Author Topic: SRTM- no attitude in some points  (Read 3798 times)

Offline locuscycling

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SRTM- no attitude in some points
« on: March 14, 2013, 19:42:01 »
What is the best  - ,,landform'' for Locus.

I am using SRTM files with extension hgt ( this same as for Ozi Explorer). I don't know- my problem is becouse  :
a),, SRTM '' are not full ???
b),, It is a problem with Locus ???

What i mean. It is going about ,,DYNAMICAL ATTITUDE''. All screens are from Pic du Midi di Biggore region-Pyrenees. ( but in Alps i saw the same problem)

When i tap a screen normally i see attitude like this or


But sometimes i see ,,0'' like this
The text at the botton (in polish) means ,, For one point it is impossible to corectly calculate attiude''

Normally we doesn't care about this but... when we want to calculate ( or create) route and see Chart, descent and ascent of created route  it can be a little problem.

See this Chart ( with holes) of calculated ( by internet) route
and what's more INFORMATION details see

Total ascent 15000 m.....???? It is a long climb (This is climb to Midi di Biggore  ( Col de Tourmalet is on the road)),  but of course ascent will be less then 2000m not 15000 it is impossible.
The additional  13000m is becouse of points of the road where Locus ( or SRTM) could not calculate attitude ( 53 points)

( For 53 points it was impossible to corectly calculate attitude)

I tried to see the same map in TwoNav with Europa DEM and in this same part of the map i always get ,,normal'' attitude ( no 0) like this



I dont know where is the problem?


.
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Offline tommi

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Re: SRTM- no attitude in some points
« Reply #1 on: March 14, 2013, 21:03:33 »
This problem also occurs in other regions, the SRTM data isn't perfect
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Offline locuscycling

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Re: SRTM- no attitude in some points
« Reply #2 on: March 14, 2013, 21:18:50 »
Yes I know- I also  saw many ,,holes'' in other regions - generally in high mountains  ( where there are a lot of ''verticall walls'')

You think Tommy it is a problem with SRTM ? not with Locus?

 Maybe converting ( i mean easilly) better DEM for ex. from  TwoNav or another source  is possible?
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Offline menion

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Re: SRTM- no attitude in some points
« Reply #3 on: March 14, 2013, 21:36:03 »
what SRTM files are you using? Downloaded by locus? Some new (from this year) or older?

Also if you provide some track with these holes, I may check places and also check SRTM files. Anyway files were all scanned! (for whole world) and should be optimized and without holes!! So you're probably using some older files or there is any issue in Locus. Track for test helps
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Offline tommi

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Re: SRTM- no attitude in some points
« Reply #4 on: March 14, 2013, 21:42:12 »
Quote from: "menion"
what SRTM files are you using? Downloaded by locus? Some new (from this year) or older?

Also if you provide some track with these holes, I may check places and also check SRTM files. Anyway files were all scanned! (for whole world) and should be optimized and without holes!! So you're probably using some older files or there is any issue in Locus. Track for test helps
I didn't update my few SRTM files downloaded via Locus for a long time. Maybe that is the reason for what I observed several times. I'll delete them and fetch fresh ones, was not aware that there was improvement.
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Offline locuscycling

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Re: SRTM- no attitude in some points
« Reply #5 on: March 14, 2013, 21:53:13 »
I downloaded SRTM from this adress:
http://http://dds.cr.usgs.gov/srtm/version2_1/SRTM3/Eurasia/

My training track -see enclose.
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Offline gynta

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Re: SRTM- no attitude in some points
« Reply #6 on: March 14, 2013, 21:54:16 »
use Locus better SRTM files than this one:
http://www.viewfinderpanoramas.org/dem3.html#alps

(talkingh about the 1" Resolution files)

sorry for hijacking this thread :roll:
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Offline locuscycling

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Re: SRTM- no attitude in some points
« Reply #7 on: March 14, 2013, 23:20:27 »
Thanks you all very much.

I downloaded new SRTM and it it Ok.

Now i have on this same track  correct attitude  data without ,, holes'' .

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Offline menion

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Re: SRTM- no attitude in some points
« Reply #8 on: March 15, 2013, 06:19:11 »
update of hgt files was somewhere in December if I remember correctly. We needed whole world for vector maps, so on locus server is for download complete all possible hgt files, all are highly optimized, some of them merged from several sources and non should have any hole!. Seems you confirmed this, perfect ;).

And to gynta note, Locus offer for download "only" 3' data, so if you want higher resolution, you need to download them somewhere on your own. Difference in precision was shortly tested on our side and because difference was quite small, we decided to use 3' data due to very high difference in size. Anyway it's up to you, Locus should be able to handle both
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Offline tramp20

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Re: SRTM- no attitude in some points
« Reply #9 on: March 15, 2013, 07:41:40 »
Quote from: "menion"
what SRTM files are you using? Downloaded by locus? Some new (from this year) or older?



I searched but I did not find the right url :-(

My .hgt files are from 03.2012.
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Offline menion

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Re: SRTM- no attitude in some points
« Reply #10 on: March 15, 2013, 10:28:29 »
ok, but this means your files are downloaded by your own, not from Locus right? Then I suggest to downloaded them from locus and you'll see.

Anyway it's simple:
- hgt files from other then locus sources, may contain holes, may have problems
- hgt by locus should not have any holes and missing data! If so, send me coordinates and I'll check it
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Offline tramp20

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Re: SRTM- no attitude in some points
« Reply #11 on: March 15, 2013, 10:59:55 »
Quote from: "menion"
ok, but this means your files are downloaded by your own, not from Locus right? Then I suggest to downloaded them from locus and you'll see.


I would like download your hgt files but how and where?
I tried and tried...
Perhaps I am on the free test version and I am not allowed to download from store?
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Offline menion

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Re: SRTM- no attitude in some points
« Reply #12 on: March 15, 2013, 11:32:06 »
they should be available in test version also. just try fill altitude to any track or points
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Offline gynta

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Re: SRTM- no attitude in some points
« Reply #13 on: March 15, 2013, 11:43:35 »
i think he want a url...

edit
with google we will find a lot of sources
..but where are the latest  and/or the most accurate?
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Offline tramp20

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Re: SRTM- no attitude in some points
« Reply #14 on: March 15, 2013, 11:46:25 »
Quote from: "gynta"
i think he want a url...
Yes, of course.
I already loaded the hgt files from your link above but menion prefers his own :-)
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