Hands On: Transform, by =
PrimaCode=20
Technologies
Professional Surveyor Magazine -
October=20
2004
James White, PLS
=20
=20
Transform, by PrimaCode Technologies, is a useful tool for =
using=20
least squares methodologies to find the best fit between multiple =
sets of=20
coordinates. This utility is a single purpose program, and is run =
from an=20
easy to use spreadsheet type interface. It provides a way to use a =
mathematically complex and rigorous solution to quickly and =
accurately=20
compare data sets.
This program has numerous applications. =
For=20
example, it can be used to fit field shot evidence to a =
subdivision map,=20
or to tie into existing survey control. The user must provide at =
least two=20
sets of coordinates: a target set, whose coordinates will be held, =
and a=20
subject set, whose coordinates will be adjusted. Each subject set =
is=20
rotated, translated, and scaled so that its final adjusted =
coordinates=20
best fit the target. It should be noted that this program operates =
on=20
coordinates, and not vectors, which makes it different than using =
least=20
squares for traverse closure or GPS vectors.
Transform =
provides an=20
"import assistant" that allows data to be imported from a wide =
variety of=20
data formats. Each set of points is loaded into a named coordinate =
system,=20
such as "map points," "field shots,"or "control points." The =
coordinate=20
points for each system can come from the same data file, or from =
an=20
entirely different source, so that multiple jobs or generations of =
points=20
can be used together. You can define as many named coordinate =
systems as=20
you wish, and import coordinates to them.
After the points =
have=20
been imported into named systems, you then select which system is =
going to=20
be the target and which is the subject. Next, relationships =
between the=20
systems are developed. Points from one system are selected and =
paired with=20
points from another system. For example, point 105 of the target =
system=20
(an iron pipe found in the field) may be paired with point 508 in =
the=20
subject system (the common lot corner between lot 5 and 6 on a =
map). There=20
are two levels of the relationship of the pairs. At the first =
level you=20
would indicate a pair of points to be inversed and watched. The =
second=20
level is where the pair of points is linked, which then makes it a =
factor=20
in the least squares adjustment.
Each linked pair can be =
given a=20
weight in the adjustment. The weight is indicated by a variance=20
measurement, which reflects your opinion of the uncertainty of the =
subject=20
system's point. If the evidence you found looks like an original,=20
undisturbed monument, and its uncertainty is very low, you may =
assign it a=20
variance of 0.02 feet. On the other hand, if it is a wobbly fence =
post=20
that may have been stuck in by the neighbor last week, then that=20
uncertainty may be two feet. This weighing allows you to control =
what the=20
program considers important.
Transform's data is displayed =
in a=20
spreadsheet format. When you link a pair of points, or change the=20
variance/weight of a point, the best fit of all linked pairs is =
updated to=20
show the relationships (residuals) of all the other paired points. =
This=20
allows for a quick and effective way to try different fits before =
deciding=20
which one is best. Figure 1 shows the process of linking points. =
To scale or not to scale? This is an interesting question posed by =
the=20
software. A transformation is comprised of three components: =
Rotation,=20
Translation, and Scale Factor. In the case of re-establishing =
control in=20
an existing subdivision of record, scale factor answers the legal =
issues=20
of proration against the practical issues of what to do with =
measuremental=20
error. Transform provides the ability to do it either way, =
depending on=20
the needs of each particular project. The program will =
automatically=20
calculate a scale factor as each new linked pair is added. For =
example, if=20
you are working in an existing subdivision and need to prorate the =
lots to=20
fit the existing evidence, then scaling does it automatically, but =
if you=20
wish not to prorate, the scale factor can be disregarded (set to =
1.00000).=20
Figure 2 shows the same group of points as Figure 1, but with no =
scaling.=20
Transform comes with extensive help and tutorials on the =
desktop,=20
but no printed manual. The help is organized into subjects, but =
also has=20
tutorials and a thorough glossary. It is written to aid the user =
in=20
performing adjustments, without getting to deeply involved in the =
actual=20
math of the least squares method.
Transform runs on a =
Pentium PC,=20
and requires Windows 98 or newer (98, ME, NT, 2000, or XP). It =
also=20
requires the .NET windows extension (a link is provided from =
PrimaCode's=20
website to install this if needed). For this review, I ran =
Transform=20
version 1.2.26 and version 1.2.35, on a 3ghz PC running Windows =
XP, which=20
had .NET pre-installed. The program seemed almost instantaneous in =
its=20
operation, so I suspect a much lesser machine could be used. =
Transform=20
requires an Internet connection for initial product registration, =
but not=20
after that. The software is being updated frequently, so check the =
website=20
to keep up to date.
There is a free 30-day trial available =
for=20
download. The software is $500 for the first seat, and $365 for =
additional=20
seats. The entire ordering process can be handled online where the =
program=20
is downloaded, or can be ordered as a CD version.
Overall, =
Tranform is a great program for its specific purpose. If your work =
requires you to re-establish control in other pre-existing work, =
this=20
program is a fast, accurate tool to get the best possible fit. A =
session=20
with Transform may take only a few minutes, but allows you to =
spend your=20
time exploring the relationships in the coordinate data, finding =
the best=20
points to use, and the best points to discard.
For more =
information=20
please visit
www.primacode.com.=20
About the Author
-
James White, PLS
Jim White owns a private practice in=20
Schenectady, New York that provides surveying and software =
development=20
services.
=C2=BB Back to=20
our October 2004 Issue