v20180710
Details on SP20 Accuracy

Adding Higher Accuracy to an SP20

You can add additional accuracy to the SP20 at any time. There is no price penalty for purchasing a base unit, then adding accuracy at a later time.

However, you will want to purchase the final accuracy that you need because there is no intermediate step. For example:

If you purchase ‘Sub Meter 30-30 $1,500’ and then at a later date decide to purchase the ‘CM $5,100’ you will have wasted $1,500: there is no option to go from '30-30' to 'cm'.

For this reason, if you are not sure about which accuracy you would like to purchase, we strongly recommend that you ‘rent’ an accuracy for 1-month. The monthly rental price is 10% of the full option price.

 

RTX Subscriptions

If you plan on using an RTX Subscription (about $2,000 per year) you do not need to purchase any additional accuracy options. When RTX is activated, the SP20 will achieve maximum RTX accuracy no matter which accuracy option is enabled.

This means that the base SP20 model will be just as accurate using RTX as the 1 CM model.

The expected accuracy of the SP20 using RTX corrections in the USA is 4 cm CEP.

The advantage of RTX over a RTK network is: 1) no cellular connection is required; 2) it works nationwide. A possible disadvantage of RTX is the convergence time (probably about 20 minutes); this is the time from when the receiver starts getting L-Band corrections until the stated accuracy if achived.

For additional information on RTX click [ RTX Information ]. A one-time, 3-day RTX demo is available [ RTX Demo ]

 

Post-Processing MobileMapper Field

There are two post-processing options. The first option:

680547-51 Post processing option for MobileMapper Field Android 495.00

enables raw data recording in MobileMapper Field. It is installed with a single use POPN code on the receiver and is attached to the receiver. This raw data is un-dithered and can be processed in MobileMapper Office.

The free version of MobileMapper Office will process raw files to decimeter level. The second option:

116128-01 MobileMapper Office cm post-processing option 895.00

enables MobileMapper office to post process down to 1 cm accuracy. This option is applied to a single office machine with a unique POPN code and is not transferable.

 

SBAS (WAAS) Expected and Observed Accuracy

The standard receiver with no accuracy enhancement options enjoys the legendary Blade SBAS engine. The SP20 engine is specified as producing 50 cm horizontal 2Drms and 85 cm vertical 1-sigma results using EGNOS/WAAS. It is our experience that the Blade engine has much better performance in the United States using WAAS than can be obtained in Europe using EGNOS.

The SBAS/WAAS performance is not dithered by the accuracy option. So if you are only going to use WAAS corrected readings, you should not purchase the higher accuracy options.

Using our testing robot in moderate urban canopy [ click for video ]:

with WAAS corrections set to dump the receiver, then wait 30-seconds for signal acquisition, then storing a single epoch reading, we repeatedly get results like this:

Over a 264-minute (4 hours 24 minute) period, encompassing 316 dump cycles, the receiver had a 0.266 meter 1-simga 2D horizontal deviation about the average position. In other words "we expect the two dimensional, horizontal error to be within 0.266 meters, 68% of the time."

Over this same testing period a total range of 1.38 meters in the X, 2.70 meters in the Y direction; or +/- 1.6 meter horizontal range about the average location was observed. The height standard deviation was 0.74 meters with a range of 3.9 meters.

Remember that this is a full signal reacquisition between measurements in moderate urban canopy with a 30-second acquisition time allowance which is representative of real-world use. The SP20 will have substantially better results in wide open conditions, however wide-open testing is not representative of the results you can obtain in real-world applications.

Also remember that when using WAAS corrections, the reported position is IGS08 framed--not NAD83.

This is slightly better than we would expect with the CHC LT500T or the legacy Spectra Precision MobileMapper 120 receivers. For reference, this is about 8 to 10 times better than we observe with the built-in GNSS receivers in modern cell phones.

 

RTK Accuracy

The SP20 when enabled for the best accuracy is a fully-featured multi-frequency, multi-constellation receiver. The engine / antenna combination achieves very fast fixes and has survey accuracy (1 cm) with a network solution.

Depending on the accuracy option that is installed on the receiver, the accuracy may be dithered about the true location:

Standard: The RTK reported horizontal position will be reliable to 1-meter. This is still better than WAAS because: 1) no reported measurement will exceed 1-meter in error; 2) the result will be in the same frame as the correction source, typically NAD83 2011 2010.0.

30cm/30cm: The result will be within 1 foot (peak-to-peak / maximum error).

7cm/2cm: The result will be within 0.23' horizontal and 0.07' vertical.

cm: The result will be undithered, full RTK accuracy.

Flying-RTK

The SP20 has Flying-RTK enabled. This means the SP20 will have amazing results with very long baselines. (Baseline is the distance from the receiver to the source of corrections.)

For example, a fully enabled SP20 located at our office in Salt Lake City receiving RTCM3.0 corrections from the CORS station in Kemmerer Wyoming (165 KM) typically has measurement range results like these:

   X Avg  427442.023  Min  427441.958  Max  427442.127 Rng       0.169  StdDev       0.030 
   Y Avg 4509830.987  Min 4509830.906  Max 4509831.073 Rng       0.167  StdDev       0.022 
 dXY Avg       0.032  Min       0.008  Max       0.132 Rng       0.123  StdDev       0.020 
   H Avg    1310.185  Min    1310.016  Max    1310.633 Rng       0.617  StdDev       0.096  N        5723

For 5723 consecutive measurements (1 hour 30 minutes) the 2-D CEP (1-sigma) is 2 cm with an absolute range of 0.125 meters. This means that a single CORS station can service 100 mile radius area with a 1/2 foot expected range of measurements.

 

SP20 Pitfalls

Base/Rover Pair: Since the SP20 does not have the ability to be used with a UHF radio, the SP20 is unsuitable for use in a Base / Rover pair configuration. While it is possible to push Base corrections to a internet server a cellular connection will always be required for SP20 RTK use.

Traditional Survey Applications: The available Android survey solution (Survey Mobile) may not be as full featured as other WinCE and Win10 survey applications. Integrated support may not be available for robotic total stations and peripherals. Because you can evaluate the Spectra Survey and MobileMapping applications on any Android device, it is easy to verify features and workflows prior to purchase.

 

Summary

The SP20 simultaneously fills several segments of the mobile-mapping/GIS and survey GNSS toolset. The base unit is as accurate as any other GNSS based, WAAS corrected instrument at a better price-point. Because the data-collector is built-in to the SP20, when fully enabled for the highest accuracy the SP20 competes well with traditional GNSS survey instruments at a better price-point.

 

iGage Mapping Corporation
1545 South 1100 East #1;  Salt Lake City UT 84105 USA
Voice:
+1 801 412-0011 Fax: +1 801 412-0022
email
orders@igage.com   General iGage Information