how to correct SRTM data?

[Guest Giorgio]

Hi all.I'm trying to finalize a project (mesh for Cirenaica and Marmarica) I was working on; I'm doing it with SRTM_to_BGL as Dos programs seem not to function properly (no possibility to insert any command) on my system.What I've discovered is that a tile of SRTM data contains a string of elevations, evenly spaced across a distance of about 100 Kms, each about 2500 meters high, that are not considered by Blackart as null-data areas (in fact they are not), and thus can not be safely interpolated.I do not know any way to cancel this data without spoiling the whole tile, or a big area of it: someone once wrote of the ability to "paint" wanted elevations in a paint program, but is it possible thereafter to convert the image file to hgt. format once again?Any other hint will be greatly appreciated,thanksGiorgio

[Guest sgreenwood]

Hi Giorgio,"I'm doing it with SRTM_to_BGL as Dos programs seem not to function properly (no possibility to insert any command) on my system."To open a window where you can execute DOS commands, click your Start button and select the Run menu item. The command you enter here depends on your version of Windows:for Win XP: cmd (opens a Command Prompt window)for Win 9x: command (opens an MS Dos Prompt window)Check Windows Help for more info on DOS commands and creating batch files to run them. Here is a link to a tip which allows you to open an XP Command Prompt window in a particular folder, using Windows Explorer:http://www.suodenjoki.dk/us/productions/ar...s/cmdprompt.htmSteve

[LuisFelizTirado 33]

Ciao Giorgio,You can use DEM2BSQ, available on John Childs' web site, I believe. This allows you to convert an hgt file to bsq, and then to a bitmap. Just paint over the wrong area with a color of another height, save the file, and convert back to bsq. The Microsoft Resample program will handle bsq files without any problem, but I seem to remember that you must modify your inf file to Type = ElevS16LSB.Just one thing: I have never been able to get Photoshop to recognize a converted bitmap. Perhaps there is some problem with DEM2BSQ, or more likely, with my computer. Anyway, I convert the bsq file to TGA, and it all seems to work out.There must be other ways to get a bitmap out of an hgt file.I assume that you are recreating the fascinating Italian campaign in the Cyrenaica and Tripolitana. Epic!Best regards.Luis

[Guest Giorgio]

Hi Steve and Luis. It seems that now I've finally managed to get a Dos program working, and that's already a good start. It will take some time before I learn the correct procedures to make a mesh with the MS resampler, but at least I begin to understand that there's more to it than simply using a do-it-all program. Luis, you are right! And the result (artifacts mended) is already very good...finally wadis look as they should. If you'd like to step back in time (and sim), a nice Lybia campaign is already available, made by Corrado La Posta. What I'm doing is just the mesh, some parts of coastline (Tobruk, Derna, bengasi etc.) and that's all. Pity that Ground2k has its obligations in terms of time - I would love to draw all coastlines and shorelines for Lybia, but my other wordly practices would be severely affected.., especially if you're working with DOI10 tiles. But I like it anyway.Ome more tip: as I'm working for CFS2, which resampler would you advice? FS2000 or FS2002? I say this because most recent meshes seem not to work properly in my aging sim (artifacts all over the place).Thanks for the help,GiorgioPS: Luis, I understand from your post that the passage from hgt to bmp has still its dark spots...

[Holger 0]

Hi all,"Just one thing: I have never been able to get Photoshop to recognize a converted bitmap. Perhaps there is some problem with DEM2BSQ, or more likely, with my computer. Anyway, I convert the bsq file to TGA, and it all seems to work out."The only method I've used for editing SRTM data is MicroDEM's height field editor but that's a VERY tedious and error-prone procedure. Anyway, to convert Photoshop greyscale bitmaps to 16-bit bsq format I've been using Jokin Bedialauneta Grises50 utility, available here: http://www.scenery.org/design_utilities_b.htmCheers, Holger

[LuisFelizTirado 33]

Hello Giorgio,I suppose that most of us are using the FS2000 version of Resample. From what I can remember, the later version did create some artefacts - was it not Dick Ludowise who did the tests on this? Perhaps he could remind us of the results.Best regards.Luis

[Guest luissa]

>You can use DEM2BSQ, available on John Childs' web site, I>believe. This allows you to convert an hgt file to bsq, and>then to a bitmap. Just paint over the wrong area with a color>of another height, save the file, and convert back to bsq. The>Microsoft Resample program will handle bsq files without any>problem, but I seem to remember that you must modify your inf>file to Type = ElevS16LSB.>>Just one thing: I have never been able to get Photoshop to>recognize a converted bitmap. Perhaps there is some problem>with DEM2BSQ, or more likely, with my computer. Anyway, I>convert the bsq file to TGA, and it all seems to work out.>>There must be other ways to get a bitmap out of an hgt file.Hello Luis,I think that John Childs programme is called MDEM2BSQ and that you may be referring to a tool that I wrote. I has been a surprise to know that PhotoShop could not open bitamps created by DEM2BSQ. Actually I only tested the bitmaps with "Windows Image and Fax Viewer", "PaintShopPro 5.0" (the one I use for image work), "ImageTool" (MS SDKs) and "Windows Paint". The bitmaps use the format of 4 bytes per pixel. So bitmaps converted from (BSQ/HGT) files will have more or less the double size of the HGT files as these use 16 bit per data point. Just after reading your post, I opened one of these converted bitmaps in PaintShopPro and just saved it. The saved file (bitmap of course) has about 3/4 of the size of the opened one. This is so because PaintShopPro uses 3 bytes per pixel. DEM2BSQ can read this "3/4 size bitmap" if I attempt to convert it back to BSQ.I read the bitmap format specification when I wrote DEMBSQ and I remember that the "4 byte per pixel" was a valid one. I wonder if PhotoShop (I have no access to it) has an option to accept this type of format.Kind Regards from (another) Luis :-)

[LuisFelizTirado 33]

Hola Luis,Thanks very much for your remarks. I believe that I got the program on John Childs' web site, but I may be wrong. There is no help file accompanying it, but it is signed PTSim, so it must be yours! Thanks for a very useful and intelligent utility. I have used it extensively and appreciate it very much.Perhaps somebody else with Photoshop could confirm or infirm whether a converted bitmap can be opened without error. I have not been able to do this, but this is not really a problem. I opened the bitmap with Irfan Skiljan's great image utility and saved it as TGA, which could then be opened in Photoshop.Best regards.Luis (the other one)