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How to download SRTM3 elevation data to locusmap Pro for USGS maps

blahdi shared this question ago

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I am a long time user of Locusmap Pro.

I have downloaded USGS map for washington state in USA, and would like to make sure I have the most accurate altitude data offline - useful for creating our own routes while alpine scrambling or snowshoeing.

Few questions:

1: I understand SRTM3 is more accurate than SRTM1 - How do I easily download SRTM3 files for the entire state?

2: I had previously used a app called DEM1 (which is no longer available on playstore) to download SRTM files, but I think those were SRTM1 files. Does that app still work and does it download SRTM3 files?

3: In addition to USGS Maps, I also have bought Lomaps for washington state, and I have downloaded elevation files for Lomaps from Locusstore. Is the elevation data that is downloaded with Lomaps SRTM1 or SRTM3? will that same SRTM elevation data be used with USGS maps?

here is a link to SRTM3 elevation data - https://dds.cr.usgs.gov/srtm/version2_1/SRTM3/North_America/

The same question

Replies (4)

blahdi ●

Here is a update:

about question 1 and 2: I have found a way to download SRTM3 1" files for US from viewfinderpanoramas. I am trying it out and will let u know if that succeeds. In other words, no need of answers for question 1 and 2.

about question 3: I have deleted all the old files in SRTM folder and will replace them with the downloaded SRTM3 1" files. I hope this clears all the elevation files downloaded along with LoMaps or with elevation fill. In other words, hold off on answering question 3.

Thanks all.

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blahdi ●

I downloaded the USA Washington State SRTM3 1" files (from this link http://rmw.recordist.com/gettile.php that is on viewfinderpanoramas), and then extracted the ZIP files and put the HGT files in SRTM directory.

I can see the slope shading when I am zoomed out, but slope shading disappears when I zoom in. When I zoom in, i get a notification says elevation data is missing. This was not happening with previous SRTM files that were downloaded using DEM1 app (long back).

Not sure why this is happening.

Pls advise.

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blahdi ●

I investigated this further.

Problem: Locusmaps is not recognizing the downloaded SRTM Files.

I deleted all the SRTM files, and got an error saying something like no elevation files. Then, I added few SRTM hgt files, and the error is gone, but there is NO shading in the area (latitude, longitude checked).

Pls advise. Thx!

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Petr Voldan ●

Hi,

briefly to you initial questions:

1. The difference between SRTM1 and SRTM3 is not in accuracy. The number 3 or 1 defines how detailed are the data, it's size of the grid. For SRTM3 it's 3'' and for SRTM1 it's 1 arc second.

2. Locus offers semi-automatic downloading of SRTM3 data

3. As source for SRTM data we use mentioned Viewfinderpanoramas and European data portal - please see https://docs.locusmap.eu/doku.php?id=manual:faq:how_to_add_map_shading#elevation_data_sources

Locus displays small icon in right corner of map view if elevation data are missing for area of interest. You can tap on it and download the data. Honestly I'm little bit lost in all steps you already did. So if you downloaded any external SRTM data - please copy the .hgt files into folder /Locus/data/srtm

To your latest issue - please check that data are really downloaded, shading is enabled and you're in correct location. Please send me:

- screenshot of map view without shading

- coordinates of the center of the map view (you can display coordinates when you tap on the top panel https://docs.locusmap.eu/doku.php?id=manual:user_guide:maps_mainscr_ctrl#information_field_2

- the .hgt file for this location

Thank you

Best regards

Petr

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blahdi ●

1. https://www.dropbox.com/s/olndbqxfebtww25/ScreenShot%20of%20files%20SRTM%20directory.png?dl=0

This directory contains

Locusmap screenshot with Mapshading enabled

Locusmap screenshot with Mapshading disabled

Screenshot of files in SRTM directory

2. https://www.dropbox.com/sh/fuyuv96cck537qo/AADi2iLUaPJGeq9E6rVSA2L9a?dl=0

This link contains all the HGT in SRTM directory that were extracted from zipfile for that location.

3. HGT zip file for location N42W120 was downloaded from http://rmw.recordist.com/gettile.php.

Responses to your other comments above:

1. Yes - technically its not accuracy of data, but I thought practically the elevation is inaccurate due to less granularity. [I am not an expert, but i have run into cases where the slope levels are not accurate and my guess was that it is because of less granularity of my *older* SRTM files.]

2. Glad to know Locusmap semi-automatic download is of SRTM3 data from viewfinderpanaroma for NorthAmerica. The viewfinderpanoroma site is a bit unclear on whether the data for NorthAmerica it has is 1" or 3". But, It points to rmw.recordist.com for 1" coverage and thats why I downloaded SRTM files from there.

Thank you.

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Petr Voldan ●

Hi,

thank you for the hgt files. I'm sorry but your SRTM data are not valid .hgt file.

Please see definition of hgt format - https://www2.jpl.nasa.gov/srtm/faq.html

Each data file covers a one-degree-of-latitude by one-degree-of-longitude block of Earth's surface. The first seven characters indicate the southwest corner of the block, with N, S, E, and W referring to north, south, east, and west. Thus, the "N34W119.hgt" file covers latitudes 34 to 35 North and longitudes 118-119 West (this file includes downtown Los Angeles, California).

Your hgt files are probably somehow tiled and do not cover 1x1 degree rectangle ( there are 80 files for Thus they aren't valid format Locus can't read them. You need to probably merge the files into one (I do not how :)) I would also suggest to check if the service where you downloaded these files. Maybe there is some option to download data in valid 1x1 degree format.

Thanks, Petr

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blahdi ●

really appreciated Petr. Your assessment seems accurate. Though, just fyi - I downloaded 3DEM application, and 3DEM did manage to render those files properly.

Next step: I will try to download directly from viewfinderpanaroma.org, and hope it downloads 1".

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blahdi ●

Petr - i downloaded the HGT files from viewfinderpanaroma.org and the elevation worked.

Thank you for your help!!

It might make elevation downloads simplier if Locusmaps could go through subdirectories of SRTM to find HGT files.. This way, users can simply unzip the files rather than unzip and then move all the files into a single directory.

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Petr Voldan ●

Thank you for info about 3DEM but the format of hgt files were really unusual. But I'm glad that you downloaded the file from ViewFinderPanoramas.

I'm sorry but I have to reject your idea. I think if anybody is able manually download the HGT files, unzip them, he can also move them to the proper folder. Sub-folders would also complicate managing of files, the would be problem with collisions (the files for the same area in different sub-folders).

Thank you for understanding

Best regards

Petr

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blahdi ●

I agree with the added complexity of duplicates, but moving is not as easy.

As a one time activity, i have to download 8-9 zip files to cover the 2 states, and then extract move and then delete all the empty directories.

Each state is not a unit - if in future i am traveling to another state i cannot simply download zip files for that state in a separate directory and then delete that directory after trip is over to save space.

Anyways, its not such a big problem now since i have now gone through the learning curve and figured out the details.

Thanks for your Help!

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