How do you merge SRTM and GTOPO30? Are you using MICROdem?Also... what about things like lakes and so on. In some northern parts of Canada, they seem to be using their own altitude, which in turn makes them look like big buckets of water in the middle of nowhere. Any ideas?

Howdy:yes, I believe that the best way for merging is to use MicroDEM; you'll have to resample the GTOPO30 DEM to the same resolution as the SRTM file prior to merging.as to the buckets of water: I mentioned that problem in the last paragraph of my previous post here. When MS matched their water linework and polygons to the default mesh they seem to have lowered (or raised) the lakes to the surface, regardless of the true elevation. Along comes a new add-on mesh with correct terrain elevation, only to end up with lots of "holes" and "mesas". I believe that Gilles Gauthier's fixes for Quebec and the Maritimes are currently the most elegant method whereas my flatten switches were the brute-force approach. Either method requires a lot of tedious work and good topographic maps.The ideal solution would be to acquire hydrographic vector and polygon data that matches both in resolution and quality the SRTM meshes and use those to compile your very own set of hydrography .bgl files.Cheers, Holger

Hi David,Yes, I do use Microdem. There are several steps involved and the results are far from perfect, especially along the edges. But I've encountered areas of missing data almost 1-degree square, and this is better than interpolation for such large areas. I still go in and manually fix any small remaining problems if I see them.If Matthew can develop a way to resample and merge the GTOPO30 or Globe data and smooth the transitions between the data sets, it would provide much better data to work with. :-)1) extract a small subset of the GTOPO30 data for the area2) load the subset and save as a DTED file, resampling to 3 arcsec3) merge the data, loading the DTED file(s) first, then the SRTM data4) you may have to take a subset of the merged data, if your DTED data extends beyond the boundaries of the SRTM data.I turn off auto-filling and do it after the merge, but this does not work perfectly, and I still have to set missing values to sea level. I plan to try leaving it turned on for my next test.Microdem Options:* Import/Export - Auto-fill holes on DEM merge (I'm using 100 as max gap to fill, but no sound basis for this value)* Views - Missing values set to sea levelYou may find Globe data easier to work with; it is available in one-degree files. I've recently downloaded the Globe data and nasa jpegs (2 files, about 250MB each) from:http://globe.unibuc.ro/mapdata_zipped/These also work well with the Blue Marble option in Microdem. This feature is not really useful for our purposes, but is fun to experiment with!The lakes are a problem. The elevations can be altered with flatten bgls but it is tedious work when done on a large scale. Holger created "tons of flatten switches" for his BC mesh. My flatten utility creates flatten bgls fairly easily:www.fs-traveler.com/flatten.htmlSteve

Hi all.There is one other method for handling lakes... although I do hesitate to suggest it.The default LWM bgls could be replaced with CFS2 style LWM bgls. This would be accomplished by decompiling the default LWM BGLs with and then using using Edgar Knobloch's [link:library.avsim.net/esearch.php?DLID=&Name=&FileName=cfs2conv.zip&Author=knobloch&CatID=Root]CFS2Conv, then recompiling as CFS2 LWMs.CFS2 LWMs have no elevation. They cling to the mesh. If the mesh is sufficiently detailed, there is little need to use flattening.This would cause problems for uninstalling the scenery, as the defaults would have to be reinstalled.This might have to wait for a 'corrected' shuttle DEM set, as waves, swells, and other things are now present in the water.Dick

Thanks for that... Ill address those bugs in the next versionMatthew.

Hi all,The Martin Wright's new updated of FSTerrain 2002 has integral support for the new SRTM HGT data and GTOPO30 DEM data can be merged to help correct SRTM errors.http://www.mnwright.btinternet.co.uk/index.htm

Nice!Actually I tried it before i started writing the SRTM_3ARCSEC_TO_BGL utility.My goal with SRTM_3ARCSEC_TO_BGL is to make it as simple as possible... just run it and nothing else to do or configure!I might add a simple GUI to make it more accessible to people who are not comfortable with the DOS prompt and batch files.Really I just want it to be a "Mesh for Dummies" type of program. I think i will add in ability to download SRTM from Net, and ability to install BGLs into FS2002/2004... all from a simple GUI "Wizard". Then there will be no need to work with DOS prompt at all.BTW - Merging GTOP30 with to fix holes is a great idea. Must try to put it in soon.Matthew.

Hello Matthewyour work is so incredible do get fast results. this way big meshes are possible on an easy way.Only be careful when you want to divide the mesh in small bgl's because your programm reads the mesh not completly but restrict to LOD9 cell's so there will be always blank strips around. I solve this by generating bgl's out of 16 *.hgt files (4 x 4) where the neighbour - one's overlap one degree width. hmm... this creates double redudant data, but the work is fine!i run your program inside a batch which select certain hgt's out of a folder so it looks like this:del *.hgtdel SRTM_3ARCSEC_TO_BGL.batdel SRTM_3ARCSEC.infcopy ..sourceperu9*.*SRTM_3ARCSEC_TO_BGL.execall SRTM_3ARCSEC_TO_BGL.batrename SRTM_3ARCSEC.bgl qowimesh_9.bgldel *.hgtdel SRTM_3ARCSEC_TO_BGL.batdel SRTM_3ARCSEC.infcopy ..sourceperu10*.*SRTM_3ARCSEC_TO_BGL.execall SRTM_3ARCSEC_TO_BGL.batrename SRTM_3ARCSEC.bgl qowimesh_10.bgl...so i just seat back and let the computer work!what would be interesting is:- implementing whether to get error-hole data out of GTOPO30 (must be in same directory... but what format?) or to interpolate data - as it does now.- while creating the *.bat adding an option to create either LOD8 or LOD9 files, which would automatically create the accurate *.inf.now, big work must be done by reflatten polygon -rivers and lakes, deleting default rivers and streets, and puting newones!Thanks again Matthew for your work!SaludosFrancis