Combining Different SRTM Maps
choppinlt
Traveler
So I run into areas that cross different SRTM map sections. What are some good ways to combine SRTM map sections for CC3?
When I export entire SRTM map sections from FT3 to CC3 I get a bunch of "contour bunching" around some of the map edges. I think these are polygons closing during the conversion process. I tried adding a line and using the Trim function to clip them off, but that doesn't work. Thoughts, suggestions?
Best Answers
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WeathermanSweden
🖼️ 3 images Surveyor
Maybe @jslayton can answer this question in case there is a possibility to import more than one SRTM file into FT3 directly.
Just in case if there isn't a direct way, here is my approach...
There are surely plenty of programs out there that could shorten the process but most of them are quite expensive.
My goal was to use only programs that are free.
There is on the one hand WILBUR by Joe Slayton the creator of FT3. And he recommends on the other hand the pc software 3DEM on his website.
3DEM is a tiny but powerful tool that can combine e.g. SRTM's. The program has been abandoned and can be a little bit tricky to find - but a search on the internet still gives one or two places where you can download it.
The process in short:
Start 3DEM and choose SRTM data (second option). The dialog box opens when starting the program or can be found under File->Load Terrain Model.
Select all files that you wish to combine.
In 3DEM choose File->Save USGS ASCII DEM and save your data.
Start Wilbur and load the file: File->Open and choose USGS DEM Surface (*.dem)
The bridge between Fractal Terrains and Wilbur is the so called file format “.mdr”
There is a slight issue when exporting the file because when importing it to FT3 it will face up-side-down. To correct this we will flip the map in Wilbur before saving it.
Surface->Rotate->Flip Vertically
Now we can save the map: File->Save As MDR Surface (*.mdr) and save the file.
Start FT3 now. Choose File->New
Select Binary File
Press “Choose Elevation File”
You have to change the file type at the bottom to MDR Files (*.mdr) to see your file
Go to the right location on your drive where you saved your map and select it.
In the dialog box values will be filled in from the file.
Press ok and then proceed...
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WeathermanSweden
🖼️ 3 images Surveyor
My unzipped SRTM files have all the extension
.hgtso maybe the.bilfiles (that you have) are in another format?The files are about 2,75MB.
Here you can find 3" zipped SRTM's for almost the whole world. Just download a few, unpack them and try to load them in 3DEM.
Answers
Maybe @jslayton can answer this question in case there is a possibility to import more than one SRTM file into FT3 directly.
Just in case if there isn't a direct way, here is my approach...
There are surely plenty of programs out there that could shorten the process but most of them are quite expensive.
My goal was to use only programs that are free.
There is on the one hand WILBUR by Joe Slayton the creator of FT3. And he recommends on the other hand the pc software 3DEM on his website.
3DEM is a tiny but powerful tool that can combine e.g. SRTM's. The program has been abandoned and can be a little bit tricky to find - but a search on the internet still gives one or two places where you can download it.
The process in short:
Start 3DEM and choose SRTM data (second option). The dialog box opens when starting the program or can be found under File->Load Terrain Model.
Select all files that you wish to combine.
In 3DEM choose File->Save USGS ASCII DEM and save your data.
Start Wilbur and load the file: File->Open and choose USGS DEM Surface (*.dem)
The bridge between Fractal Terrains and Wilbur is the so called file format “.mdr”
There is a slight issue when exporting the file because when importing it to FT3 it will face up-side-down. To correct this we will flip the map in Wilbur before saving it.
Surface->Rotate->Flip Vertically
Now we can save the map: File->Save As MDR Surface (*.mdr) and save the file.
Start FT3 now. Choose File->New
Select Binary File
Press “Choose Elevation File”
You have to change the file type at the bottom to MDR Files (*.mdr) to see your file
Go to the right location on your drive where you saved your map and select it.
In the dialog box values will be filled in from the file.
Press ok and then proceed...
Wow, thank you @WeathermanSweden ! I havn't tried it yet, but I will definitely give it a shot. I found 3DEM so I am on my way. I REALLY appreciate this comprehensive answer. I will check back in and give an update....
OK I ran into an immediate issue. I downloaded 3DEM and Wilbur. I opened 3DEM and attempted to open 4 SRTM's, and it crashed. I rebooted to be safe and attempted to open 2 SRTM...one time it said I didn't have enough memory and the other time it crashed again. The memory issue should NOT be the case as my machine is less than a year old with 8GB of memory. I will mention that I did successfully open a single SRTM at a time, but that was it. Is there a setting or something I'm missing?
I suspect that 3DEM is a 32-bit piece of software. I haven't attempted to use it for many years now.
If you want a GUI for merging SRTM data, I would recommend GDAL (specifically, gdalmerge). If you're more of a GUI type, try QGIS. qgis - How to effectively merge SRTM 1 arc data? - Geographic Information Systems Stack Exchange purports to tell you how to merge multiple SRTM files into a single output, but I haven't tried it.
Be aware that FT3 is a 32-bit program and has a maximum size for a binary file of 1GB. Binary files must be uncompressed rasters, so a GeoTIFF probably won't work for you without some effort. I haven't merged multiple SRTM files for a long time now (I might have used one of the other datasets rather than raw SRTM, now that I think about it) and I don't recall what the best intermediary format for FT3 was.
@choppinlt What kind of SRTM's are you using? I remember that I was not able to load many 1" (about 25 Mb) and quite a lot of 3" (about 2,5 Mb). This seems to be a question of memory. My pc runs with 32GB of memory. This maybe explains why I could load some 1" SRTM files. Give it a try with 3" - are you able to load some more?
OK, @WeathermanSweden here is where my inexperience starts to show... after lots of struggles trying to figure out where to get the files and file types, here is where I am at. I got some .bil files from the USGS website. I opened each in FT3 just to test it out and I exported to cc3 just fine. BUT when I tried to open both files in 3DEM at the same time I got an incompatible Matrix Files message. I can open each one separately in 3DEM however. Shall I attempt to use the GDAL method mentioned above, or is there something else I can do (or havn't done)?
Thanks!
My unzipped SRTM files have all the extension
.hgtso maybe the.bilfiles (that you have) are in another format?The files are about 2,75MB.
Here you can find 3" zipped SRTM's for almost the whole world. Just download a few, unpack them and try to load them in 3DEM.
WOW, that works like a charm @WeathermanSweden !! This is really AWESOME! So the 3' hgt files worked just fine. Havn't thoroughly tested how many I can do yet, but I was able to get 4 SRTM together in CC3...Thank you so much!