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).
Looking for a new digital camera (as I am)? You might want to hold off until the new GE models come out this spring. The model E1050 comes with an astonishing list of standard features for a retail price of only $250 (actual street price will likely be even less):
Hope it takes good pictures ;-).
Addendum: GPS yes, but apparently not a standard GPS receiver built in. The Map Room has more info.
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
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’
GPS Tracklog posts about the MiscJunk website, with downloadable high-res topo maps (40-foot contours) for Colorado and Wyoming, with Utah coming next month (February 2008). Other useful stuff as well, including utilities to parse name and location from a Garmin .img format file, and a description of how to create a custom script for an installer that will automatically put a mapset into MapSource (if you’d rather not use MapSet Toolkit). Also, check out the comments in the GPS Tracklog post for a link to free Garmin maps for Argentina, Uruguay and Chile.
