Do you still need to differentially correct GPS data now that Selective Availability (SA) has been turned off by the military?
Yes. GPS without differential correction or post processing can still have up to 25 meters of error in the open without correction. Where most professional grade GPS units can achieve 5 meters and better with post processing or real time differential.
Do I need real time differential correction?
No. But with WAAS capability and the low cost of real-time, it makes more sense today to have this capability. Real time is required some cases. These cases include navigating back to a location with a high degree of accuracy or calculating with accuracy the number of acres in an area. The other reason to have real time correction would be if the user did not have an Internet access or access to a base station to retrieve post-processing files. In addition, real-time correction eliminates one more step back in the office.
How accurate can GPS be?
Dual Frequency GPS systems can achieve real time accuracy of 1 cm and 5 mm with post processing on baseline distances of less than 10 kilometers. These systems require a base station sitting on a known benchmark and a rover unit that obtains the location of the items being mapped. These systems can expedite large surveys. The limitation is that these systems do not work under canopy. These systems can cost between 35 and 75 thousand dollars.
How accurate can acreage estimates be from aerial photographs?
Depends upon whether the photo has been rectified or not (tied to real-world coordinates and the distortion removed). A non-rectified photo can produce inaccuracies of 10-20% in acreages. A good rectified photo can be very accurate. But this totally depends upon the end-user digitizing a subject stand correctly.
In Forest inventories, can you navigate to sample plots?
Yes, the RTI system makes this possible with on-screen mapping capabilities and direct links to T-Cruise for Windows CE. Finally, the GPS and the field data collection program can reside on the same field computer and the software allows for data linking between the two.
Why is spatial plot data important?
Spatial plot data gives us the ability to quickly analyze different variables collected in the cruise data such as volume, value, species distribution, products, environmental factors, etc.
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