@Ron: I have some programming experience too and have been thinking about writing some apps to help with the work I want to do on my property. If I did I figured I would share them with you all and I would be happy to see about making some based on other people's interests. I find programming fun and I have not had the opportunity to do it recently.
Ron Helwig wrote:From what I can tell, current GPS tech is nowhere near accurate enough for what I want to do. It will get you within 3 meters if you're lucky, but I want to be accurate within an inch or two.
It depends on what you are using. GPS tech comes in three broad categories - Consumer, Mapping and Survey grade. Most of us only use consumer grade GPS units (smart phones, tablets, Garmin units from REI, etc.). Survey grade units can get down to mm accuracy, and mapping grade is about a foot. But with consumer grade units there are things you can do to improve its accuracy. If you just need point data many GPS units can take continuous readings over 30sec to a min and then average these readings into a single point. This tends to improve your accuracy a fair bit, and with some programs you can also do this for lines and polygons. Also, there are a lot of variables that can impact the number of satellites that are visible at your location and therefor your accuracy. The obvious is physical objects such as buildings, trees, etc. that will block the line of sight with a satellite. But also the satellites location in the sky changes throughout the day and the number overhead changes too throughout the day. You can use programs such as the Trimble Planning software (free to download and there is an online version) to enter your location information and generate what is known as a PDOP which helps you figure out the best time of day at your location to collect GPS data. The planning software can also tell you what elevation the satellites are in degrees above the horizon at any given time. If your property has a lot of trees than you will want to pick a time of day when the satellites are at their highest elevation. A clinometer can help you determine what is the minimum elevation the satellites need to be in degrees above the horizon for your property. This site goes over how to figure all this out (the mission planning section - but all of the site is helpful):
http://gps.sref.info/course/8a.html I took a GPS course in college that covered all of this and if you are careful to plan when to use GPS on your property you can greatly improve the accuracy. I have gotten consumer grade units down to 3 feet accuracy but of course some units are superior to others and some sites are just bad for GPS (lots of blocking objects). If you pick the best time of day to collect the data for your location and have the unit figure out an average over 30sec to a min for each point you can get some accurate data.
Hope that helps and I hope people keep sharing ideas for apps and sharing existing apps! One web app (also android app) that I like a lot is this one:
SunCalc It is great for looking up the path of the sun at different times of the year and it will also show you the length and direction of a shadow cast by an object of a specific height (you set the height). Great way to quickly see how much shade that new tree or building will cast on your garden!