Chapter 04 - Using the Trimble Pro-XR/XRS Backpack Unit

The Trimble Pro-XR/XRS units are excellent units for collecting measurements, the XR unit offers meter accuracy before differential correction and the XRS unit can offer sub-meter accuracy in the correct conditions. These units function the same with similar settings, the real difference (which is beyond the scope of this manual) is in equipment and how much information it receives (the XRS makes us of extra measurement data from more sources than just the visible satellites that the XR uses). Here we will discuss how to get the units working, fully charged, in the field and collecting data.

When we receive the unit, the batteries should be fully charged, but it is always advisable to check this out. The batteries are “camcorder” batteries, long thin things used to power some of the larger video recorders, and usually it only takes about four hours to charge four of them. So, just to be safe, we should pop the batteries into the charger overnight prior to leaving for the field. Now that we have charged the batteries, we can connect the cables.

Fortunately, for us, Trimble has seen to it that every part of these units uses a different type of connection, so it is practically impossible to connect parts incorrectly. However, in the interest of efficiency, we will quickly review how everything connects.

First, open the backpack unit to view the cables, this image shows us how things are connected to the GPS unit itself. As you can see, there are a variety of cables running around back here, and it is possible to get a little confused. Let’s take a look at the different parts and what they are used for.

Batteries and Data Logger, these are the cables that we will be connecting the most often. To connect the batteries, place one clip on each battery, these units require two batteries to operate.

The antennae cable (the connection end of which normally exits the backpack at the base of the antennae pole. We will begin by setting up the unit by connecting the batteries, as shown above.

Now, we will connect the antennae, after attaching the antennae support pole(s) to the backpack (these are the yellow metallic poles in the case).

Locate the end opposite end of the antennae cable from the end connected to the GPS unit itself, this end of the cable is usually leading out from a hole in the top of the backpack underneath the antennae mount. Once we’ve found the connector, screw it in as shown and the antenna is ready to go.

Now, locate the opposite end of the Data Logger cable, and connect it to the Data Logger as shown (there are red dots on both the cable and Data Logger to assist in connecting the two).

The Data Logger uses software called Asset Surveyor, and to collect measurements, we must learn how to navigate through this system. However, the software is actually quite easy to use and somewhat intuitive, especially after what we know about GPS from the previous chapters.

The first thing to do is start up the Data Logger, this is best done outside if you want to take points, but can be done indoors if all you want to do is look or change settings.

IMPORTANT – Changing settings can cause problems for other users, if you aren’t sure what the setting you are about to change does, then don’t do it. These units will work with their current settings.

When you first start up the Data Logger, you may see a screen stating that no GPS has been detected There are two reasons for this, one is that you haven’t successfully connected all the cables and the other is you have purposively started up the Data Logger without connecting the cables (we would do this to either change settings or transfer collected data to a computer).

If we are wanting to actually collect data, then we need to check all the cabling (make sure you check the battery cables, since the Data Logger has its own internal battery source and may be working off it), once we are sure that the cables are connected, then we can select Yes. However, if we want to continue using the Data Logger (to make changes or transfer data) then we can hit the softkey underneath No, and continue.

At the startup screen, we can see several selections. To make changes to the settings, we need to use the selection pad to highlight Configuration, and then hit enter. The Configuration menu gives us many choices, many of which we will now review.

Select GPS rover options first We will look at these settings, and maybe make a few changes, that will be up to you. However, since we aren’t the first people to use these units, most of these settings will be fine they way that they are, and if you want to skip changing the settings, that is probably fine. However, if you think that you will need to make a few adjustments, then read on.

The only setting that we will discuss here is the Logging intervals setting. This tells the GPS unit how long to wait between taking readings for a point. For example, to take a point feature, we have to take five readings, and as you can see from above, this unit is set up to wait five seconds between taking readings for a point feature, that means that we would have to wait thirty seconds to take a point reading. That’s not so long really, but we may be rushed for time, and if that is the case, we can select this setting by moving the highlighted area down with the directional pad and then moving right with the directional pad, this will allow us to change the setting.

To finish making changes, simply hit the enter key on the keypad, and the setting changes are saved.

IMPORTANT – Please keep track of all changes that are made to these settings, and kindly change them back to the previous one before returning the unit.

Now, we will take a quick look at the Position filters settings. The only setting in here that we need to worry about is the Elevation mask, which needs to be set no lower than 15 degrees. Also, the PDOP mask can be adjusted, although a setting of 5 should keep the readings accurate enough for most purposes.

The next setting we will look at is the Antennae options, of which the only one we are really concerned about is the antennae height. Its perfectly okay to guesstimate this setting, seeing how the altitude measurement ability of GPS units is still rather questionable (with the notable exception of the RTK units discussed later in this manual). The other settings here are fine and can be left alone.

The next setting which can be set is the Coordinate System, and we should be able to leave that alone seeing as whomever used the unit before us will have probably been using a coordinate system, datum and geoid that are New Zealand specific, you can check these settings if you believe that you will be using something different.

The Map display options allows you specify which layers and files are displayed when you select Map from the main Menu (you can select map from the main menu while collecting points simply by selecting the menu key from the keypad during data collection to see a map of measurements already taken). If you want to compare a previous file with the data that we are currently collecting, we can do that by selecting the previous file in the Background file setting here.

The Units and display settings allow us to determine which units are used for various measurements. Again, since the last person to use this unit before you was probably in New Zealand, you can probably assume that the units are in metric and set appropriately. However, if you need to use units that aren’t commonly used, change them and remember to change them back after you have finished using the unit.

The time and date settings should be correct, check them to make sure as this may affect differential correction at a later stage.

Constant offset is used only if you need to be taking points that are constantly at a different point from where you will be. This will not be covered in this manual, it is rarely needed.

The external sensors settings allows the Data Logger to communicate with other devices.

Finally, Hardware settings will have been set before you use the unit, we will not need to alter any of these settings.

Okay, now that our unit is set up and ready to collect measurements, we might as well get started learning how to use the Pro-XR/XRS to collect data.

The next screen is the Antennae options screen, and since we have already set these, we can just hit the enter button on the keypad.

We are now ready to begin logging features. The first screen we encounter is the Start feature screen, on this screen is a menu showing all the different types of features that are available (as defined by the Data Dictionary). Select the feature by moving the highlighted area around with the motion keypad, and select by pressing enter. We are now recording (logging) measurements. To finish recording (logging) position data for this one measurement, simply hit the enter key again and recording stops.

When you wish to exit data collection, you can do so simply by pressing the Esc key. We have now completed recording data and are ready to transfer this data onto our computer and begin manipulating it.

To transfer data to a computer, all we have to do is repeat the steps for transferring files to this unit, instead of send, we select the receive dialogue.

An Almanac is a file that records position data for the satellites and their trajectories (the path they take through space). To view the data from the Almanac files (which is recorded automatically when you turn on the unit) you must use the Quick Plan utility in the Pathfinder Office software, located under Utilities menu or as a button at the right of the work area.

Once started, the Quick Plan utility window will open along with a menu box, select OK, and you will see the Edit Point Dialogue, which may have a city already listed, if not, select Christchurch from the Cities menu.

Now, you can see many different types of data represented visually by looking under the Graphs menu in the Quick Plan window, explore the different types of graphs. The most commonly used graph is the Number SVs and PDOP, which can show the position, number and accuracy of all satellite accurately for 30 days after the almanac was collected.

As you have probably guessed by now, using this unit as a Base Station is not an overly complex manor. You already have all the necessary skills to make use of this function. To setup the unit as a Base Station, you will need a stationary point for which you know the exact coordinates. Then, it’s a simple matter of telling the unit to behave as a Base Station. To do so, enter the Data collection menu, select Create base file, type in a filename and select enter, adjust the antennae options, select enter and you are creating a Base Station file which you can transfer like any other file type. To stop creating a Base File, simply select enter and confirm by pushing the softkey under yes.

Please refer to Chapter 6 to learn how to use the Base File to differentially correct your data.

Chapter 4 Using the Trimble Pro-XR/XRS Backpack Unit

Chapter 4
Using the Trimble Pro-XR/XRS Backpack Unit