Elevation on maps

[brucepos]

Hook - you've cost me three days of my life!

I got really interested in the idea of creating elevation maps directly rather than through the editor and wondered whether there was a way of using the free satellite elevation data that's avaliable. It turns out that you can do it, but it takes a bit of time. First of all, you can get the data from www.ambiotek.com/topoview/srtm41.kmz - this is an overlay for Google Earth, so you need this installed first.

Selecting the data centre nearest the location you want will produce a grid of satellite data sets - you can then pick and download the ones you need  - I had to download two because the area I wanted was in the middle of the sets.

The next bit is a bit awkward - I used a freeware programme called SciLab to do the donkey work. First you need to combine the datasets in a mosaic (if the region you want isn't entirely in a single set). Next you isolate the cells you need (the satellite data is divided into 0.00083333 degree elements (approximately 90m). Then it's necessary to resample the data to fit the 101x76 grid descibed by Hook - I used the linear interpolation function in SciLab for this. Finally, the data is exported to a binary file (the 'hgt' file described by Hook.)

I've generated a map for the Sacile battlefield - it was possible to add the river AFTER the height map was generated.

[TC237]

Great! 
I'm going to try it. 2 questions to start:
1) will it work with 30m elevation data?
2) can you write up some instructions? anything at all will help us to get started.

[brucepos]

I found the 90m data without too much trouble, but didn't find a 30m source (for google Earth), but it should work OK.

I'm writing a set of instructions at the moment.

[brucepos]

I've written (and tested) a set of instructions and put them in the 'Guides' section of the Histwar mods server (guggs.de/hwlg/)

Good luck - I'm off to play with the OOB editor now!

[spec10]

awesome guide, i just overflew it and it looks great. gonna try it out on the weekend if i find the time

[Tirailleur]

Wow brucepos,

this is fantastic work...thank you

[glaude1955]

Hi Brucepos,

Devil !, explained of this manner, all has the simple air...   
Congratulation and thank you for this small jewel that you offer to the creative amateurs. 

Yves

Diable !, expliqué de cette manière, tout a l'air simple... 
Félicitations et merci pour ce petit bijou que tu offres aux amateurs créatifs. 

[Bruguière]

Thanks a lot for your great job !!!!! 

[Broadsword]

Brucepos,
Thank you for some groundbreaking work (no pun intended) to discover this technique, and for making such a clear step-by-step guide to the process.

The guide was so encouraging that even I (not much of a math or programming geek) had a go at it. I actually got all the way through the steps in Scilab...until the part where you say to enter the first formula to resize everything:

-->x1=1:75/(nr-1):76;
               !--error 27
Division by zero...

Do you know what went wrong here? I cut and pasted the formula from the PDF exactly as written.

[brucepos]

Hi,

Thanks everybody for all the kind comments!

Broadsword - the problem I think you have is that 'nr', the number of rows in your data file is equal to 1. Did you check the datafile with the size operator 'size(mapdata)'? If it is 1, it suggests that something has gone wrong when you've been combining the data files.

Redo the Scilab part, and check the data sizes as you proceed. The individual satellite data files always seem to be 1200x1200, so your combined files should be multiples of this.

Hope this helps!

[brucepos]

Hi,

I've had a look over the PDF again and realised that you might have problems if you are cutting and pasting directly from the PDF. You can call the map data and combined data files anything you like - they are just variable names. I've been a bit free and easy with the names in the text, if you want to copy what I've done exactly, then use the code sections in the screen captures (apart from the 'CheekToCheek' one which shows data being joined side to side.)

[glaude1955]

Hi,
I don't get data marker to the screen.  
I took your example (venise) but no data marker.  
Has how I operated:  
I went on the site: Hole-filled SRTM 90m Digital Elevation Dated (V4.1)  
I clicked "here" to access the data  
Precisions of the site:  Welcome to TOPOVIEW : the Google Earth interface for the SRTM data (V4.1)    Once loaded into Google Earth, if you tick 'Elevation' under 'Temporary places', each of the grids that you see represents a 5 by 5 degree tile and contains a placemark which links to approx. 90m resolution digital elevation data  
I don't find the place to click " Elevation' under ' Temporary places "  
Where are Temporary places ?
What to make? Who help me ?
Thanks
Yves

[brucepos]

The attached google earth image shows what I've got on the screen, with the elevation checkbox clicked. To get the preview grid you need to click the 'data' pyramids near to your area of interest.

Hope this helps!

[glaude1955]

OK, I found them.
My google Earth was configured badly 
your first photo helped me 
Thanks
I continue toward the following step

Yves

[Broadsword]

Brucepos,

I followed all your steps, and it seemed to work OK in Scilab, but then when I opened my "Test" map in Histwar it was a mass of scattered little black dots.

Do you think you might be able to refine your manual a bit more, with more precise instructions and more explanations of the terms used? Also, could you show examples of how it works when you don't need to combine tiles and are using only one? I realize you've done a lot already by making this available, but it's a shame to have it not quite work when you've already put this much into it.

I felt as if I followed every step, yet it didn't work.

Thanks again,
Broadsword