February 8, 2021 at 19:10 #41848
while in some other areas, they are less good than before. In this map, orange regions (radar source) have a bad precision and are smoothed in RGE Alti 5m.
It’s always a question if there is other, better source data in a region. In the region around Grenoble (as with almost all area of France) RGE Alti 5m is the best available right now. RGE Alti is not of constant quality all across France – but it’s always the best available within a region. So I’m quite sure that the source data I used before in this region was not as fine or/and it’s elevation not as accurate as it is now.
During comparision of 2 sources you don’t just have to look at the seeming fineness of its objects, you also have to check if this “seeming” fineness just occurs because of overlapped noise. In this case a smoothed DTM could result in more accurate contours than those with seeming finer details.
An example is DTM Nice which I used before RGE Alti 5m in the area of Nice and the nearby Alps: Its details look somewhat finer than the more smoothed RGE Alti in the Alps. But that’s just because of Noise. In the end after comparsion RGE Alti is better DEM regarding accurate elevation values and RGE captures steep mountain slopes more exact than the optical “seeming” finer DTM Nice.
And regarding the Locus-screenshots in the former post: I’m not sure if elevation files in Locus (did you manually install my 1″ files, not the 3″ which are provided by Locus?) as well as OAM map uses the latest DTM France files. Cause elevation in Locus says “1859m”, contour line “1890m” – this difference is to big. I think Christian wrote new France maps with the new DTMs are just about to be created the next days.February 8, 2021 at 22:40 #41852
The screenshot was done using your latest 1″ .hgt, and the february update of alps west. But in fact it seems the contour lines does not use these new hgt yet.: They have not changed since the previous one, at least at this location.
In the attached screenshot, the contour lines reflect your old 1″ hgt, with a hoodoo at 960m. With the new hgt, the hoodoo is much smaller (918m). This area is at the limit of the radar zone, and the river just below (le cheran) is outside, and more precise in the new hgt.
Attachments:February 9, 2021 at 11:09 #41860
You’re right, at the location of this hoodoo the old .hgt has been more accurate than the new one, the peak altitude differs about 30 m and the overall position seems to be a little bit better in the old version.
For the old version of this file, as well for many parts of the alps I used Viewfinderpanoramas’ 1″ alps-files. They’ve been excellent in the alps, cause its source data is NOT SRTM, but some (older) LiDAR data of IGN I guess – unfortunatatelly Viewfinderpanoramas doesn’t mention its sources. It’s my guess because they’re optical similar to the new IGN 5m files, and I don’t think there’s another organisation which provided LiDAR-Data of the whole French Alps years ago when the viewfinder-tiles have been built.
In general all across the N45E006-file the new IGN 5m data in most regions are finer, have less artefacts or are at least of the same quality as the former Viewfinder files. (compare images OLD 1 and NEW 1)
Since both possibly originate from IGN, I have no idea why in the region of your screenshot the newer IGN 5m is less precise. Of course there are also many locations where the new files represent peaks and ridges better then the old file. Compare images OLD 2 and NEW 2, the altitude difference where the arrow points is up to 100 m!
Since I have to decide what source to choose after comparison of the 2 source files, I’ve taken the new IGN 5m ones, cause almost everywhere they are better or at least of the same quality (although not at 100% of all locations) than the old ones.
Attachments:February 12, 2021 at 16:57 #41919
In general all across the N45E006-file the new IGN 5m data in most regions are finer, have less artefacts or are at least of the same quality as the former Viewfinder files
I think that all data that come from the radar source (shown in orange in rge-alti-sources) is lower quality than your previous .hgt files.
I computed the “smoothness” of old and new N45E006 tiles, then calculated the difference; negative values (blue) mean that the new file is “less smooth”, and positive (green to brown) means new file is smoother. Cyan means identical smoothness. Positive areas match the radar source. And in these areas, peaks altitude is wrong by more than 10 m.
I have still not found the geotiff that contains the source of RGE Alti data, it’s missing on the data downloaded from IGN; I wrote them to ask wher it can be found, it should allow to filter out those imprecise data.
Christian, can you confirm that the new altitude data has not yet been used to generate the contour lines in the February update (at least around 45°51′ N, 6°26′ E)?
Attachments:February 12, 2021 at 17:23 #41923
In general we can not say that just because a DTM is smoother than another on it’s also “better”, e.g representing elevations more accurate. I’ve already had source data which looked very smoothed not to say flattened. But its elevation accordance compared to a detailed LiDAR DTM for reference has been much better than those of a optical finer SRTM 1″ DTM fo example. So you finally just can judge the quality of two different DTM if you’ve got a better third reference DTMs in this regions for comparison.
I alredy wrote why I choose IGN 5m source in this region because right now it’s the best deal for most of the area. Sorry, if you want better data in this region you have to contact IGN if they could provide better data in your prefered region within their Open Data models.February 12, 2021 at 17:36 #41927
I created a new DTM of Iceland
Have fun!February 12, 2021 at 18:00 #41929
ChristianKKeymasterFebruary 12, 2021 at 18:03 #41931February 13, 2021 at 16:29 #41941
I redownloaded Alps West and the contour line are now OK. Maybe the previous download failed, or the new version of the map was not uploaded yet on the server. Many thanks! 😊
Have you considered adding some locus actions URL to install 1″ hgt that cover maps area? That’s certainly some work to package this, but currently one need to be a geek to install them from Sonny’s Gdrive.February 13, 2021 at 19:03 #41943
You are right, I support your idea to better integrate the download of the 1″ files within Locus. But I think this is not a feature a map provider has to care of – rather Locus itself. So it would be a good idea if you comment and suppport the following thread within Locus’ helpdesk:March 4, 2021 at 16:15 #42318
I created a new Version of Swiss DTMs, with great improvements in large parts of the country:
They are based on new high-quality OpenData sources of Swisstopo.
By the way: I created a Twitter account to post news and answer questions. If you want me to follow:
twitter.com/SonnyLidarDTMsMarch 17, 2021 at 22:37 #42632
I created new DTM of the whole of Germany. Not each federal state is offering OpenData elevation data yet. Please open the image “_Sources.png” in the download package to check the type of Sourcedata for each region.
Furthermore I created a new DTM of Slovakia, please check:April 9, 2021 at 16:04 #42888
There’s a new version (v2) of DTM Austria, my oldest DTM. Therefor I downloaded the latest LiDAR source data of Austria’s federal states.
Additionally I created 2 models with finer resolutions (10m and 0.5″). These fine gridded models will kept limited to Austria.
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