Exploring the world of free tools for GIS, GPS, Google Earth, neogeography, and more.
Part I covered a number of ways to improve the accuracy of GPS position measurements using a standard consumer-grade unit. Here are a few more ways to improve your chances of getting an accurate position determination.
Continue reading ‘Improving Position Measurement Accuracy In Consumer-Grade GPS Receivers – Part II’
Bill Clark, the author of the useful Google Earth Public Land Survey System (PLSS) tool, has a new online app for converting spreadsheet data into point KML files, and opening them directly in Google Earth. Spreadsheet files can be in XLS (Office 2003 or earlier for now, Office 2007 support coming), CSV, or TXT (tab-delimited format); the minimum data required includes only latitude and longitude (either decimal or degree-minute-second formats are acceptable). Optional additional data accepted includes:
Make sure the column headings are included, exactly as specified on the web page’s instructions; there’s an option on the web page to review the spreadsheet data online to make sure it’s correct. The data is formatted into KML at the server, then sent back to your computer to be opened in Google Earth; the original data is then deleted at the server end for security. If you want to save the data displayed in Google Earth, make sure you right-click on the data item in the Places window on the left, and save it in either KML or KMZ format.
My previous post recommended using an external GPS antenna to improve accuracy. They aren’t actually all that expensive – you can pick one up for $20-30 on eBay. But for really cheap GPS antennas, you might try one of my favorite gadget sites, DealExtreme. You can get an external GPS antenna for as little as $7.50, or as much as $8.31, a price that includes shipping from Hong Kong. I have no experience with either model, no specs are given, and the connector description (“F-Cable”) is one that I’m not familiar with, so caveat emptor (“let the buyer beware”). Still, at this price, you don’t have much to lose.
DealExtreme is full of both useful and oddball gadgets, many at absurdly low prices, especially given that all the prices include shipping. Geographically-related, in addition to a few GPS-related items like the antennas, they also have dozens of compasses, from a digital compass with a built-in altimeter and thermometer for about $30, to a twenty-pack of mini-compasses for $2.60. Not to mention the combination butane lighter and compass for $4. Thousands of other items as well, from the useful to the absurd (Mario and Luigi air freshener, anyone?), most at astoundingly low prices. Takes a few weeks for the items to show up, but I’ve never had a problem with any order, including the one item that was out-of-stock (got a prompt refund).
A consumer-grade GPS receiver is very unlikely to achieve the same high level of position accuracy as a survey-grade multi-frequency GPS receiver with post-processing capabilities, at least repeatably anyway. But the former is available for less than $200, while the latter can easily cost thousands of dollars. Sometimes you don’t need the sub-meter (even centimeter) accuracy of the more-expensive unit; sometimes, getting a position reliably within a few meters is good enough. And there are ways you can improve your chances of getting reasonably good and repeatable measurement accuracy even with an inexpensive unit (and some of these help with the more expensive units as well).
Continue reading ‘Improving Position Measurement Accuracy In Consumer-Grade GPS Receivers – Part I’
An earlier post featured a Google Earth KML file by Price Collins that indexed US Army topographic maps (1:250K) downloadable from the Perry-Castaneda Map library. At that time, 435 city maps and 413 1:250K quadrangles had been indexed, with each indexed map reference in the KML file containing a download link to the original map graphic file. Price writes to say that he has finished the index; it now includes 1785 topo quadrangles, covering large parts of Asia, Oceania, and Africa:
Also, 440 city maps; this picture shows those available for part of East Asia
4/26/09: GPStamper is now a commercial program; there’s a trial version that runs for 30 days, and free versions are available for non-commercial scientific work and surveys.
I posted earlier on GPStamper, a handy free utility that takes a geotagged photo and prints the coordinates and time it was taken at on the bottom of the image, saving a copy of it losslessly (no degradation of the original JPG image), leaving the original image untouched. Mike Lee, the author of GPStamper, writes to say that he’s upgraded the program with a few new features:
Continue reading ‘Stamping Geotagged Photos With XMP Location And Coordinates’
While a previous post dealt with using ERDAS Viewfinder to re-project raster images from one coordinate system to another, probably its most useful function, it does also have some other utilities. To start with, it has some satellite image viewing and enhancement capabilities, including multiband display, sharpening and softening, histogram equalization, and two standard deviation stretch. I won’t talk about those here, since I think its capabilities in that area are too limited to be especially useful, and I’ll probably cover more useful satellite image analysis programs in the future, But if you’re interested in those, you can take a look in the help file, or this handy tutorial PDF, which also describes how to use the general toolbar controls to zoom in/out and pan the map.
Instead, I’ll look at two other utilities, accessible from the Tools menu:
For a long time, I thought that the free utility ERDAS Viewfinder 2.1 had slipped through the cracks after the acquisition of ERDAS by Leica Geosystems, but it recently re-surfaced for me in a Google search. And that’s great (thanks, Leica!), because while Viewfinder is an OK geographic image viewer, especially when compared to the many alternatives now available, it does have one very handy capability: the ability to re-project a raster image from one coordinate system to another, and save the new image in GeoTiff format with the new projection/datum data embedded.
Continue reading ‘Reprojecting Raster Imagery II – ERDAS Viewfinder’
