True View 3D imaging System (3DIS) uses Applanix APX Position and Orientation Systems (POS). The POS is a GNSS-aided Inertial Navigation System that provides the precise position and orientation of the sensor at a rate of 200 observations per second. This information is needed to “geocode” LIDAR and determine the exterior orientation of images. Applanix supplies sophisticated software called “POSPac” for post-processing the POS data. POSPac is a rather complex software package so we (GeoCue) have wrapped POSPac (local or Cloud, depending on your business model) within our post-processing software, True View Evo. This reduces POS processing to a simple input wizard.
We provide you with three referencing options for POS post-processing as shown in Figure 1. Let’s have a look at how you would select the appropriate option.
Figure 1 – POS Post-Processing Options
No matter what you may hear to the contrary, the most reliable and accurate reference strategy for drone mapping is to use a local physical base station. This is the “Single Base” option in Figure 1 (it is also the option you would choose if you are planning to use a nearby CORS). The requirements for a True View base station are very low cost – you simply need a minimum dual frequency (L1/L2) static base station capable of recoding an observation session and outputting a file in RINEX format. A full base station that meets this requirement (including pole and tripod) can be acquired for less than US $4,500. Happily, Local Base is the least expensive post-processing option; free if you have a purchased True View system and the lowest tier if you are using a Subscription True View.
The other options, Smart Base and PP-RTX, allow you to post-process without a physical on-site base station. However, you pay for this convenience with a slight reduction in network accuracy as well as increased processing cost. Since you must be on the ground to launch the drone, why not just set a local base while you are at it?
Given the above recommendation, when would you choose Smart Base or PP-RTX? I see two scenarios for this. The first is when you show up on site and you forgot the base station (it happens!) or batteries or they are dead or ….. The second is what I call “base station rescues.” This is where something happened to your base station session, but you do not discover the problem until you have left the site. The “something” can be as simple as a battery going dead during the recording session. Smart Base uses a collection of local stations (for example, from a Continuously Operating Reference Station, CORS) to construct a static virtual base station. Smart Base can only be used where coverage exists (see https://applanixsmartbase.com). Trimble PP-RTX is a precise point positioning solution that is available world-wide. No worries about having sufficient CORS close to your project, PP-RTX can position anywhere.
Thus a good, general reference strategy is:
The very nice thing about a True View ecosystem is you do not need to have an annual subscription to Smart Base or Trimble PP-RTX. Using True View Points from your True View account, you can use these services any time they are needed on an ad hoc basis; you are changed only for the minutes you actually use.
This is what a True View Ecosystem is all about – staying out of your way for normal operations yet offering low friction options when they are truly needed.