Incorrect altitude data

eldron · June 06, 2021, 17:24:23

Hi,
on a recent hike I came across some incorrect altitude data in the map contour lines and also in the srtm data. I noticed this because according to the map the path that we were on should have dropped from around 400m altitude to around 230m within a distance if 100m - which would have been a pretty steep drop. But in reality this was not the case.
When we got home I had a closer look and the first thing I did was to update the map, as it had been 4 years old. But the new map contains the same mistake.
I have also set locus to always display the altutide in the screen center, which was also wrong. So i renamed the srtm folder and re-downloaded the srtm files (via map download and also via the point details screen) - again, the altitude was still wrong.
So I downloaded openandromaps map of that region and I was surprised to see, that the contour lines in the openandromaps where correct.
I have attached two screenshots - the first screenshot shows the correct contour lines (openandro map) and the second shows the incorrect contour lines (locus map). The altitude info (red number in the center) is incorrect on both screenshots, as it´s using the srtm data which is also incorrect.
So I was wondering if this might also apply to other regions and why openandromaps has the correct data, even though both maps are based on openstreetmap data?

freischneider · June 06, 2021, 18:59:07

von wann war deine LoMap und von wann ist die OAM.

eldron · June 06, 2021, 20:45:47

The locus map I used during the hike was from 2016, but when I got home i purchased the latest Locus map of the region to double check, so that one was up to date. The Openandro Map was also up to date, as I downloaded it the same evening to compare it to the locus map.
According to the map details in locus the locus map is from the 27.04.2021 and the Openandromap is from the 30.04.2021 . In both cases it´s the "Sachsen-Anhalt" map.

Graf Geo · June 06, 2021, 20:53:04

Habe gerade geschaut. In OAM werden die Höhenlinien in der Germany_North_oam.osm.map genauso falsch bzw. ungenau angezeigt.
In der Bundesland-Karte sachsen-anhalt_oam.osm.map aber richtig wie in deinem Screenshot.

In den LoMaps ist es leider in beiden Karten falsch/ungenau (Germany north und Sachsen Anhalt). Jeweils aktuelle Versionen.

Da scheinen die LoMaps tatsächlich zu schwächeln.

English (Deepl.com):

I have just looked. In OAM, the contour lines in the Germany_North_oam.osm.map are displayed just as incorrectly or inaccurately. In the state map sachsen-anhalt_oam.osm.map, however, it is correct as in your screenshot.

In LoMaps it is unfortunately wrong/inaccurate in both maps (Germany north and Saxony-Anhalt). Both are current versions.

The LoMaps seem to be generally inaccurate.

Graf Geo · June 06, 2021, 21:01:27

OAM zeigt Höhenlinien in 10 m - Abstufungen, LoMaps nur 25 m. Scheint überall so zu sein.
Ein Grund mehr, weiter OAM zu verwenden. Due gefallen mir eh etwas besser, auch vom Layout und aufgrund der besseren Konfigurierbarkeit bei den Themen.

freischneider · June 06, 2021, 21:02:28

Bei der Genauigkeit der Höhendaten tut sich ja immer wieder was. Die genauesten Daten sind normal von Sonny. Ich verfolge seine Update genau und ein Bereich den ich habe dabei ist lade ich diese gleich herunter. Er schreibt Update normal auch ins Forum von Locus und OAM. Beide verwenden so weit ich weiß für Karten seine Daten. Nun kommt es drauf an ob die neuesten Daten bereits in der Karte berücksichtigt sind. Alle 3 Karten von den gesprochen wurde habe unterschiedliche Update Intervalle.
Am besten du wartest bis zum nächsten Update und wenn der Fehler dann noch vorhanden ist, meldest du diesen im Helpdesk. https://help.locusmap.eu/

freischneider · June 06, 2021, 21:04:01

Quote from: Graf Geo on June 06, 2021, 21:01:27
OAM zeigt Höhenlinien in 10 m - Abstufungen, LoMaps nur 25 m. Scheint überall so zu sein.
Ein Grund mehr, weiter OAM zu verwenden. Due gefallen mir eh etwas besser, auch vom Layout und aufgrund der besseren Konfigurierbarkeit bei den Themen.

ich benutze auch nur OAM Karten. Die Lomap habe ich nur wegen der Offline POI.

Graf Geo · June 06, 2021, 21:14:26

Quote from: freischneider
ich benutze auch nur OAM Karten. Die Lomap habe ich nur wegen der Offline POI.

Die offline POI habe ich sogar alle wieder gelöscht. Der Infogehalt der OSM POI ist meist sehr gering, daher nutze ich die so selten, dass die mir online reichen. Aber das ist ein anderes Thema.

eldron · June 06, 2021, 22:16:27

I actually checked sonny's website to download his srtm files to see if they are correct, but couldn't find any files for the area. But that might have been my bad, i find his website quite confusing.
I wouldn't mind using the openandro map, but the problem is that I really like the map shading and that depends on the srtm altidute data and not the map data. As you can see on the openandro screenshot,the contour lines are correct, but the hillshading is off, as well as the screen center info.
It's a real shame that there's no proper altitude data available for Germany, other countries are doing a much better job at that.

Sonny · June 07, 2021, 10:12:17

Download version "DTM Germany 1" v1 by Sonny" from https://data.opendataportal.at/dataset/dtm-germany (you can just download the files of the area of your interest, e.g. N51E011.zip )

LIDAR elevation files for the area of Sachsen-Anhalt have been added some months ago, probabaly that's the reason why LoMaps still using older (=SRTM) elevation sources for this region.

eldron · June 07, 2021, 11:52:38

@ Sonny
I actually tried to download the N51E011.zip directly to my phone when i got back from the hike (from your DTM Germany 1" v1 folder), but it didn´t show up in the list. I think my phone had a problem to display the google drive content correctly, as it went from N50 straight to N54 in the list, with no N51 Files. I just opened the folder on the computer and all the files are there.
I´ll have a look at the files when i get home and download them on the computer this time instead of trying it on the phone.
Thanks a lot for your reply and for all your hard work to combine the elevation data from all the different sources and most of all for sharing your data with everyone. I´ll make sure to send a donation to you.

eldron · June 07, 2021, 15:06:15

I just tried Sonnys hgt file and it works like a charm - thanks a lot!
Interestingly enough Locus seems to ignore the hgt file information for the hillshades when using a locus map. With Sonnys hgt file i get the correct hillshades on the openandro map, but not on the locus map.
Is it correct, that the 1" files have a higher resolution than the 3" files (by factor 3), but in return are much larger in filesize (almost factor 10)?

Sonny · June 07, 2021, 15:19:54

Very strange the fact that LoMaps ignores the new elavation file if creating hillshades, maybe a caching problem?

About the files: Yes, 1" files (an elevation sample ca. each 25m) has a 3 times higher resolution than 3" files (an elevation sample ca. each 75m). And since there are 3x3 1"-samples in the same area of one 3"-sample the resulting filesizes are 9 times larger.

Menion · June 08, 2021, 14:37:24

Hi guys,
I would not call it a problem, but yes, it will most probably be because of caching. Please delete the Locus/cache/map/shader directory, it should help.

I've noticed @voldapet, he will look on it and probably fix it on the LoMaps side, thanks!

eldron · June 08, 2021, 17:05:36

@Menion
I renamed the shader cache folder and had another look at the map, but the hillshades where still wrong.
Afterwards I had another look at the newly created shader cache folder and the 3 subfolders where there, but empty. So by the looks of it no new cache files were created.
I´m just posting this in case it helps your bug hunt, for me the problem is solved, as I can use the openandro map for now and I´ll just wait for the Locus Map to be fixed too.
Once again I´m amazed by the level of support that this community and the developer delivers!