Precise SRTM .hgt file handling

Markus Gpsmax shared this question 4 months ago
Answered

How is Locus Handling the .hgt Files ?

I mean, the SRTM format is same as BIL. Difference: just with defined pixel rows and clumns.

Is Locus able to handle a bigger .hgt file ? Do Locus calculate the pixel-spacing or just use one of the 2 normal possible ?

I want to use a much more detailled height model ! (Lidar Data with 50cm Spacing or 1 m)

Comments (13)

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Good day Markus,

if you have data prepared, best is to give it a try. I think it should work (and if not, create a bug report and attach one file for test). Only thing I'm little worried is fact, that app load necessary HGT files directly into memory for a lot faster work. 1m files will be probably really huge so there will be need for some automatic optimization and disabling this system. Anyway give it a try and you will see, I've personally never tried/used such huge HGT files.

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Ok, Thanks for fast Answering

I use GlobalMapper to export my Data to the .bil Format. (Motorola BigEndian Byte-Order) rename it to .hgt

Delete the corresponding File that Locus downloaded and replace it with my "new" one.

When I export my Data as .hgt -File (SRTM 1") i get it working but with the standard resolution. And it seems also to be very close to .bil format. (I am just able to export as .bil in custom Resolution)

I think i should keep the square Area of the Data so that Locus maybe is able to use it. (I don´t know how Locus parses the Data).

So I give it a try the next Days.

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I'm not sure if simple rename will work, you will see. I remember I worked with bil format some time ago, but it's direct internal support was removed few years ago.

App should anyway work with all HGT files, no matter how precise they are.

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It is working when i export as .bil file with same Resolution than 1 arc second. (so export as .bil and just rename works)

So it seems now that locus is just using one of the standard resolutions for srtm-files and can´t handle other resolutions.


Maybe if we say all files contain Data for 1 square arc second tiles. So we are able to calculate the point-density.

And locus load just a maximum count of opints to working memory (ram) ? to save memory.


My task is to use it in a mountain Rescue Team, and when we go to unknown terrain sometimes it helps to see in high detailled height model where are holes or steep rocks. or get back height values.


OK i can load a Hillshade-Map with high detailled Raster hillshade. but then i don´t have the right height data.

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Good day Markus,

I'm checking implementation of this feature and for me it should work, no matter how big are HGT files.

May you please share one file with me for test? Thank you.

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OK, yesterday i tried again. I exported as 0,1" grided Data. But Locus can´t work with it well.

If i Export as 1" grided Data then it works fine. (same method of Export as .bil, then rename to .hgt) I try to Attach a File with 0,5" Resolution. I hope the Size is not too big.

Are you sure Locus don´t just decide if Data is 1" or 3" ? Because in .hgt Files there is just a Grided Data, not the coordinates for each point. So Locus have to know how the Resolution of the Data is. But Locus also don´t work with Header Files... so... How do Locus find out the Resolution ?

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For me Locus is really the best mapping app on Android, so i hope my task is solveable. Now I try to generate 0.5" grided Data and attach. I don´t calculated but i think the Filesize is around 200MB for a 1 degree cell. I try it with my Region N47E009.

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Good day Markus,

our help desk most probably refuses upload of such huge file, so please use any Google Drive or similar service, thanks.

And app detects resolution of HGT file thanks to filesize. Size has to be always the same for the same resolutions.

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ok, i found out where the Mistake was..

My Data is in Meter accuracy, so exported them to grid resolutions for example: i tried 3m to 3m grid resolution.

But Locus Needs a binary dividable raster resolution of 1 arc Second. So possible is: 0.5 arc second grid spacing, 0.25" spacing, 0.125" spacing, 0.0625, ..., so ist not possible to make exactly 10m Resolution, but something close to.


So now it is working fine. thanks. I get really precise heights and also a Hillshade. (I see little rivers and also roads on Hillshade)

My next Task is to find a Software that generates better .bil data. (=.hgt data with Motorola Byte Order)Because Global-Mapper start produce Little stepps when use resolutions finer than 0.25 arc seconds as Export.

Or Maybe i let this data at a Resolution of 0.125" (close to 3m Resolution) and use a Map-Overlay (Multiplied) with Grayscale shaded Image of Hillshade. (I also use this on my Garmin Device).

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You found a problem with your generated files: perfect!

I'm glad it works for you now. If there will be something I may help with, feel free to ask.

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And yes... I didn't use the right Resolution.

After you told me, that Locus uses the File-Size to "calculate" the Resolution, it was all clear. I have to use square resolutions in divided parts of 1arc second. Thank you much.

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Hello

Now i have a question. When i plan a new Route manually (line of sight). And then look at the routes Height- Graph. Locus do not "interpolate" along the Route-Line, while viewing the graph ? Locus just usrs heights of the route points ?


Is it possible somehow to get a path profile ?


I think Garmin is doing it like: when you are in path-profile window, they "interactive" take tighter height points "below" the line of sight, while you zoom in.

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Hello Markus,

when you enable manual drawing that Locus should interpolate between the start/end points of the line for usage in Route planner. Usually, it should generate points every 100m. You see at the bottom chart only straight line? You may even slide up the bottom chart and then move with start/end point to see changes in the chart immediately! let me know if this works for you.

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