APN-039 Rev 2 December 7, 2007

Application Note on Pass to Pass Mode

Introduction

This application note includes background information on the Pass to Pass mode and general guidance

on how to use it.

About Pass to Pass Mode

The Pass to Pass mode

is a method of pseudorange smoothing to keep solutions lined up. This results

in better relative positions over short time periods. Pass to Pass mode is most applicable for machine

guidance applications and is typically used with RTK positioning. For an example, see the figure below.

Figure 1: Pass to Pass Mode Example

Version 3.210 of the OEMV firmware includes the PDP (pseudorange/delta-phase) filter, another solution

smoother. For the smoothest solution, try using both the Pass to Pass mode and the PDP filter.

Both furrows are

off the true line by

the same amount

so that each

subsequent pass

has a relative

position to match

previous passes.

APN-039 Rev 2 December 7, 2007

Test Results

This section describes investigation testing performed on the OEMV family of receivers in Pass-to-Pass

mode with 3.100 software. These tests were done on a rooftop in a static environment. Data was

collected for 24 hours, then post-processed for various pass time intervals. All of the data was collected

with the following command filter settings:

PASSTOPASS enable on on default 1.0.

Data processing starts by computing the cross-track error, relative to a N-S line for each point, in the data

set. For the 15 minute time interval, the RMS (root mean square) cross-track error is calculated using

each of the 900 points in one pass. The same thing is done for the second pass and so on. Once this is

caluculated, there is a single value that can be used to represent each pass in the field. To evaluate how

much variability there is between passes, the single value from each pass is differenced with the previous

pass. The overall pass to pass error is calculated as the mean of the absolute value of these differences.

The test results reveal how much the horizontal position changes over the short time interval, not how

much it changes over the entire data set. All the results in Table 1 and Table 2 are for the horizontal

RMS. The

se results are from using a 15 minute pass interval in post-processing.

Table 1 contains results from tests with an OEMV with L1 only and P

ass to Pass smoothing enabled.

Table 1: OEMV with L1

Test Number of Passes Pass to Pass RMS

Accuracy (m)

WAAS L1 only 95 0.14

CDGPS L1 only 95 0.14

OmniSTAR VBS 95 0.13

Table 2 contains the results from tests with an OEMV3 with L1 and L2 and Pass to Pass smoothing

enabl

ed.

Table 2: OEMV3 with L1 & L2

Test Number of Passes Pass to Pass RMS

Accuracy (m)

WAAS L1/L2 95 0.12

DGPS 95 0.16

RTK 95 0.015

CDGPS L1/L2 95 0.13

OmniSTAR VBS 95 0.1

OmniSTAR HP 95 0.03

OmniSTAR XP 95 0.03

Pass to Pass Command

This command is available on all OEMV-based products with 3.100 firmware or higher.

Command: PASSTOPASSMODE

PASSTOPASSMODE Enable/disable solution smoothing modes

This command allows you to enable or disable different solution smoothing modes. The command filters

include the following:

Command Filters:

APN-039 Rev 2 December 7, 2007

• Pass to Pass smoothing (enable/disable) - enabled by command default

• Deweight passtopass (off/default/low/high) - default by default

• Deweight scale - command default -1.0

The command is disabled by factory default

. You may decide to use it if you want to obtain a smoother

solution. In this case, NovAtel advises that you use the recommendations shown in the example and table

that follow.

Abbreviated ASCII Syntax: Message ID: 601

PASSTOPASSMODE [switch] [measmth] [corrsmth] [deweight] [scale]

Factory Default:

passtopassmode disable off off default 1.0

ASCII Examples

1. To enable DGPS and OmniSTAR VBS:

PASSTOPASSMODE enable on off:

2. To enable SBAS

PASSTOPASSMODE enable on on

Refer to Section 2.4 of the OEMV Family Firmware Reference Manual Revision 5 for more information on

factory defaults.

APN-039 Rev 2 December 7, 2007

Field Field Type ASCII

Value

Binary

Value

Description Binary

Format

Binary

Bytes

Binary

Offset

1 PASSTO-

PASSMODE

header

- - This field contains the

command name or the

message header depending on

whether the command is

abbreviated ASCII, ASCII or

binary, respectively.

- H 0

2 DISABLE 0

switch

ENABLE 1

Enable or disable pass to pass

smoothing mode

(recommended = ENABLE)

Enum 4 H

3 measmth ON 1 Enum 4 H+4

OFF 0

Enable or disable measurement

smoothing mode

(recommended = ON

default = OFF)

4 corrsmth ON 1 Enum 4 H+8

OFF 0

Enable or disable correction

smoothing mode

(recommended = ON

default = OFF)

5 deweight OFF 0 Enum 4 H+12

DEFAULT 1

LOW 2

HIGH 3

Pass to pass deweight mode

(default = DEFAULT)

6 scale scale > 0 Deweight scale

(default = 1.0)

Double 8 H+16

Final Points

If you require further information, regarding the topics covered by this document, please contact:

NovAtel Customer Service

1120 – 68 Ave. N.E.

Calgary, Alberta, Canada, T2E 8S5

Phone: +1-800-NOVATEL (in Canada or the U.S.) or +1-403-295-4500

Fax: +1-403-295-4901

E-mail: support@novatel.com

Website: www.novatel.com