There are gruelling days where I often ask myself why I became an engineer. But there are better days that far outweigh those days. Days where I am fully convinced that I am in the right place, doing the right thing that suits me. GPS fieldwork days fall into that blissful category.
This month, I was supposed to work on my boss’ personal pet project. It turned out that I had a new assignment. Asthma attacks and schedule disruptions notwithstanding, it was a very fun assignment. I was doing it on my own, there’s a light GPS fieldwork involved, and the client was kind enough to provide me transportation as I do my work for them.
For three days, I was getting rough locations and photos of agencies with the use of a mapping-grade Garmin eTrex handheld GPS. The Nikon GPS camera (AW100) and maps of Lenovo LePad aided me in this three-day navigation from Bicutan to Manila to Makati to Quezon City.I still continue to be amazed with the good resolution and neat GPS functionality of the Nikon AW100.
During college days, GPS was one of my favorite subjects. I got so psyched to do an actual real-life project because most of the field stuff we did in college were confined to UP territory and were administered solely for academic purposes.
Since Google Maps will be the base map for the client, I had to first adjust the parameters of the handheld GPS in the Settings icon. For this particular project, I opted to use WGS84, UTM 51 N. There are so many options for coordinate system and parameters, and this needs to be consistently carried out for all measurements.
I remember what my UP teacher taught me about handheld GPS. It is a known fact that handheld GPS is for mapping only, not for surveying. The survey-grade ones make use of those alien space-ship shaped saucers and tripods, similar to the one we used in Cagayan de Oro project. The error margin for handheld GPS ranges from 15-30 meters. In survey-grade GPS, most of the errors are only in the millimeter range after being processed. Although there may be some signal disruptions that cause noise in the data that need to be taken out during processing.
Satellite signal reception is important during measurement. For a good geometric dilution of precision and also for minimized errors, it is good to have at least 4 good satellite signals in tow. Fortunately for me, Metro Manila has good satellite coverage. I even had 10 satellite signals in one area at a +/- 5 m error margin.
In establishing a point, first you just need to check if satellite signals are good. If the area is urban, is perched on an open area, and is free from obstructions that might jam the signal, your measurements will go unimpeded.
Next, you mark the point of interest and assign a unique and memorable name to it. Save the marked point and double check if the coordinates were saved on the file. A good backup strategy for me is to write down the coordinates for every marked point before I transfer to the next point of interest.
It’s really fairly easy compared to other field activities. The exciting part of it is that you get to watch the GPS unit map your track as you walk or drive from one destination to another.
Garmin has always been one of the more popular choices for handheld GPS and with good reason. However, for survey grade, I think Trimble takes the cake (although the China-made GPS brand Focus is pretty good, too!).
Finally, if you have time, it is best to really browse through the product manuals of the equipment you are using.