# Math / Coordinates help!

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This is probably NOT the forum for it, but I didn't see another one that better matched..

On a Datasheet, there's occasionally a box with "reference Objects" listed in it. Taken from this datasheet, the box is:

``` CK4224|---------------------------------------------------------------------|
CK4224| PID	Reference Object					 Distance	  Geod. Az  |
CK4224|														   dddmmss.s |
CK4224| CK4225 MILLEN MUN TANK					 APPROX. 4.9 KM 1152117.6 |
CK4224| AB3554 MILLEN LOT						  APPROX. 9.0 KM 1312312.2 |
CK4224| CK5617 ZOMBIE RM 3						  28.981 METERS 13832	 |
CK4224| CK5616 ZOMBIE RM 1						  30.017 METERS 14233	 |
CK4224| CK5615 ZOMBIE AZ MK									   1460148.8 |
CK4224| CK4240 ZOMBIE RM 2						  33.251 METERS 23609	 |
CK4224| CK4241 ZOMBIE AZ MK 2					  APPROX. 0.8 KM 2361037.1 |
CK4224|---------------------------------------------------------------------|```

I'd like to get the coordinates from the distance and bearing, using the mark's points as the base. (To be able to pinpoint the reference objects on a map.)

I found a formulas that helped, but when I do the math I'm off by a certain large percent (i.e. 30meters from the mark I'm off by 15 feet.) That 15 feet really isn't an issue - but when that 30meters is increased to 4.9km, that 15 feet I'm off by grows huge.)

Doing a search, everything I come across is a formula to figure the distance between two known points, which isn't what I need. If anyone can point me in the right direction, would be appreciated!!

Mike.

NGS provides an on-line utility - INVERSE that will allow you to perform the computations correctly.

I'd like to get the coordinates from the distance and bearing, using the mark's points as the base. (To be able to pinpoint the reference objects on a map.)

For that you would want to use the FORWARD program (online or download) at the same link that Dave gave you. INVERSE is when you want to know the distance and azimuth between two known points. FORWARD is when you want to know the coordinates of an unknown point from the position of a known point and an azimuth and distance.

Edited by tosborn

Oops sorry - senior moment - must be the geodetic Altzheimers setting in. I meant FORWARD. Thanks for the correction.

foxtrot_xray -

In addition to FORWARD, there is also Geocalc.

If you want to program it yourself, you will need to use the Vincenty method.

(I don't know whether FORWARD uses the Vincenty method or if it uses something better instead.)

I use GPSTrackmaker for just that.

You just put the math in it and wala you have a distance azimuth and a place to mark a new waypoint at the end of that line and it does the rest.

Fairly simple to do.

Welcome to the world of "precision" benchmark hunting, Mike. It's a step above beating the bushes and guessing. And it's fun (and very satisfying) to work an entire multi-disk station!

I have used NGS FORWARD to calculate the coordinates of dozens of reference marks. The accuracy is awesome. I can go right to the spot, and I've found numerous marks which have been "written off" as missing by others.

The output from FORWARD can be printed directly from the website to create a "data sheet" for the reference mark. The only downside for some folks will be that the coordinates are given in Degrees, Minutes, and Decimal Seconds. If you are accustomed to using Degrees and Decimal Minutes (the format used on geocaching.com), you can do a conversion. However, the easiest thing to do is switch your GPS unit to DDMMSS.S.

The advantage of DDMMSS.S is that the unit reacts to smaller physical movements. For the last few feet, switch off of the "pointer" screen and bring up the coordinates. Move slowly one way and another until the numbers on the screen match the coordinates on the print-out. Then look down at your feet. Chances are you'll be standing on the disk!

-Paul-

``` CK4224|---------------------------------------------------------------------|
CK4224| PID	Reference Object					 Distance	  Geod. Az  |
CK4224|														   dddmmss.s |
CK4224| CK4225 MILLEN MUN TANK					 APPROX. 4.9 KM 1152117.6 |
CK4224| AB3554 MILLEN LOT						  APPROX. 9.0 KM 1312312.2 |
CK4224| CK5617 ZOMBIE RM 3						  28.981 METERS 13832	 |
CK4224| CK5616 ZOMBIE RM 1						  30.017 METERS 14233	 |
CK4224| CK5615 ZOMBIE AZ MK									   1460148.8 |
CK4224| CK4240 ZOMBIE RM 2						  33.251 METERS 23609	 |
CK4224| CK4241 ZOMBIE AZ MK 2					  APPROX. 0.8 KM 2361037.1 |
CK4224|---------------------------------------------------------------------|```

I believe Mike is working on this so that these marks can be added as child waypoints in GSAK, and therefore can be loaded in the GPS at the same time you are loading all the benchmarks.

Question: Which of these PIDs should be created/searched for?

- Do you ever search for the ones with "Approx" distances? And would the coordinate created be anywhere near close enough to be useful?

- The AZ Mark never seems to have a distance -- so even though I like to hunt for these, I don't think there is a way to create a coordinate for it.

Edited by YeOleImposter

I'll echo Paul's comments. I use the FORWARD program to generate coordinates for all the reference disks. It is worth to effort instead of wasting time in the field.

Most written descriptions will include the distance to the azimith mark. While most are only to the nearest tenth of a mile or kilometer, the distance with the geodetic azimuth will generate a point that should get you close. The point, the written description, and knowing that azimuth marks are placed on a high point visible to the tri-station makes the azimuth marks findable without a lot of effort.

Bob

A refinement for those azimuth marks that are at a greater distance (not necessary at 1/4 mile).

Calculate coordinates for a point at the approximate distance and exact azimuth. Set the GOTO on that waypoint, and walk the line where your unit indicates the azimuth or azimuth+/-180 degrees. This will keep you within your handheld unit's accuracy of the proper line, whereas if you do a goto on the tri-station and then look for the az mark you will be limited by the angular accuracy to which you can read the angle on the handheld unit.

I believe Mike is working on this so that these marks can be added as child waypoints in GSAK, and therefore can be loaded in the GPS at the same time you are loading all the benchmarks.

Yeah, I figured that too - that's why I gave him a reference to a Vincenty page.

AZ MARK Suggestion:

As mentioned previously, the approximate distance is given in the narrative. Use NGS FORWARD to calculate a series of coordinates at distances slightly closer and slightly father than that given in the description. This creates a "line" you can walk, with waypoints close to each other. This improves the accuracy over trying to work with a bearing from a station a half-mile away.

Example:

Let's say the description says something line this: "TO REACH THE AZ MK FROM THE STATION, PROCEED WEST ON BRADLEY ROAD 0.4 MILE TO THE STATION ON THE LEFT." I would set waypoints in 0.005/mile increments, from 0.35 to 0.5 miles from the station. Then I walk this line, going from one waypoint to the next, and visually scanning to the left and to the right as I go. (The AZ MK seldom will be exactly on the line.)

What if the description involves a turn onto another road? Check the topo map. Where the bearing line from the station crosses the second road is where you should put a waypoint. Even with muliple turns and large "cross country" bearings, it often is possible to pin down the site of the AZ MARK by looking at the topo map. If there is an aerial photo available, print it and use a protractor to lay out a bearing line with a straight-edge and pen. Often, you can spot a landmark mentioned in the description as your eyes follow the line, and/or as you follow the line in person.

-Paul-

A refinement for those azimuth marks that are at a greater distance (not necessary at 1/4 mile).

Calculate coordinates for a point at the approximate distance and exact azimuth. Set the GOTO on that waypoint, and walk the line where your unit indicates the azimuth or azimuth+/-180 degrees. This will keep you within your handheld unit's accuracy of the proper line, whereas if you do a goto on the tri-station and then look for the az mark you will be limited by the angular accuracy to which you can read the angle on the handheld unit.

Here's a further refinement for finding an azimuth mark I really wanted to find.

The azimuth mark was described as being on the edge of a highway (3/4 mile from the station, in hilly country). Using mapping software, I plotted the published azimuth line and found where it crossed the highway. Then I got the lat long from the mapping software (I was using Google Maps API). I also could tell from the position on the map where the mark was with respect to curves on the road, nearby buildings etc.

With data in hand I found it in 5 minutes.

And here it is:

LX4165 "HOOK MT 2"

Edited by Papa-Bear-NYC

Here's a further note on reference and azimuth marks in general.

In some cases, usually for special marks, I will go to the trouble of calculating all the locations of these subsidiary marks (I also use FORWARD). Now since I have this data, I stick it in my data file which generates the maps that I use (Google Maps API). Here's an example for LX4113 "BUTTERMILK": Map Link

The map shows the station mark in green, the reference marks in blue, and the azimuth mark in yellow.

If I need this for my search, I will zoom way in (try it on the link) and get a detailed map of what is on the ground, print int out and take it with me.

Here's a further note on reference and azimuth marks in general.

In some cases, usually for special marks, I will go to the trouble of calculating all the locations of these subsidiary marks (I also use FORWARD).

I will usually do the same, using NGS forward for the reference marks and calculating positions on topo mapping software for AZ marks. I found/didn't find two back in June based on this method. I recovered the AZ mark for REPUBLIC, RK0474 after plotting a waypoint based on the description (guessing the probable location of the railroad station), the described distance and azimuth. I drove to it and parked my truck 50 feet away from the mark. The station mark and reference marks have been destroyed by an open pit iron mine. If I'd driven to within 50 feet of them, I'd have been sitting under several hundred feet of water.

On the same trip I didn't find the Azimuth mark for IRON, RK0572 but I do know it's not findable. I consulted a 1955 series and found the location, based on the description, then plotted a waypoint. The portion of town the mark was set in back in the 50s was photorevised out of existence on my mapping software due to the expansion of the open pit mine on the site, so I had to go back to paper. With the use of the 1955 topo, I made a waypoint, and confirmed the azimuth mark is destroyed. It's a deep lake now, but used to be a subdivision.

I've used another method to find reference marks on occasions when I've neglected to load coordinates. I'll figure the reverse azimuth (from the reference to the station mark), change my GPS to meters, and do a "find" for the station mark. Before pressing "GO TO" on my Garmin, it displays bearing and distance at the bottom. I'll navigate to a position where the distance and bearing match, and under perfect conditions, I should be standing on the reference mark.

Edited by andylphoto

Thanks guys, especially for the 'Vincenty' link. Yes, it was for the NGSGPX program. I should have the next version soon, which will add reference points as 'children'. Just having to convert PHP into VB. (Luckily, I am familiar with both to not run into any issues.)

Oddly, the first forumla I found (referenced in my first post) was also in PHP, and I was able to get it to appear dead-on, but had to multiply one function by .4143. I dunno why.. <shrug> But after I finish with this, I'm going to run a compare, and see how they match up.

BTW, Georgia DOES have ZOMBIES!

Edited by foxtrot_xray

BTW, Papa-Bear - That is a dadgum nice web interface you got set up!

A refinement for those azimuth marks that are at a greater distance (not necessary at 1/4 mile).

Calculate coordinates for a point at the approximate distance and exact azimuth. Set the GOTO on that waypoint, and walk the line where your unit indicates the azimuth or azimuth+/-180 degrees. This will keep you within your handheld unit's accuracy of the proper line, whereas if you do a goto on the tri-station and then look for the az mark you will be limited by the angular accuracy to which you can read the angle on the handheld unit.

I'm a new user. What are some of the methods you should use when following a GOTO line to a waypoint? I try to pick an object aways away on the intended line and as I walk to it, the GPS (Vista HCx) indicates that I'm +/- the accuracy at that time on either side of the line. If I try to correct for it I wind up zig-zagging. I am using "track up", should I zoom out more to lessen the visual indcation of error?

Thanks,

BTW, Papa-Bear - That is a dadgum nice web interface you got set up!

Thanks foxtrot_xray. I use GSAK as my database from which I generate the data for my web site and maps, so your new version will be a welcome addition.

I like how you get the USGS Topos from online, too. (At one point I had an online script 'hack' that loaded topo and other 'layers' from topozone, but I gave up on it as it didn't benefit me any more than my mapping software.)

BTW, a GPX file created from an entire state (GA), including useable reference points, is 235Megs, up from the NGS dat file of 78Megs.

New version! Posted in other thread..

Me!

Edited by foxtrot_xray

I like how you get the USGS Topos from online, too. (At one point I had an online script 'hack' that loaded topo and other 'layers' from topozone, but I gave up on it as it didn't benefit me any more than my mapping software.)

BTW, a GPX file created from an entire state (GA), including useable reference points, is 235Megs, up from the NGS dat file of 78Megs.

A new version will be coming reeeallly soon.

Me.

The US topos are from the Terraserver which the USGS has licensed to distribut publically (topozone gets there own versions from the USGS). They are in a format that mapping software (like Goglle Maps API and others) can get on the fly. I got the code from a guy here on GC.com who uses it for geocaching. A link appeared a while back to the GSAK forum (which you no doubt belong too) Guy's name is Mark Pelletier. I bet you know him. Really clever code he wrote. Basically a big macro you run from GSAK that creates a web page on the fly (generates all the HTML and JS etc with all the waypoint data). Rather cool stuff.

>ttp://www.topozone.com/map.asp?u=1&lat=36.479291&mapit=Map+It&lon=-94.248494&size=s&s=25&datum=WGS84

=This

Topozone of Coordinates

I think it is something like this.

When,36.479291, 94.248494 a long and latt is added you get the map.

I think you can play with the size and datum it generates as well.

It is on another program I use.

Edited by GEO*Trailblazer 1

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