[gps-talkusers] Re: how to deal with multi path in cities

Rita,

I carry a compass some of the time. I mostly use it inside complicted buildings 
but it it can be handy in cities. One of these days, I hope we have a Bluetooth 
receiver with a compass built in.

Mike

At 07:36 PM 6/29/2006, you wrote:
>Mike do you think it is a good idea to have a compass as well as the gps to 
>make sure of accurate direction?
>Rita
>----- Original Message ----- From: "Michael May" <mikemay@xxxxxxxxxxxxxxxx>
>To: <gps-talkusers@xxxxxxxxxxxxx>
>Sent: Tuesday, June 27, 2006 10:46 PM
>Subject: [gps-talkusers] Re: how to deal with multi path in cities
>
>
>>Dave,
>>
>>The location does not vary in terms of its absolute position. You might here 
>>that it is to your left, then to your right. However, it would always be at a 
>>consistent compass direction and the distance to the location would be 
>>reliable.
>>
>>Mike
>>At 06:07 PM 6/27/2006, you wrote:
>>>Mike, if the heading varies during signal degradation, would the location of 
>>>what  ever you are looking for vary as well?
>>>
>>>Dave
>>>
>>>taxation WITH representation isn't so hot, either!
>>>
>>>----- Original Message ----- From: "Michael May" <mikemay@xxxxxxxxxxxxxxxx>
>>>To: "GPS-talkusers-freelists.org" <GPS-talkusers@xxxxxxxxxxxxx>
>>>Sent: Tuesday, June 27, 2006 7:19 AM
>>>Subject: [gps-talkusers] how to deal with multi path in cities
>>>
>>>
>>>>There is one minor down side to the latest super sensative GPS receivers. 
>>>>When you are among tall buildings, it is amazing how well these receivers, 
>>>>like the Holux, report several satellites. The problem is that the quality 
>>>>of those signals is degraded because they are bouncing between the 
>>>>buildings. this is called multi path. The good news is that your position 
>>>>can be tracked but the bad news is that your accuracy and particularly your 
>>>>heading is degraded by this multi path.
>>>>
>>>>You'll know this is happening when you find your direction of travel 
>>>>swinging all over the place. Walk in a constant direction and keep hitting 
>>>>the H key for heading and see if there is any consistency or not. If you 
>>>>see 90 degree shifts in your heading, you are experiencing multi path.
>>>>
>>>>So I ask myself, "Self, what can I do about heading swings?" First, note 
>>>>that the compass direction for your destination will not shift as the 
>>>>compass reading is by definition constent. If your destination is reported 
>>>>as Northwest, that will not change no matter what your relative heading 
>>>>says. You must then rely on this compass direction by either using an 
>>>>actual tactile or audio compass to verify your real heading, or determine 
>>>>your compass direction from the GPS when you are not among tall buildings 
>>>>and keep track of that heading once you are among the buildings. In other 
>>>>words, if the GPS heading is going to be flakey, it is up to you to know 
>>>>the compass direction.
>>>>
>>>>If you know the compass direction, you can then utilize the other 
>>>>information the system is giving you to navigate a route or to use the 
>>>>getting warmer method to get to your destination.
>>>>
>>>>Besides the compass direction, you will want to rely heavily on the 
>>>>distance to your destination or waypoint decreasing. Even if your heading 
>>>>is reported to be South and your Destination is north, if the distance to 
>>>>the destination decreases, don't turn around. A decreasing distance to your 
>>>>destination is something you can depend upon.
>>>>
>>>>This multi path is not something that will vary among receivers or systems. 
>>>>We have tested the $900 Garmin Nuvi receiver against the Holux in this kind 
>>>>of situation and there was no difference.
>>>>
>>>>Until you get out of the tall buildings, pay close attention to that 
>>>>compass direction and to the distance to destination.
>>>>Mike
>>>>
>>>>
>>>>
>>>>Michael G. May
>>>>
>>>>CEO Sendero Group
>>>>
>>>>Developers and distributors of BrailleNote GPS
>>>>Distributing BrailleNote, VoiceNote, Talks, Miniguide, The Tissot Silen-T 
>>>>tactile watch, and the ID Mate bar code reader
>>>>
>>>>MikeMay@xxxxxxxxxxxxxxxx
>>>>http://www.SenderoGroup.com
>>>>
>>>>1-888-757-6810, Fax (530) 757-6830, Mobile (530) 304-0007
>>>>Sendero Group, LLC
>>>>1118 Maple Lane, Davis, CA 95616-1723, USA
>>>>
>>>>Latitude, 38 33 9.239 North
>>>>Longitude, 121 45 40.145 West
>>>>
>>>>
>>>>
>>>
>>
>
>

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