TopoZone Map Inaccuracies

August 10, 2003

I often find that the coordinates given match the cache location (once I get there), but the topo map linked to from the cache page doesn't match where the cache is located.

For instance, This One is shown S (Left hand side, approching from Banner Rd) of the svc road on the topo map, but both of my GPS units (on two seperate days) show the waypoint N of the road.

Of course, I've looked extensively in both areas, and have yet to find this one. I'll be out there again on my afternoon jog today (Sun.), and will look again in the area my GPS says it should be. I'l probably end up smacking my forehead and saying "D'oh! How could I miss THAT".

[This message was edited by Mark 42 on August 10, 2003 at 02:25 PM.]

August 10, 2003

It's hard to say at the time, where errors you may come up with come from. Sometimes the posted coordinates are off by a bit, sometimes your GPS is off by a bit, quite often if you're using Magellans TOPO the map is off by quite a bit. TOPOzone I haven't played with, so I'm afraid I don't know what you can expect from their maps. It all adds up to make it a search, which can be quite fun on occasion.

For determinig the accuracy of the maps, one of the best methods I have found to use the location indexed aerial photos that can be downloaded with programs such as ExpertGPS. You can see a couple of examples of how I've used photo's as a baseline on my webpage, which you can get to via my profile.

About the most accurate maps I've found are the true USGS 1:24,000 scale TOPOs, provided they've been indexed correctly. You'll sometimes find errors on them as well though.

7.4k · August 10, 2003

You need to pay special attention to the "Site uses a different datum so coordinates may be off" notice on the TopoZone link on the cache page. Geocaching.com uses the WGS 84 datum, while TopoZone uses NAD 27. The same coordinates in the two datums can differ by up to around 200 meters.

When I plot the location on a topo map with the correct datum, the cache shows up as practically on top of the road, but on the north side. The aerial photo shows it further away from the road to the north.

August 10, 2003

Ah, that makes sense.

Is there a good way to compensate for that?

Is there a better place for Topo maps (one that uses WGS84)?

It seems like it'd make sense for one system to be the standard.

If I use UTM (on TopoZone, if available) will that bring commonality between the cache listings and the topo maps?

I hope that someday we will be able to put away

our fears and prejudices and just laugh at people.

7.4k · August 10, 2003

quote:
Originally posted by Mark 42:

Is there a good way to compensate for that?

There are some converters around on the web, although the one I was most familiar with I can't seem to find (the one on jeeep.com). This site used to have a link to it, and the fact that it's now gone makes me wonder if they removed the converter.

quote:
Is there a better place for Topo maps (one that uses WGS84)?

Not that I know of, at least not for free. There are several software packages available if you want to spend some money, though. I like to use ExpertGPS. It pulls maps and aerial photos off of the Internet from TerraServer.

quote:
It seems like it'd make sense for one system to be the standard.

WGS84 (World Geodetic System 1984) is for all intents and purposes the current standard. However, since you have a huge catalog of physical maps that were created using older datums, you can't just throw them out. It makes sense for some mapping systems to still use NAD27 (North American Datum 1927), since most USGS topographic maps were printed in that datum.

quote:
If I use UTM (on TopoZone, if available) will that bring commonality between the cache listings and the topo maps?

No. Like latitude/longitude, UTM is a coordinate system, not a datum. UTM coordinates using WGS84 datum are still a different location from the same UTM coordinates using NAD27.

24.7k · August 10, 2003

quote:
Originally posted by Mark 42:
...Is there a good way to compensate for that?

Is there a better place for Topo maps (one that uses WGS84)?...

Sure, use topozone as a general idea of the location. Use your own topo software set for WGS-84 for your planning and to confirm it's on this side of the river and not the other.

You could also translate as has been pointed out.

New datums solve problems the old ones have, but you still have things in the old datum. Such as Topo maps etc. So you need to keep translating.

August 11, 2003

It is easy to get a topo.zone map of a cache using the correct datum.

On the cache page, right underneath the cache coordinates is a link to jeeep.com that automatically converts the coordinates to NAD27

On the jeeep.com webpage, there is a link to a topo map. This will be the correct coordinates.

____________________________________________________

I may be lost, but at least I am making good time.

7.4k · August 11, 2003

quote:
Originally posted by bnolan:

On the cache page, right underneath the cache coordinates is a link to jeeep.com that automatically converts the coordinates to NAD27

Gads, I couldn't find that link to save my life yesterday. Time for me to get away from the computer and out-of-doors!

August 11, 2003

Thaks Y'all!

I appreciate the help.

For the most part, I just use the Topo maps (as someone suggested) to get the general idea. But I need to learn to take a bit more salt with the info when I see something like which side of the road the cache is on according to the TopoZone map.

I'll give the translator a try too. I may end up really liking it, who knows?

I hope that someday we will be able to put away

our fears and prejudices and just laugh at people.

August 11, 2003

http://www.lostoutdoors.com/newmap.html

Quick, free, accurate...except on weekends lately.........Wiz

August 20, 2003

As of today Topozone has changed its format

and is now really BOGUS. You can't display large

maps anymore. Makes it awkward. It's a shame,

that was such a good site, and they have really screwed it up. It was and is in Datum NAD-27,

I generated an Excel formula

that takes a Geocache address like e.g: “N 44° 35.990 W 123° 15.967 (WGS84)”

which you contol-c copy and then paste to the appropriate cell on

your Excel spread sheet to generate a Lostoutdoors map.

Here is the formula:

=("http://www.lostoutdoors.com/map.php?map="&(MID((FIXED((MID((IF((LEN(C4))<34,(MID(C4,1,14))&" "&0&(MID(C4,16,11)),C4)),3,2))+(MID((IF((LEN(C4))<34,(MID(C4,1,14))&" "&0&(MID(C4,16,11)),C4)),7,6)/60),6)),1,9))&",-"&(MID((FIXED((MID((IF((LEN(C4))<34,(MID(C4,1,14))&" "&0&(MID(C4,16,11)),C4)),16,3))+((MID((IF((LEN(C4))<34,(MID(C4,1,14))&" "&0&(MID(C4,16,11)),C4)),21,6))/60),6)),1,10))&"&t=1&z=1&s=1&id=&mark="&(MID((FIXED((MID((IF((LEN(C4))<34,(MID(C4,1,14))&" "&0&(MID(C4,16,11)),C4)),3,2))+(MID((IF((LEN(C4))<34,(MID(C4,1,14))&" "&0&(MID(C4,16,11)),C4)),7,6)/60),6)),1,9))&",-"&(MID((FIXED((MID((IF((LEN(C4))<34,(MID(C4,1,14))&" "&0&(MID(C4,16,11)),C4)),16,3))+((MID((IF((LEN(C4))<34,(MID(C4,1,14))&" "&0&(MID(C4,16,11)),C4)),21,6))/60),6)),1,10))&",255,0,255,7,*&cpos=?810,889")

Copy and paste the geo address to cell C4

Copy and paste this fomula to cell C7 on a blank spread sheet

N 44° 35.990 W 123° 15.967 (WGS84) becomes:

http://www.lostoutdoors.com/map.php?map=44.599833,-123.266117&t=1&z=1&s=1&id=&mark=44.599833,-123.266117,255,0,255,7,*&cpos=?810,889

Lostoutdoors gives you a picture or a map and

it is in WGS-84 Map Datum

August 20, 2003

Oh forgot: concerning that formula always

use "paste special value" (or text) when pasting to the spreadsheet

August 20, 2003

Well, I'll leave it up to you to decide whether we're "bogus" or not, but our new large maps are still 800x600, which ain't exactly tiny.

You also omitted the large number of new features that got added, so take a look around. If you're nice, we might even tell you how to switch between NAD27 and WGS84 coordinates, but not if you're cranky <g>.

- Ed

President and Chief Mapmaker

TopoZone.com

August 20, 2003

Using the TopoMaps, I have compared known lat. x long. locations, and it seems that the WGS84 location is 1/4 inch to the right of the NAD27, at least in California (Sacto and L.A). That's at 1:50,000 scale.

August 20, 2003

In Northern California, I find an error of roughly 300 feet in an East/West direction between NAD 27 and WGS 84. The web site www.lostoutdoors.com uses WGS 84 on its map creation page. You can see your cache's location on both topographic maps and aerial photographs.

August 21, 2003

If you look at your USGS 7.5' topo

you will see the WGS-84 offset as small

crosses in each corner of the map. Most of the

maps were done before GPS was invented and were done in NAD-27.

Here in Western Oregon, the difference

is 310 feet at 260° True

Sure can make things confusing till you get

used to it.

August 21, 2003

quote:
If you're nice, we might even tell you how to switch between NAD27 and WGS84 coordinates, but not if you're cranky <g>.

I tried switching from NAD27 to WGS84 and it switches back to NAD27 when I hit REFRESH. Once it works, it'll be extremely hwlpful.

August 21, 2003

Well, Refresh is supposed to reload the page back to where you started - that's the way it's supposed to work.

Once you switch the datum, the new datum sticks around while you scroll around and recenter the map, which is also the way it's supposed to work.

Why are you making map changes and then hitting Refresh? What do you expect to happen? Thanks for the input.

- Ed

August 22, 2003

I figured making the changes and hitting REFRESH would apply the changes. I just want to see the red 'x' where the WGS84 coords are. Thr REFRESH button is confusing then, why not make it "RELOAD LAST PAGE" since that is what it really does.

August 22, 2003

I see - sorry. There's a difference between "hit[ting] REFRESH" (your browser's Refresh/Reload function) and clicking on the "Refresh Map" button on our page. I didn't realize you meant the latter.

Thanks - we'll fix that problem or maybe move the coordinate display button since it works differently. But the switch to WGS84 coordinates happens immediately as soon as you select it - no Refresh of any sort is required.

But please read my note on the "TopoZone News and Updates" thread to understand what the coordinate display selection does. It does NOT move the target symbol to a new location on the map; you need to change the datum requested in the URL to do that.

August 22, 2003

BTW, the Refresh Map button does NOT reload the last page. It updates the map with any new selections you've made from the Map Source, View Scale, or Map Size settings, so you can make multiple changes and then hit the button.

We'll probably just regroup things so the button's below the options it controls, and leave the other settings (Coordinate Format, Coordinate Datum, and Show Target) below it since those three happen immediately.

August 22, 2003

quote:
It does NOT move the target symbol to a new location on the map; you need to change the datum requested in the URL to do that.

That's what I wanted to know, which is fine because I'm used to looking about 1/4 inch to the right to get the WGS84 location. Maybe we can get Jeremy to change the URL. I noticed on one map I was looking, there was the border of the actual printed map. Are the maps no longer continous from one quad to another?

August 22, 2003

No, the maps are continuous. But the source data got mishandled for some of the smaller-scale (larger area) views. We're fixing it, but right now there are a very few places where the 1:24K/25K maps, when viewed at 1:50,000 scale or smaller, are misaligned. Viewing them at 1:24,000 or 1:25,000 scale should fix it.

August 24, 2003

Well! I started this thread, read it a couple of times, thean assumed it had gone dormant.

Was I ever wrong! It's good to see a company like TopoZone cares enough about its product to answer questions in a forum where many of its users are likely to frequent.

I wouldn't have realized it was active if Schweinhund hadn't been so good as to actually email me info on NAD27 and WGS84 & conversion.

Kudos to y'all!

I too noticed that when I chose WGS84 I thought "refresh map" would make the change happen. I haven't been back to see if it now does, or tried the site armed with some of the info from this thread,

"I'm not Responsible... just ask my wife, She'll confirm it"

August 24, 2003

Well, I went and tried the TopoZone map for the Cache in the link

I gave in my first post... I can't see the target move when

I change from NAD27 to WGS84. It looks like it is forcing itself back to the default NAD27.

It'd be nice if preferences like Map size, initial scale & datum preference were saved for each user (by cookie or account) so that it would start out in the preferred mode.

I'll be watching this thread now though

"I'm not Responsible... just ask my wife, She'll confirm it"

August 25, 2003

No, nothing's being "forced back" to NAD27. If you look at your URL carefully, adding "&datum=WGS84" or "&datum=NAD83" to the URL will make the target location move, since NAD27 is the default.

We already save a number of preferences and settings for our users (that is, for our TopoFactory subscribers) who log in to TopoZone. We'll be doing that for the coordinate DISPLAY datum, too.

But we can't do that for URL links. It's up to the link creator, not the user, to specify what datum is used. Most URLs that link to TopoZone already DO use the correct datum - geocaching.com is unusual in that respect. So if you were to - as a user - set your "preferences" to tell us to make the default datum WGS84, then many of the other sites that link to TopoZone maps would start displaying things in the wrong place.

August 25, 2003

It does work when I paste the appended protion you maentioned, but it doesn't do it from any of the buttons on the website.

I took:

http://www.topozone.com/map.asp?lat=47.4887&lon=-122.5572&s=25&layer=DRG25&size=s&u=1

and changed it to:

http://www.topozone.com/map.asp?lat=47.4887&lon=-122.5572&s=25&layer=DRG25&size=s&u=1&datum=WGS84

and it did work, but it's not very intuitive (if the orifinal had said "&datum=NAD27 in it, I probably would have figured it out, but w/o that, no.)

"I'm not Responsible... just ask my wife, She'll confirm it"

August 25, 2003

Well, if I had known in March, 1999 that I was going to offer different datum options in August, 2003, I would have added the &datum parameter back then <g>.

August 25, 2003

You didn't read my instructions (TopoZone News and Updates). The buttons on the Web site do NOT change the interpretation of the URL parameters. We presume that the passed URL (i.e. a link from geocaching.com or elsewhere) was intended to point to the right place.

As far as I'm aware, every other site that links to TopoZone maps (and there are quite a few) pass NAD27 coordinates and their maps show up in the right place. The geocaching.com links are easy to fix, since they're all consistent (AFAIK).

The controls on the map page govern the DISPLAYED coordinates, not the interpretation of the requested location. There is relatively little value in the latter functionality, and it would add another layer of complexity to an already confusing subject.

August 27, 2003

quote:
Originally posted by Mark 42:
Is there a better place for Topo maps (one that uses WGS84)?

There are lots of places. I gathered them in CacheMaps to be able to click to a map for a cache waypoint right away.

I must admit that TopoZone is not handled correctly with my links also.

Will be updated this weekend

BigBird

August 27, 2003

I hadn't realized that TopoZone wasn't a "stand alone" map site. I didn't know that it was designed primarily to be linked to, rather than just accessed and then have coordinates typed in by hand and a datum chosen to map with.

I would like to be able to use it that way, and now that I know how to append datum selection into the URL I can do it that way, but still that seems not to be the most user friendly approach. Especially if you start at

http://www.topozone.com/

then select "get a map - decimal degrees"

http://www.topozone.com/finddd.asp

There is nothing telling the user which Datum he is using, so if he makes a wrong assumption (like WGS84), the map will be incorrect.

"I'm not Responsible... just ask my wife, She'll confirm it"

August 27, 2003

We've never thought of TopoZone as a site "primarily to be linked to", and the vast majority of the maps we make do NOT come from links.

The Get a Map - Decimal Degrees has used NAD27 coordinates for almost four years now <g>. Nothing's changed.

We are in the middle of making a number of changes to TopoZone, one of which is support in several places for multiple datums. There's no UI for datum selection yet. I posted the info about using datum selection in the URL here since I knew it was a matter of interest on this site (most sites link to us and use NAD27 coordinates). It's not intended to be "user" friendly, it's intended to be "linker" friendly

August 27, 2003

Should the link on each of the cache pages include the "&datum=WGS84" at the end?

The cache I gave the link to in the first message on this thread has a link to a topo map that shows the cache on the wrong side of the road... sometimes when I go jogging I try to find caches with just the compass I wear on a lanyard around my neck (along with a whistle, dogtag, and a key to my car door) and a topo map (printed from the link on the cache's page).

Now that I know what's going on, I can correct for it, but a couple of weeks ago I wouldn't have (and didn't) even recognize that the cache uses a different datum than the map. I just assumed if there is a link to a map of the cache location, when I click on it I'll get the right map.

Is there a way that the owner of the cache can do it (either when submitting the cache for approval, or by editting an existing cache)?

"I'm not Responsible... just ask my wife, She'll confirm it"

[This message was edited by Mark 42 on August 27, 2003 at 03:18 PM.]

5.3k · August 27, 2003

quote:
Originally posted by Mark 42:
Should the link on each of the cache pages include the "&datum=WGS84" at the end?

I'm sure TPTB will change that soon, now that the option exists.

The link to Topozone is just about useless. I don't understand why geocaching.com won't generate the NAD27 coords of the cache for that link, but they don't.

quote:
Is there a way that the owner of the cache can do it (either when submitting the cache for approval, or by editting an existing cache)?

I think that the best solution for you would be to buy a program (such as ExpertGPS or National Geographic TOPO) that automatically does the conversion for you and print the maps from that.

Either that, or use the link to Jeeep.com and link from there to the Topozone map. Just never use the link from the cache page, because it is wrong.

And I wish we could change the subject of this thread, since the errors in question are in the geocaching.com site instead of the topozone site.

August 27, 2003

Actually, you can use the link from the cache...

once the Topozone map loads, paste "&datum=WGS84" at the end of the URL in the Address field and hit enter.

"I'm not Responsible... just ask my wife, She'll confirm it"

4.5k · August 27, 2003

Ed, Is there any way to get the UTM grid lines drawn in at the 1000 meter position? That way you can see where you're at when comparing to the GPS during a hike.

Alan

August 27, 2003

Alan, it's on the "to-do" list. The major motivator behind our technology changes is that we've moved to a very powerful mapping system that lets us do a lot of very nice things. The old server did exactly one thing very well, but there was no hope of adding map features.

I won't promise it *soon*, but 1km UTM grids are definitely well up there on the list!

TopoZone Map Inaccuracies

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