and strict, surface fitting smooth
1. PREFACE
Forty years of city survey practice is mainly to map by large
scale.
r even a 1:1000 one can be ensured.
We know that Japan has announced its inventory patent which is
called “ The system of map making and the method of map
making” in October of 2000 (P2000-298430A). The purpose of
the patent is obviously to make the city map. However, it needs
more than nine control points, and the accuracy can’t meet the
need of the scaled map mentioned above. It’s not practical.
Can we still put the skill of “GPS + Auto CAD” which keeps up
with the time into practice? The author must answer this
question.
Our successful practice is the best answer. It is practical and
easy.
We use “GPS + Auto CAD” as our main tool, and photo map to
make the map.
Only use five control points for rectification. We successfully
make a 1:500 map by using “Google Earth” image. (The
complete photo map covering 0.21m 2 is available to be
reviewed by e-mail).
It strongly shows that by using aerophotograph with high
resolution, any survey staff can make city map accurately and
without any risk.
That is called “five points method” software which is mature,
reliable, the core of the software design is image rectification
model
2. RECTIFICATED MATHEMATICAL MODEL
The main requirement of the rectificated model is accurate and
easy to operate. Also, the image in two dimensions can be
transferred directly. Only N=5 rectificated control points is
needed for each map. The coordinates of the control points are
not located in a rectangular array.
Most people in our country often feel terrified at the
aerophotogrammetry which is always regarded as a high-tech
job with accurate and expensive equipment. They think it
should be very difficult to master its skills. They also doubt how
the accuracy of making a 1:500 city map o
We know a linear spline which is based upon the small
deflection equation of an infinite beam. Obviously, the surface
spline is a plate of infinite extent that deforms in bending only.
The differential equation relating bending deflection and load of
a plate is
DV 4 W=P (1)
Where
D = flexural rigidity of the plate
W(x,y)= lateral deflect
P= lateral load
Under the following suppose;
1. Deflections are specified at N independent points (x^yO
i=l,N. this requires points loads Pj at these N point. The
values of these loads must be determined to give the
specified deflections.
2. Deflection is a symmetric deflection due to a point load at
the point.
3. The suface spline should become flat a long distance from
the applied loads
Then through complex mathematical analysis, the resulting
equation is rearranged into a form useful for computation.
N
W (x,y) = A + Bx + Cy + E Fj Tj 2 In 2
i = 1
(2)
Where
r| 2 =(x —x,) 2 + (y — y;) 2
Use Eq.(2), we also add three static equilibrium equations to
determine the N+3 unknows.
Use a surface spline to solve it which can achieve good result.
