Member Login  |   Create Account  |   RSS

Subscribe/Renew

HOME

MAGAZINE

Print Subscriptions

Email Subscriptions

Current Edition

E-Edition

Online Exclusives

Submit a Story

Editorial Calendar

Problem Corner

Spanish Magazine

Archives

AERIAL MAPPING

Aerial Mapping Spring 2012

Aerial Mapping 2011

Aerial Mapping 2010

Aerial Mapping Marketing Guide

RED PAGES

Online Directory

Submit or Update Listing

Red Pages Marketing Guide

E-NEWS

Pangaea

Pangaea Advertising

Field Notes

Field Notes Advertising

RESOURCES

Events

Industry News

Partners

PSM Forum

Resource Map

Store

Books

Miscellaneous

Apparel

ADVERTISING

Print

Newsletters

Web

eBlast

Our Circulation

CLASSIFIEDS

View Classified Ads

Place An Ad

View Resumes

Post Your Resume

Classifieds Marketing Guide

sub nav here

Hands On: Transform, by PrimaCode Technologies

Professional Surveyor Magazine - October 2004

James White, PLS

Transform, by PrimaCode Technologies, is a useful tool for using least squares methodologies to find the best fit between multiple sets of coordinates. This utility is a single purpose program, and is run from an easy to use spreadsheet type interface. It provides a way to use a mathematically complex and rigorous solution to quickly and accurately compare data sets.

This program has numerous applications. For example, it can be used to fit field shot evidence to a subdivision map, or to tie into existing survey control. The user must provide at least two sets of coordinates: a target set, whose coordinates will be held, and a subject set, whose coordinates will be adjusted. Each subject set is rotated, translated, and scaled so that its final adjusted coordinates best fit the target. It should be noted that this program operates on coordinates, and not vectors, which makes it different than using least squares for traverse closure or GPS vectors.

Transform provides an "import assistant" that allows data to be imported from a wide variety of data formats. Each set of points is loaded into a named coordinate system, such as "map points," "field shots,"or "control points." The coordinate points for each system can come from the same data file, or from an entirely different source, so that multiple jobs or generations of points can be used together. You can define as many named coordinate systems as you wish, and import coordinates to them.

After the points have been imported into named systems, you then select which system is going to be the target and which is the subject. Next, relationships between the systems are developed. Points from one system are selected and paired with points from another system. For example, point 105 of the target system (an iron pipe found in the field) may be paired with point 508 in the subject system (the common lot corner between lot 5 and 6 on a map). There are two levels of the relationship of the pairs. At the first level you would indicate a pair of points to be inversed and watched. The second level is where the pair of points is linked, which then makes it a factor in the least squares adjustment.

Each linked pair can be given a weight in the adjustment. The weight is indicated by a variance measurement, which reflects your opinion of the uncertainty of the subject system's point. If the evidence you found looks like an original, undisturbed monument, and its uncertainty is very low, you may assign it a variance of 0.02 feet. On the other hand, if it is a wobbly fence post that may have been stuck in by the neighbor last week, then that uncertainty may be two feet. This weighing allows you to control what the program considers important.

Transform's data is displayed in a spreadsheet format. When you link a pair of points, or change the variance/weight of a point, the best fit of all linked pairs is updated to show the relationships (residuals) of all the other paired points. This allows for a quick and effective way to try different fits before deciding 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 software. A transformation is comprised of three components: Rotation, Translation, and Scale Factor. In the case of re-establishing control in an existing subdivision of record, scale factor answers the legal issues of proration against the practical issues of what to do with measuremental error. Transform provides the ability to do it either way, depending on the needs of each particular project. The program will automatically calculate a scale factor as each new linked pair is added. For example, if you are working in an existing subdivision and need to prorate the lots to fit the existing evidence, then scaling does it automatically, but if you wish not to prorate, the scale factor can be disregarded (set to 1.00000). Figure 2 shows the same group of points as Figure 1, but with no scaling.

Transform comes with extensive help and tutorials on the desktop, but no printed manual. The help is organized into subjects, but also has tutorials and a thorough glossary. It is written to aid the user in performing adjustments, without getting to deeply involved in the actual math of the least squares method.

Transform runs on a Pentium PC, and requires Windows 98 or newer (98, ME, NT, 2000, or XP). It also requires the .NET windows extension (a link is provided from PrimaCode's website to install this if needed). For this review, I ran Transform version 1.2.26 and version 1.2.35, on a 3ghz PC running Windows XP, which had .NET pre-installed. The program seemed almost instantaneous in its operation, so I suspect a much lesser machine could be used. Transform requires an Internet connection for initial product registration, but not after that. The software is being updated frequently, so check the website to keep up to date.

There is a free 30-day trial available for download. The software is $500 for the first seat, and $365 for additional seats. The entire ordering process can be handled online where the program 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 program is a fast, accurate tool to get the best possible fit. A session with Transform may take only a few minutes, but allows you to spend your time exploring the relationships in the coordinate data, finding the best points to use, and the best points to discard.
For more information please visit www.primacode.com.

About the Author

James White, PLS
Jim White owns a private practice in Schenectady, New York that provides surveying and software development services.

» Back to our October 2004 Issue

Home  | Privacy Policy  | Contact Us
© 2012 by Flatdog Media, Inc. Articles may not be reproduced, in whole or in part, without prior authorization from Flatdog Media, Inc.

Website design and hosting provided by 270net Technologies in Frederick, Maryland.