Author Topic: Latitude and Longitude Readings (Read 17411 times)

George · « **on:** May 21, 2011, 02:01:00 PM »

Just to see what would happen, I took a portable Magellan Roadmate 1700 and my Truck's GPS system. Recorded the Lats and Lons from both then put my HB's GPS in the same area and recorded the lat and lon.

o = Degrees (cannot super script it)

Truck System and Magellan in truck had identical Latitudes and Longitudes
35o 20' 20" N
95o 21' 31" W

Boat - 1197 Humminbird
Fix Type 3D
HDOP 1.09
Est Pos Error 3 ft

35o 20' 21" N
95o 21' 32" W

Both Latitude and longitude were 1" more. 1 second in latitude is worth appx 100 ft. It appears that HBs unit is reading a little off. When I get to a verified position I will try to check it again (do not have one right now).

George

sonar2000 · « **Reply #1 on:** May 21, 2011, 04:41:06 PM »

George......I compared my HB and Lowrance and the Garmin and none of the three were the same. Not much but just a little. Maybe 7 to 12 feet difference.
All were set to WGS84....
Chuck

George · « **Reply #2 on:** May 21, 2011, 06:01:45 PM »

Chuck

What configuration of Lat / Lon did you use? Using Degrees Minutes and Seconds is a broad brush since a second is appx. 88 feet. So the error distance could be anywhere.

If you use a decimal system is it better?

The rules that I knew is that difference in latitude (cannot use Longitude) is used for measuring. A degree = 60 miles, a minute = 1 mile and a second = 88 feet. This was a basic for navigation.

George

sonar2000 · « **Reply #3 on:** May 21, 2011, 07:13:59 PM »

George I compared them in decimal seconds and then in decimal degrees.
I normall use the decimal degrees because the 5th digit of the decimal is 3 feet.
Decimal minutes and seconds are probably more popular until you can get used to the 5 digit decimal.
Most are used to the minutes and seconds for location.
However if it is just for me I use the UTM's. There a meter is a meter is a meter.
It is easier to understand a direction in meters.
For example when going in a given direction it is easy to say go 15 meters instead of 5 seconds.

You are right on your calculations though.
Also on the latitude the curve of the earth and the circumference is adjusted for the location so that the footage is still the same on the decimal positions.

Whew......

Chuck

stillbear · « **Reply #4 on:** May 21, 2011, 07:28:52 PM »

Obviously the GPS manufacturerer with all the modern technology still can't geterdon yet. We the consumer that are
paying the tab for the utmost accuracy to mark and return to a specific area regardless of what GPS unit in our hand or on our dash at the time. I could use a map or word of mouth if I wasn't concerned with accuracy thats why I spend the big bucks. Dealers, Manufacturers, get the picture. Gary

George · « **Reply #5 on:** May 21, 2011, 08:44:24 PM »

The results do not surprise me, as long as the results are repeatable I can work with it. I sometimes use charts to find what I want, but mostly I use my system to find and mark spots. In the U.S. Navy I was a quarter master and navigated with tools (before GPS) that were not nearly as accurate as today's GPS systems. Today's systems allows us to repeatably find the same spots without using landmarks and bottom contours. So I am not disappointed, but I do like testing the systems too see how they compare.

George

sonar2000 · « **Reply #6 on:** May 22, 2011, 02:43:53 PM »

If I only use one particular brand of gps I dont worry because it will always rerad the same gps point so we always are right on target. The only time it gets a bit frustrating is when you give some one else a point or they give you a point and the units are not the same...So we get the variance in position...

Gary....I suppose HB may mean hugh bucks. only guessing... I dont use texting so am not sure of the shortcut meanings....lol....

...

Chuck

Humminbird_Greg · « **Reply #7 on:** May 24, 2011, 03:46:05 PM »

Gary,
You are paying the big bucks for a more accurate GPS system: it is what the government is using. We cannot use the more accurate signal that the military gets to use but that doesn’t mean that we aren’t trying to be more accurate with what we are allowed to use. I’m sure that the next generation of GPS Receivers will be even more accurate but I doubt that you will see a big increase in accuracy. It’s like getting more horsepower out of a motor: up to a certain point you may be able to increase it by many HP but at some point the increases get smaller although as much or more research and resources are being used [did that make sense?].

sonar2000 · « **Reply #8 on:** May 24, 2011, 04:56:26 PM »

I dont see this as a particular accuracy by unit. They all are capable of 1 meter display...The issue is with different manufactures and their presentation of the position. This is where the displays do not agree..One may show a decimal reading of .1 and side by side the next shows .2............or .54532 vs .54534.....
However, units vary widely in the amount of gps satelites they can receive and the speed of processing the signals.
The military removed the built in error position years back and now a days you can expect (unit dependent) anything from 1 meter to 3 meter.
It wold be nice if all units used the same algorithm for display instead of having their own just to be different..
Chuck

Humminbird_Greg · « **Reply #9 on:** May 25, 2011, 08:45:50 AM »

But Chuck that is really getting back to the accuracy of the GPS Receiver now isn’t it? Whether it is a difference in the engine and antennae in the GPS Receiver or the software that goes along with it: what the user sees is the accuracy.

I doubt that you will see everyone use the same algorithms. Not only are these the intellectual property of each company but some of use differ in how we use the GPS data.

The government may have shut the SA signal off (or have they…) back on May 1, 2000 but what I am talking about is the fact that they GPS units can use the encoded PPS (Precise Positioning Service) while we can only use the SPS (Standard Positioning Service) signal. The PPS signal has additional corrections that our GPS Receivers cannot use and so are less accurate than their military counterparts.

I do think that we (Humminbird) and others should add the option to use the UTM and Mercator Meter systems for waypoint coordinates. This would make it easier for those who want/need to use these more accurate systems to exchange, add/delete waypoints from their units. Of course the units and HummPC would have to have built-in converters for this, but hey it’s all just software!

sonar2000 · « **Reply #10 on:** May 25, 2011, 06:49:14 PM »

The number of satelites influence the accuracy. What is different is the unit interpretation of the data and then the selected position for display.
It is not accuracy of the unit or antenna but the difference in the interpretation of various mfg's to decide if they want to display 5.1 or 5.2.
So if you are sitting at a location and you have two mfg's units side by side and the antennas side by side one will read 5.1 and the other 5.2.........you are at the same place only the units tells you differently.
Where this come into play is if you on HB tell me on Lowrance to go to a particular point when I get there it is not the same place and I am off by the decimal difference.
The units are fine just not showing the same data...so as long as you stay within the mfg product you will be on target...
Chuck

Chuck

Humminbird_Greg · « **Reply #11 on:** May 27, 2011, 09:34:22 AM »

I see what you are getting at Chuck but there are some things that you are not considering. While you may be in the same place physically on the face of the earth, the GPS Receivers may not recognize you as being there. Why? Because of the accuracy of the GPS Receiver and the civilian GPS system that we have to use. Consider this:
- All manufacture’s GPS Receivers do not have the same accuracy do to the different engines and antennas being used.
- The unit’s may or may not try and augment this accuracy by some smart programming.

Now if you are talking about coming back to the same physical spot and getting the same exact numbers with the same unit or with another manufacturer’s unit; you have to consider the above plus:
- The same satellites would have to be in the same exact positions (including WAAS satellites), the weather and all other factors that can influence the accuracy of the GPS Receiver would have to be the same for both the day the waypoint was originally marked and on the day that you are trying to find it again.

By the way George, I noticed that your unit was showing a 3D fix type. Where you around any mountains that would have been to the South? I ask because it should have been showing an Enhanced fix type – meaning that you were tracking at least one WAAS satellite.

George · « **Reply #12 on:** May 27, 2011, 11:01:50 AM »

Greg

Tthere are some small mountains, more like large hills a few miles south of me. I did watch the GPS fix go from Enhanced, to 2D and then to 3D within a short period of time.

I live within walking distance of Lake Eufaula in Oklahoma. Lake Eufaula is 102,000 acres with over 600 miles of shoreline. Don't if this means anything.

There are some "GPS waypoints" on the maps I purchased I have put these waypoints in my HB unit. The next time I am on the lake I will check them out. I know what waypoints are and how to plot them on a chart, but sure how these are intended to be used.

George

sonar2000 · « **Reply #13 on:** May 27, 2011, 12:28:19 PM »

On my handheld gps unit I can navigate a specific place each time with an accuracy of 3 feet....regardless of where the satelites are on the horizon. The handheld usually syncs on 6 to 8 satelites.
The only differences I see is when different manufacture units are used. Not so much on handhelds but more so for the sonar/gps combos...
On the handheld I get 3d with four satelites...
Chuck

stillbear · « **Reply #14 on:** May 30, 2011, 07:37:22 PM »

Greg yes that makes since and I agree with you. I guess what I am talking about and what I meant is
A waypoint or a GPS address from my unit is suppose to be accurate . If I give my buddy a address
on a brush pile. He calls me next week ask what i am smoking there is nothing no where around
what do you have to say about that. Or any fixed gps reading on any of the maps are they for all
brands of gps or what are they for. I have a LMS 350 Lowrance on my console along side a 997
and a 1198 on my trolling motor I am going to devote one day to see how all three compare with each other
and how each one separately compare to a fixed gps mark at lake shelbyville. Greg the way i am seeing
this picture right now is your going to be lucky to get two units giving the same exact numbers from
the same place. Gary

sonar2000 · « **Reply #15 on:** May 30, 2011, 07:55:21 PM »

I checked my 1197 for dd mm ss and that is what it displays. I checked my lowrance and it sets dd mm ss.dd....so the two definately do not show the same results. if one unit only shows seconds and the other decimal seconds then there has to be a variance in location...
I will check the exact positions next time out with the two units.
Chuck

Humminbird_Greg · « **Reply #16 on:** June 01, 2011, 11:11:21 AM »

Yes Chuck. If one unit is using a smaller measurement system than the numbers will be different. Where we may round up or down to come up with a whole second; the other company shows decimal seconds so they unit could be off by one second or more if both units decide that they are in different locations on the face of the earth. To compare the two thought I thought that you would have been using the dd.ddddd setting on the Humminbird. I do not know if the other company uses that or something different.

You are correct Gary. With the accuracy of the GPS system that we use and with differences in not only the programming used but also in the GPS Receivers: different units may not give you the same exact numbers from the same location.

George, those hills are killing the possible accuracy of your GPS unit. Any thoughts about moving them?

sonar2000 · « **Reply #17 on:** June 01, 2011, 05:12:44 PM »

Greg, you are right.....I use the dd.ddddd unless it is for a search then we go to UTM. A meter is a meter is a meter in any direction...If you step in a direction in ss how far did you step...
Now if you use seconds then each second is about 88 feet. If you use decimal seconds then each tenth is 8.8 feet. Look at what happens if you use ss.dd (100's of a second...)
Most definately use dd.ddddd. Just ask Mark G......
Chuck

Roddy · « **Reply #18 on:** June 01, 2011, 11:14:48 PM »

Guy's, Were not looking for pin point bombing!!! Just get me within .5 mi and I will find it with SI.

Roddy

sonar2000 · « **Reply #19 on:** June 02, 2011, 10:31:00 AM »

Roddy I agree. get me to within a reasonable distance and then turn on the sonar. That is what it is for...
Fishing might be a bit different but if you can get to within 10 meters you should be able to relocate..
I like UTM anyway...

Chuck

Humminbird_Greg · « **Reply #20 on:** June 03, 2011, 11:17:35 AM »

UTM would make more sense Chuck, even to us non-metric using Americans.

sonar2000 · « **Reply #21 on:** June 03, 2011, 11:52:23 AM »

Yep....a meter is a meter is a meter.
Chuck........

George · « **Reply #22 on:** June 03, 2011, 05:51:56 PM »

Ok guys, I am from an older era, when I navigated I used sextants, dead reckoning, Radio Direction Finders and Loran. What is UTM and what kind of equipment is it and how is it used.

My experience with GPS is that it has always been more then adequate to find the spots that I marked within a few feet.

George

sonar2000 · « **Reply #23 on:** June 03, 2011, 06:08:28 PM »

GPS works fine and is accurate to with in a small margin.

UTM is another way of displaying a position.
Universal Transverse Mercator is position displayed in north of the equator in meters and horizontally in meters east or west of a zone based on 1000 meters segments.
And is dispaly is shown as Z12 328204 E, 47466040 N
Google this and you will find a lot of info especially in wikipedia definition and explaination..
The only reason we ust the UTM is in directing a team to move in a certain direction and amount of distance.
It is easier to say go north 29 meters than to say go north 1 second.

Nothing wrong with the decimal displays if you believe in and trust your equipment.
Chuck

George · « **Reply #24 on:** June 03, 2011, 06:25:52 PM »

Sonar

What kind of equipment do you need for UTM readings?

George

sonar2000 · « **Reply #25 on:** June 03, 2011, 07:05:59 PM »

George, something other than humminbird. HB does not support a position format for UTM...Lowrance, Garmin and the other do..

Chuck

George · « **Reply #26 on:** June 03, 2011, 07:41:02 PM »

WOW, I would think that HB would want to stay competitive, not sure that I need it, but it would be nice to try. Also, not sure I need to over think it, since I am happy with my 1197.

George

sonar2000 · « **Reply #27 on:** June 03, 2011, 08:04:40 PM »

George, I agree, almost every other mfg has a UTM selection. Do not know why HB did not have that written in.
In reality we, in the SAR community here, use a second unit on the water and it is just for position. Ours is a 104c lowrance.
We dont use a great detailed mapping card but rely more on the UTM capability.
Dont read into this as We also feel that decimal degrees is extremely accurate.
We just cant figure out how to walk 20 seconds in a direction..It it not too difficult to move a boat 20 seconds just more so on land for us..
HB seems to be more into fishing although they try to promote a simplified SAR use...
Chuck

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