Deviants

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Deviants

Postby Off-track » Wed 19 Jun, 2024 5:53 pm

Playing with UTM grid overlays for tiled mosaic maps (like Basecamp Topo) got me thinking about these maps. The spatial.nsw Topo mosaic is a good test case, because it comes with a UTM grid. The mosaic seems to be built from mapsheets in a UTM projection, but the mosaic is not in a UTM projection. A (1 km) UTM grid is about 10% larger on screen in the South of the state than in the North. And some grid ‘squares’ in the middle are noticeably rectangular. I am guessing that like other mosaic maps (Google Earth, Bing, Garmin?) it uses a variant on spherical Mercator rather than UTM. It is probably inevitable that there are more distortions in a state-wide mosaic than in a 1:25000 map sheet. Maybe we hikers should be less lazy and build a custom map from a select few sheets (pdf or tif) rather than using a small chunk from a big mosaic when we hike near map sheet boundaries? (Light-weight hikers only want to carry one map).

Tom probably knows more about this than I do. His program https://maps.ozultimate.com/archive/08_print/# for NSW has a scale bar that changes size with the grid spacing; but the printed area does not change, so users will get a slightly different map scale depending on latitude.

I don’t care much about scale when there is a UTM grid: as it gives me a 1 km spacing. But (for a backup map) I do care about magnetic declination. This varies across Australia, but those who assume 10º E in the Eastern stares will probably be OK. Those who ignore magnetic declination (assume 0º everywhere) may be in strife. Grid-magnetic variation is more ... variable. Basecamp shows magnetic declination if you choose File>Print, but if you clip and paste (from Basecamp or another mosaic) you need to take care of it yourself; eg write it on your map. Maybe it is possible to code in an arrow or statement of magnetic declination in each map printed from programs like Tom’s?
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Re: Deviants

Postby icefest » Wed 19 Jun, 2024 6:07 pm

I often draw my own magnetic north lines on my maps!
No calculations just read and go!
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Re: Deviants

Postby Off-track » Thu 20 Jun, 2024 6:45 pm

Wise move icefest. I wonder if everyone does (or should do) this? If so, it seems worthwhile for those who provide map-print tools to try to automate (code).
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Re: Deviants

Postby ribuck » Fri 21 Jun, 2024 8:32 am

icefest wrote:I often draw my own magnetic north lines on my maps!

If you're using your phone for the map, why not use the phone's compass? It automatically corrects for grid/magnetic, wherever you are in the world.
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Re: Deviants

Postby tom_brennan » Fri 21 Jun, 2024 6:07 pm

To go into a detailed discussion of projections is probably a bit much for bushwalk.com, and I'm just an amateur map-maker in any case! But I'll try and make a few points.

Firstly, the NSW SS Topo is in projection EPSG:3857 (WGS 84 / Pseudo-Mercator), the same as Google Maps, Bing Maps etc. It is not a "real" projection. From the EPSG remarks:
Not a recognised geodetic system. Uses spherical development of ellipsoidal coordinates. Relative to WGS 84 / World Mercator (CRS code 3395) gives errors of 0.7 percent in scale and differences in northing of up to 43km in the map (21km on the ground).


However, this projection is widely and conveniently used for web mapping, which is why the scale bar changes size. It's programmed to do so.

Secondly, you probably know this, but the UTM grid that comes with the NSW SS Topo is not one UTM grid but three. One of each of the three zones that cover NSW. There is a clear zone discontinuity as it changes from one to the next. For example, just east of Portland, NW of Lithgow.

Off-track wrote:Tom probably knows more about this than I do. His program https://maps.ozultimate.com/archive/08_print/# for NSW has a scale bar that changes size with the grid spacing; but the printed area does not change, so users will get a slightly different map scale depending on latitude.


Thirdly, the printed area in that app will change size but only if you reselect A3 or A4 when you get to your area of interest. If you select A4 near Kempsey, and then move to Cooma, you will definitely get a scale different to 1:25k!

Off-track wrote:Maybe it is possible to code in an arrow or statement of magnetic declination in each map printed from programs like Tom’s?


Coding for magnetic declination is a pain, as while there are declination services out there, they don't appear to be integrated with the main open source mapping tools (Leaflet, QGIS). If that changes, then I'll probably add it.

It's not hard to look up the declination for your area if you need it - the free maps from SS have it listed. The grid magnetic variation only changes by about 3 degrees when you cross a zone boundary (grid convergence goes from ~+1.5 to ~-1.5, varying a little as you go north/south), so you're unlikely to end up in too much trouble if you know the general declination for your area. Keep in mind that declination is only valid for a single point in a map, usually the centre.
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Re: Deviants

Postby icefest » Fri 21 Jun, 2024 9:34 pm

ribuck wrote:If you're using your phone for the map, why not use the phone's compass? It automatically corrects for grid/magnetic, wherever you are in the world.

I'm a funny guy, either paper map and hand-held compass or dedicated mapping GPS.
I like the overview that a larger map gives, so it's easier to plan more complex routes, I don't really trust an electronic compass. There's something about seeing a magnetic compass swing, that given me nice feedback that it's working right. Phone compass just seems more like a guess-o-meter!

I've moved from eTrex to wrist mounted Garmin mapping GPS/watch, almost the same size screen but waterproof, lighter and with much longer battery life.
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Re: Deviants

Postby Off-track » Sat 22 Jun, 2024 8:35 am

Thanks Tom, I learned a lot. Yes, worth including when the technology allows. Ribuck, the paper map and compass is for contingency, when electronics / batteries fail.
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Re: Deviants

Postby rcaffin » Sat 22 Jun, 2024 11:36 am

the paper map and compass is for contingency, when electronics / batteries fail.
May I suggest a slightly different PoV?

The paper map and compass is for real use because electronics / batteries fail.

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Re: Deviants

Postby Warin » Sat 22 Jun, 2024 12:01 pm

rcaffin wrote:the paper map and compass is for contingency, when electronics / batteries fail.
May I suggest a slightly different PoV?

The paper map and compass is for real use because electronics / batteries fail.


The paper map is more useful for a larger view (assuming you are on the paper map and away from an edge). The electronics are easier to find were you are (assuming you have downloaded the relevant area). During the day I usually use the electronics (pros - seed and accuracy), at night/morning the paper map gets looked at, together with any notes (pros overview).
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Re: Deviants

Postby Off-track » Sun 23 Jun, 2024 5:13 pm

It's not hard to look up the declination for your area if you need it - the free maps from SS have it listed.

Actually they don't.

The geopdfs from spatial.nsw have only a statement like "Magnetic North is approximately 11.54°E of Grid North".
Garmin Basecamp (4.7.5) Print has a rose with only TN-MN declination (as an option for which Garmin uses the term magnetic variation).
QTopo geopdfs have a rose with both. Call me old-fashioned, but I prefer the old approach (as still used by QTopo).
Qtopo_rose.PNG
QTopo rose
Qtopo_rose.PNG (23.04 KiB) Viewed 1944 times

The other methods may be more "economical", but the user needs to bear in mind the different choices of the different map suppliers, so I think the risk outweighs the reward.
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Re: Deviants

Postby Off-track » Mon 24 Jun, 2024 10:40 am

And for reasons that I do not understand, QLD and NSW gov mappers have different ideas about the relationship between (UTM) GN and TN in the same region.
Maybe a state-of-origin thing, but confusing (or dangerous) for cross-border hikers in such regions.
TN-GNs.png
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Re: Deviants

Postby tom_brennan » Mon 24 Jun, 2024 4:23 pm

Off-track wrote:Actually they don't.

The geopdfs from spatial.nsw have only a statement like "Magnetic North is approximately 11.54°E of Grid North".


I assume that was a comment on my sloppy nomenclature (they do show the grid-magnetic angle - which is sufficient for navigation - but not the magnetic declination) :D

Off-track wrote:And for reasons that I do not understand, QLD and NSW gov mappers have different ideas about the relationship between (UTM) GN and TN in the same region.

NSW maps are aligned to True North, QLD maps are aligned to Grid North. There's pros and cons of each. For example, the NSW maps have a fixed known extent based on the map code, with no overlap (which can be good or bad!). QLD maps are all a bit bigger to ensure that they cover the area defined by the code, and there is some overlap. QLD maps are rectangular, while the NSW maps are trapezoidal.

In modern day mapping where the maps are computer generated out of one database, I suspect it's probably easier to align to Grid North. In the past maps would have been created individually, and it might have been easier to align to True North.
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Re: Deviants

Postby Off-track » Tue 25 Jun, 2024 10:37 am

Thanks Tom. Very helpful as usual.
But some of the interpretation does not ring true to me.

If the QTopo mapsheets are “aligned to (UTM) grid North” why does each sheet show a grid convergence angle (GN-TN angle) and why does this angle vary between mapsheets?
Are QTopo mapsheets not in a genuine UTM projection, with left and right map edges on a TN-TS alignment, and a rose as explained by USGS (https://www.usgs.gov/faqs/what-do-diffe ... c-map-mean)?
So why do some NSW Topo mapsheets vary so much in alignment from Qtopo mapsheets of the same area? Looking more into this, I think it might be because the NSW mapsheets use a different (Lambert Conformal Conical) projection; even though GDAL (hence QGIS) reports them as UTM. The NSW mapsheets themselves tell us nothing about the projection used, or the direction of TN, and the spatial.nsw websites seem (to put it politely) ambiguous on the topic (https://www.spatial.nsw.gov.au/surveyin ... rojections). But some other sites say that the NSW Topo mapsheets are indeed projected in a flavour of Lambert Conformal Conical (https://www.cbw.bwq.org.au/leaders/QTop ... pingV2.htm).

If this is correct, it would explain why the NSW Topo mapsheets are silent about True (= geographic) North. TN is a moot concept in a Southern Hemisphere Lambert Conformal Conical projection, as the meridians diverge and the North Pole is at infinity in this projection (https://pubs.usgs.gov/pp/1395/report.pdf). It might also explain why the maps are trapezoidal.

In any case, my cautions stand to those who (a) hike across state borders and/or (b) cut and paste backup maps from distorted mosaics. Make sure you record magnetic North on your paper map; and if you need to add a UTM grid, be very careful about projections.
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Re: Deviants

Postby tom_brennan » Tue 25 Jun, 2024 5:12 pm

Off-track wrote:If the QTopo mapsheets are “aligned to (UTM) grid North” why does each sheet show a grid convergence angle (GN-TN angle) and why does this angle vary between mapsheets?


Grid convergence is a function of where you are in a UTM Zone, so it's expected to vary across mapsheets. In the centre of the zone it is 0, everywhere else it is non-zero (except when you are on the equator or the poles).

Off-track wrote:Are QTopo mapsheets not in a genuine UTM projection, with left and right map edges on a TN-TS alignment, and a rose as explained by USGS (https://www.usgs.gov/faqs/what-do-diffe ... c-map-mean)?


Both NSW and QLD maps are in UTM projections. They are printed to different rotations (TN vs GN) and shapes, but those are independent of the actual UTM projection.

See my comment above that the NSW maps are aligned to TN in the centre of the map, but are trapezoidal (though I'm pretty sure that if you were able to look closely enough, the edges are in fact very very slightly curved!!). So the map edges sort of point TN-TS.

The QLD edges point GN.

Off-track wrote:So why do some NSW Topo mapsheets vary so much in alignment from Qtopo mapsheets of the same area? Looking more into this, I think it might be because the NSW mapsheets use a different (Lambert Conformal Conical) projection; even though GDAL (hence QGIS) reports them as UTM. The NSW mapsheets themselves tell us nothing about the projection used, or the direction of TN, and the spatial.nsw websites seem (to put it politely) ambiguous on the topic (https://www.spatial.nsw.gov.au/surveyin ... rojections). But some other sites say that the NSW Topo mapsheets are indeed projected in a flavour of Lambert Conformal Conical (https://www.cbw.bwq.org.au/leaders/QTop ... pingV2.htm).

If this is correct, it would explain why the NSW Topo mapsheets are silent about True (= geographic) North. TN is a moot concept in a Southern Hemisphere Lambert Conformal Conical projection, as the meridians diverge and the North Pole is at infinity in this projection (https://pubs.usgs.gov/pp/1395/report.pdf). It might also explain why the maps are trapezoidal.


No, the large scale maps (1:100k,1:50k, 1:25k etc) for both NSW and QLD all definitely use UTM (or MGA, which has identical parameters)! The alignment is purely due to rotation. GDAL reports them as UTM because they are UTM!!

LCC may be used for some small scale mapping (1:1,000,000 and smaller), but I haven't seen any of it.
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Re: Deviants

Postby Allchin09 » Tue 25 Jun, 2024 10:40 pm

The BOOMI mapsheet example (NSW) is right on the eastern border of the the MGA Zone 55. This is where the variance between grid and true north is at a maximum. If you look at the sheet to the east (BOGGABILLA), you'll see that the grid lines slope the other way, as the grid north to true north variation has flipped from +ve to -ve. When you cross a MGA/UTM zone, this is when you will have a sudden shift of a few degrees in your grid north to magnetic north variation, and this is the thing you need to be careful of.

Now, both NSW and QLD are doing odd things with their variance numbers in this area.

See my notes below, trying to compare maps from NSW and QLD at the border of zone 55 and 56.

What on earth is going on?!
1 - It looks like NSW have updated their magnetic variances for the 2022 edition. However, the value either side of the zone is nearly the same, where as previously it was 2.5d different (as you'd expect when crossing a zone). It almost looks as though they've providing true north to magnetic north variation (despite the text reading "Magnetic North is approximately x°E of Grid North")
2 - The variance diagram on the QLD maps is the same either size of the zone, indicating that grid north is east of true north in both scenarios. This is not correct. It's also not very useful to provide a true north to magnetic north variance on the QLD maps as you can't easily use that directly, and instead would need to calculate grid north to magnetic north. This is more an issue at the edges of zones where the true north to grid north variance is largest.

Zone 55 - NSW - Boomi
2022 - GN to MN = 10.44
2017 - GN to MN = 11.7 (and all online maps prior to 2017)

Zone 55 - QLD - Boomi
TN to GN - 1d19m = 1.32
TN to MN - 8d40m = 8.67
(GN and MN shown east of TN)
In reality, GN is west of TN - this is a mistake in the diagram shown on the map
Therefore GN to MN = 8.67 + 1.32 = 9.99

Zone 56 - NSW - Boggabilla
2022 - GN to MN = 10.59
2017 - GN to MD = 9.2 (and all online maps prior to 2017)

Zone 56 - QLD - Goondiwindi
TN to GN - 1d19m = 1.32
TN to MN - 10d39m = 10.65
(GN and MN shown east of TN)
Therefore GN to MN = 10.65 - 1.32 = 9.33

From Geoscience Australia, on the border of these two maps (E150d / S28d 30m) the true north to magnetic north variation = 10.584
https://geomagnetism.ga.gov.au/agrf-cal ... /agrf-form

Interestingly, a Spatial Services mapping dataset I've just came across (after writing the above), provides the below values as attributes for the maps.
Based on this, it appears that NSW have made an error in the variance statement printed on their maps, it no longer being the grid north to magnetic north variance which used to be printed (and the words which indicate as such) but now the true north to magnetic north variation, ie magnetic declination.

Boomi
GNtoTN 1.32
MagDec 10.42
GNtoMN 11.74

Boggabilla
GNtoTN -1.32
MagDec 10.56
GNtoMN 9.25
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Re: Deviants

Postby Off-track » Wed 26 Jun, 2024 2:09 pm

Thanks Tom and Allchin09. That makes sense. I have not sorted this out as well as Allchin09, but by my estimates the maps I showed (1: 50,000 sheets near Goondiwindi) do match the approximations of Tim Hartley (https://gis.stackexchange.com/questions ... grid-north) and Peter Osborne (https://gis.stackexchange.com/questions ... oordinates) for grid convergence angle (1.3 - 1.4º) at the centre of those maps. The angle is specified as 1.4º on the QLD Bollaranga sheet (in the right direction, unlike the sheet examined by Allchin 09). I measured around that in the NSW Boomi sheet (I can only estimate about +/- 0.25º, even with a big protractor).

Magnetic declination would also be similar: specified as 10.5º (187 MILS) from QLD or calculated as 11.7 - 1.4 = 10.3º from NSW. But what to measure from? Grid-Magnetic variation, given as 11.7ºE from NSW and calculated as 10.5 + 1.4 = 11.9ºE from QLD might be more reliable. Allchin09 made this point well.

For some reason six.nsw gives 2017 Boomi (which I used), whereas spatial.nsw offers 2022 (with new errors noted by Allchin09).

Before Tom’s advice, I had no idea that state cartographers might use different rotations (choice between various Ns) in their Topo mapsheets. Of course even professional cartographers make mistakes (even GDAL makes mistakes); but this rotation is no accident, it is policy.

As a hiker, I can not say which state’s approach is right (though tonight is “state of origin”), but it might be helpful to give the info about projection and rotation on the Topo mapsheets. Hopefully, the other errors noted by Allchin09 will also be fixed in the next release.

My cautions stand to those who (a) hike across state borders and/or (b) cut and paste backup maps from distorted mosaics. Make sure you record Magnetic North on your paper map; and if you need to add a UTM grid, be very careful about projections (and map rotations!). Your preferred mapping software may, or may not, take care of all this for you. It is worth checking, especially if you happen to hike near a UTM zone boundary.
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Re: Deviants

Postby andrewp » Wed 26 Jun, 2024 4:34 pm

FYI here is a web page that calculates the magnetic declination, grid convergence and grid mag angle.

https://www.baysidebush.org.au/trip-program/gridmagangle

Near Lorne (in Vic) the grid convergence is ±1.87, whereas at the NSW/QLD border it is ±1.45 and around the tip of Cape York it is only ±0.55.
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Re: Deviants

Postby rcaffin » Wed 26 Jun, 2024 6:13 pm

You know, when you are deep in Wollemi NP, a degree here or there does not seem to matter very much. Rivers, creeks and spurs matter far more.
The same applies imho most anywhere if you are not trying to lob missiles 40 km. Look at the map, look at the surrounds, and go.

For that matter, some of the old (war time) 1:25k topo maps of Wollemi which we still have to use have some most amusing errors. Iirc, one map omits a major feature entirely (OK, it is right in the corner). Many maps show gentle spurs from the plateau to the river below, while reality is a 40 m high cliff off the edge. A degree or two pales in significance here.

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Re: Deviants

Postby tom_brennan » Thu 27 Jun, 2024 9:28 am

rcaffin wrote:You know, when you are deep in Wollemi NP, a degree here or there does not seem to matter very much. Rivers, creeks and spurs matter far more.


Roger, you know better than to try and introduce common sense navigation into a map nerd discussion :lol: :lol:

Allchin09 wrote:Now, both NSW and QLD are doing odd things with their variance numbers in this area.


That's a bit of a debacle!

At least it seems fairly clear what's gone wrong with the NSW grid-magnetic variation (it's now just the declination). Not sure what is going on with QLD. On a small sample size, the 1:100k Zone 55 maps all seem to have the same declination rose. Same for Zone 54. But the 1:25k maps might be OK? Too many maps to look at...

Off-track wrote:As a hiker, I can not say which state’s approach is right (though tonight is “state of origin”), but it might be helpful to give the info about projection and rotation on the Topo mapsheets. Hopefully, the other errors noted by Allchin09 will also be fixed in the next release.


Based on the SoO result last night, I'd say NSW is right :lol: On a more serious note, the old GA maps used the NSW approach (align with TN). USGS maps are the same.

I doubt the errors will be corrected unless someone reaches out to the relevant Spatial Service. Though in general I've found NSW SS has been fairly pro-active at fixing issues once notified.
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Re: Deviants

Postby Off-track » Thu 27 Jun, 2024 9:48 am

Andrewp, amazing site. I have not checked accuracy but it seems to be useful for the whole of Australia. There must be fancy coding behind it; great work. Could it be even better with a UTM zone overlay, or a labelled UTM grid at high zoom? Does this mean that map-makers can automate inclusion of a MN arrow?

Roger, my old military maps are 1 inch : 1 mile. They have some use in open country, but I would prefer not to rely on them in rainforest. It sounds like you know the Wollemi well. Maybe you even carry a GPSr for backup in new areas.

I can not read 1º on my compass. But I can read 12º (magnetic-grid angle in some areas). When it is raining, I am getting cold, the leeches are climbing up my legs, there are no tracks, the GPSr is not working, I have not been there before and I can not see any landmarks, I have to make the right decisions. I do not want to be 12º off (more than 200 m over 1 km). I do not want to be even 4º off (the angle between grid lines at some UTM zone edges: almost 70m/km). Errors can multiply. But you are right that we should use our eyes and our heads (not just the map and compass or GPS) on the way in as well as out.

Tom, until you helped out I assumed everyone still used True N up (and SOO is 1 all).
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Re: Deviants

Postby tom_brennan » Wed 03 Jul, 2024 9:10 am

I've raised tickets with both QLD and NSW spatial services about the issue relevant to the respective state's maps.

We'll see what they come back with!
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Re: Deviants

Postby tom_brennan » Wed 03 Jul, 2024 1:20 pm

My message to NSW Spatial Services:
I just wanted to point out that the statement of Grid-Magnetic Variation for the 2022 PDF maps downloadable from NSW Spatial Portal, under NSW Topographic Maps, appears to be wrong in the most recent edition of the maps (2022).

For example, the statement for the Lithgow map (2017 edition) is "Magnetic North is 10.4 degrees East of Grid North." This appears to be reasonably accurate (magnetic declination of 12.0°E in 2017, less grid-magnetic angle of approx 1.51°E).

The statement for the Lithgow map (2022 edition) is "Magnetic North is approximately 12.2°E of Grid North". For 2022, the value appears to be correct for the declination (ie Magnetic North is approximately 12.2°E of TRUE North), but the statement is definitely incorrect for Grid-Magnetic Variation.

The issue appear to be consistent across all of the 2022 maps, though I've only checked a sample.

For example, on the Deniliquin map, the Grid-Magnetic Variation is stated as 10.92°E for 2022 but 9.4 degrees East for 2017. The latter is correct. The former is the declination, not the Grid-Magnetic Variation .

The Grid-Magnetic variation is the important one from the point of view of adjusting compasses, so it would be good if the error could be fixed.


And a fairly quick response from Spatial Services:
Thanks you for bringing this to our attention. We will investigate further and ensure that current and correct statements are published in the next version of the maps. Please note that the current catalogue of PDF maps that are available are unable to be altered. If you feel that this error will cause difficulties with navigation please make the relevant allowances or use the older version of the maps where necessary.


I never liked the 2022 versions anyway! The styling is a backward step - which Spatial Services got my views on last year... :lol:
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Re: Deviants

Postby Off-track » Thu 04 Jul, 2024 8:46 am

Thanks Tom. You have done much better than I have with nsw.spatial. (My experience is that bureaucratic minders there intervene to block all information exchange between cartographers and the map-using public). QTopo seems helpful in comparison.

I asked the Qtopo gurus why the current QTopo geopdf topographic maps show a misleading compass rose that follows the USGS model, whereas the earlier sheets showed a rose that correctly identified GN up and gave Grid-Magnetic North angle, as needed for map orientation. Example shown below:
Rose_2003.png
Mt Lindsay 2003
Rose_2003.png (346.81 KiB) Viewed 1190 times

As discussed above, the effect is small at Mt Lindsay (near the centre of a UTM zone) but increases as one approaches the edge of a UTMzone.

I was advised: “Whereas the maps of the 2003 vintage were customised and made individually, in order to generate maps for the whole state and at a variety of scales, we must use the tools that our software supplies. As a result, we don’t have any ability to customise the North roses. However, we will investigate if it is possible to add some clarifying text to the map templates for the next round of maps”.

Some may find fault with the explanation, but at least we can hope for clarity in future mapsheet editions.
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Re: Deviants

Postby tom_brennan » Thu 04 Jul, 2024 10:42 am

Off-track wrote:Thanks Tom. You have done much better than I have with nsw.spatial. (My experience is that bureaucratic minders there intervene to block all information exchange between cartographers and the map-using public). QTopo seems helpful in comparison.


Interesting, I've had no problem with NSW Spatial and I've interacted with them a few different ways. They've been pretty responsive when I've raised data issues with them.


I received a response from QTopo re the declination errors. This is what I sent them:

I was looking at various QTopo maps and it appears that quite a few maps have incorrect Grid North/Magnetic North relative to True North.

For Zone 54 1:100k maps, all four maps I looked at (6564, 7163, 7145, 7140) had identical magnetic declination and grid convergence - 0°34´W for grid convergence and 7°38´E for magnetic declination, for a total grid magnetic angle of 9°12´E. But looking at say 6564 Massacre Inlet, the correct values should be about 4.51°E for magnetic declination and 0.79°E for grid convergence, for a for a total grid magnetic angle of 3.73°E, which is over 5° different. In any case, the grid convergences should change gradually as you go from east to west across the zone, and then sharply when you cross a zone boundary.

The 1:50k maps I checked looked like they might be correct. 7661-2 (Mc Millan Creek) and 6564-4 (Tully Inlet) were both right, as far as I can tell.

The 1:25k maps seem to have a similar issue to the 1:100k maps. The two I looked at (7661-22, 6564-44) both had 1°6´E for grid convergence and 6°4´E for magnetic declination, even though they are on opposite sides of the zone. Neither is correct - the correct figures will be very close to those for the matching 1:50k maps above.

There was a similar issue for Zone 55 - the three 1:100k maps I looked at (7740, 8840, 8240) all had identical magnetic declination and grid convergence. I didn't check the correct values, but not all can be right!

I just wanted to bring it to your attention as anyone relying on these adjustments may be considerably out, and there seems to be a possible issue across a range of maps.


And this is what they responded:

The topo mapping team appreciates you bringing this to our attention and acknowledge it does look like an error on our part.

We will investigate why this occurred and attempt to rectify this when we regenerate our QTopo maps this year.
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Re: Deviants

Postby Off-track » Sat 06 Jul, 2024 8:47 am

In the old days even NSW (or the Cartographic Coy, Aust Svy Corps) used GN up; and they showed a map rose useful for orientation (as well as details of grid convergence and magnetic declination, for those interested, in a box). Here is an example from the 1945 Wallangarra 1 inch sheet:
1945s.png
Wallangarra 1945
1945s.png (163.04 KiB) Viewed 953 times

These days, maps are much better; but cartographers seem to think that map orientation is some kind of bushwalkers' technobabble, and they get confused about TN vs GN. Probably too much screen time as youths.
Sorry about the cut. Does anyone remember Clag Glue or Perkin's Paste, old bed sheets and pinking shears?

Edit: I take it back. On closer inspection this map is TN up! But the rose in the left margin does not show TN (a bit like the text in the current NSW geopdf Topo sheets).
Last edited by Off-track on Tue 09 Jul, 2024 12:45 pm, edited 1 time in total.
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Re: Deviants

Postby johnw » Sat 06 Jul, 2024 11:28 am

Off-track wrote:map rose useful for orientation (as well as details of grid convergence and magnetic declination)

I'm fairly sure some of my older paper maps have that.

Off-track wrote:Does anyone remember Clag Glue or Perkin's Paste

Now you're making me reminisce about primary school in the early 60s! :lol:

Off-track wrote:old bed sheets and pinking shears?

Dunno about old bed sheets but my late mother was a dressmaker, so pinking shears were de rigueur at home back in the day. :)
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Re: Deviants

Postby Off-track » Sun 07 Jul, 2024 9:02 am

Very close John W. The missing link is that we would cut the paper map into 8 equal pieces (hence the cut in the pictured TN box), paste them onto an old bed sheet (to avoid creases in the folded map) and pink around the edge (to minimise fray). It probably did not help our bearings, but we also had topography as stressed by Roger C above. There was even brush-on water repellent, so the result was much more robust in the field. A bit more weight, but ability to carry a heavy pack was a badge of honour back then (or so we foolishly thought). All before computers, mobile phones and GPS of course. Yes, 1960s +/- a decade or so.
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Re: Deviants

Postby MattS » Mon 08 Jul, 2024 10:57 am

Hi all that have posted. Some may seen I've posted in the past on anything related to QTopo. Full disclosure: I run the QTopo program, amongst other mapping work. But anything I post here shouldn't be considered official communication from my Department or Qld Government.

A couple of you, I've seen your feedback come through the channels and you've received my responses (albeit a little paraphrased by our customer service team).

Happy to clarify things a little further here is you feel it would help.
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Re: Deviants

Postby Off-track » Tue 09 Jul, 2024 11:30 am

Thanks MattS, clarification from an expert would help a lot.

Firstly, from what I can see in old mapsheets, all 'old topographic or topographic survey' sheets (from Svy Corps, Natmap, Sunmap or NSW Gov) were laid out on lon-lat edges, so they were TN up. Of course some government mapping (like Forestry and National Parks Departments) used a different rotation entirely, and it varied a lot between maps, but this was usually fairly obvious from the grids (if present) and the compass roses (which on my maps were always present). But maps in the Topo series were always TN up.Then it seems that things changed with QTopo. Now the Topo geopdf mapsheets do not seem to be laid out on lon-lat edges. They do not seem to be TN up. Rather, as Tom B pointed out, they appear to be GN up. But NSW still uses TN up. If that is correct, can you say when and why the States diverged in this matter (without warning that I can see on the mapsheets)?

Secondly, I thought (wrongly it seems) that the longest line on a map compass rose would warn us of map orientation. Can we take anything from the relative length of lines in a Topo map compass rose?

I reckon that ability to correctly orient a paper Topo map in the field is important. Some of the old Topo mapsheets went to a lot of trouble to make this possible (see the example of the Woodenbong 1969 1:50K map below), but anyone who prints a custom map from a web-server these days may need to do it themselves, as described by icefest.
Rose&Text.png
Rose&Text.png (160.78 KiB) Viewed 625 times

After looking at a lot of maps (old and new) the best advice seems to be that no matter when or whence your map came, make sure before departure that it includes an accurate MN line. (If a MN line or angle is provided, check it against Geoscoence Australia https://www.ga.gov.au/scientific-topics/community-safety/projects/agrf or the link given by andrewp. If they differ, check - there can be errors as highlighted by Tom B and Allchin09). Is there better advice?
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Re: Deviants

Postby tom_brennan » Wed 10 Jul, 2024 11:51 am

Off-track wrote:Firstly, from what I can see in old mapsheets, all 'old topographic or topographic survey' sheets (from Svy Corps, Natmap, Sunmap or NSW Gov) were laid out on lon-lat edges, so they were TN up. Of course some government mapping (like Forestry and National Parks Departments) used a different rotation entirely, and it varied a lot between maps, but this was usually fairly obvious from the grids (if present) and the compass roses (which on my maps were always present). But maps in the Topo series were always TN up.Then it seems that things changed with QTopo. Now the Topo geopdf mapsheets do not seem to be laid out on lon-lat edges. They do not seem to be TN up. Rather, as Tom B pointed out, they appear to be GN up. But NSW still uses TN up. If that is correct, can you say when and why the States diverged in this matter (without warning that I can see on the mapsheets)?


From personal experience, it's easier to auto-generate maps aligned with your (grid) projection. For example, I did try to generate a UTM map aligned to TN out of QGIS, and couldn't get it to work. Whereas it's pretty straightforward producing maps aligned to the relevant UTM grid.

Off-track wrote:Secondly, I thought (wrongly it seems) that the longest line on a map compass rose would warn us of map orientation. Can we take anything from the relative length of lines in a Topo map compass rose.


I don't think you can. The old NSW topo maps had the GN line as the longest, but were oriented to TN. The current QTopo maps have the TN line as longest but are oriented to GN. :lol: You'd be happy with the current USGS maps - aligned to TN, with TN line as longest (and aligned with map).

MattS wrote:Happy to clarify things a little further here is you feel it would help.


Thanks Matt - I'm just happy if it gets fixed in the next release!
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