Author Topic: Hill shading and HGT downloads  (Read 3063 times)

Offline michaelbechtold

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Hill shading and HGT downloads
« on: March 15, 2016, 21:14:54 »
Tried Hill shading for areas for which I do not yet have the HGTs on my SD.
Funny effect: the HGT covers more than shading is displaying. But the dynamic elevation does recognize and display the value. I attached a typical situation.

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Offline menion

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Re: Hill shading and HGT downloads
« Reply #1 on: March 15, 2016, 21:39:57 »
Map tile is shaded only for tiles, where is 100% cover of elevation over HGT. When few pixels don't have elevation (missing HGT file), whole tile is not shaded.
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Offline michaelbechtold

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Re: Hill shading and HGT downloads
« Reply #2 on: March 15, 2016, 22:00:21 »
Arghhh, so tiles and HGT are not aligned - did not know / anticipate that.
But why are you so strict ? Why not just shade what you can ? Anyway, no big deal, now that I understand why/how.
 

Offline menion

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Re: Hill shading and HGT downloads
« Reply #3 on: March 15, 2016, 22:17:48 »
Why? Mainly a simplicity of algorithm where you do not have to care if data are on certain pixel or not. I just quickly test if they are everywhere (over whole tile) and if not, tile is skipped. Fast and effective.
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Offline michaelbechtold

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Re: Hill shading and HGT downloads
« Reply #4 on: March 19, 2016, 12:30:49 »
Just d ownloaded latest beta and tested hill shading on two devices. One has 3" HGTs,  the other has 1" HGTs. Both show missing tiles in the middle of downloaded areas. No pattern I can see, random effect,  but reproducible as far as I perceive.

edit
Zooming in can show tiles from lower zoom in some places.
« Last Edit: March 19, 2016, 13:06:55 by gynta »
 

Offline menion

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Re: Hill shading and HGT downloads
« Reply #5 on: March 19, 2016, 13:25:48 »
Good day Michael, this is known issue to me. It do not happen randomly, but only on places, where is absolutely no information on below vector map. So in case, vector map has nothing to draw on tile (no line, no point), shading is also not able to draw. Quite complicated to solve now, though I'm aware of it.
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Offline gynta

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Re: Hill shading and HGT downloads
« Reply #6 on: March 20, 2016, 23:20:38 »
btw.

What's the big(?) difference between 3" and 1" files:

3": 1,75MB
1": 24,7MB - whole Alps 2,5 GB (roughly)

Compare...

...slope: http://www.oldboys.at/comp1/
plausible view?

...hillshading: http://www.oldboys.at/comp2/

Offline michaelbechtold

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Re: Hill shading and HGT downloads
« Reply #7 on: March 21, 2016, 08:04:06 »
btw.

What's the big(?) difference between 3" and 1" files:

3": 1,75MB
1": 24,7MB - whole Alps 2,5 GB (roughly)

Compare...

...slope: http://www.oldboys.at/comp1/
plausible view?

...hillshading: http://www.oldboys.at/comp2/
Ich habe letztens etwas gespielt und es gab Orte wo die beiden massivst unterschiedlich waren.
Everybody needs to decide about cost /  benefit of pot. 3 times more details versus 10 times bigger files.
My finding below does not apply to 1 versus 3", it is a general issue, as Menion confirmed.
Not sure though why there is no map tile painting as without shading and only then a systematic nested loop (x, y) for the shading. A second loop should practically have no overhead compared to the operation in its core, the shading itself ....
Cheers from Casa
Michael

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Offline szebenyib

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Re: Hill shading and HGT downloads
« Reply #8 on: April 11, 2016, 16:47:18 »
Hi menion!

Is it somehow possible to select an area and download hgt data for it? Like it is possible to do with maps.

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Offline menion

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Re: Hill shading and HGT downloads
« Reply #9 on: April 11, 2016, 17:05:27 »
Ideas, wishes, problems
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Offline michaelbechtold

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Re: Hill shading and HGT downloads
« Reply #10 on: April 11, 2016, 19:13:52 »
Hello,
no it is not.

Idea already exists here: http://help.locusmap.eu/topic/more-comfortable-srtm-download-for-hill-shading
This link has some work around that I built.

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Offline szebenyib

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Re: Hill shading and HGT downloads
« Reply #11 on: April 15, 2016, 10:11:44 »
Voted for it, thanks!

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