blackart & global mapper

[Guest nanuk]

Hithese are great programs and really a lot of fun.I have had great success with 3arc SRTM. I can clean up the data and adjust it with Blackart. Then i can overlay DRG maps for G2k4.what interpolation settings are best for Blackart? Im using 65 and 65, but i read that interpolation can go into the THOUSANDS!One thing thats got me here is the inablity to clean up 1arc SRTM data in Blackart. I get some pretty weird results.i get stripes or bands in the finished product. (I had a pic in the print scrn key, but it dumped) like its smearing the data and then adds black lines spaced evenly across the map.can you clean 1 arc sec in Blackart?SRTMfill is giving less than adequate results, flat tops.dont have 43$ to spend on the other filler.any ideas?I know there is other data that doesnt require this step, but i like SRTM and would like to use the 1arc as well.lastly, anyone a Global Mapper expert? I have been creating overlays of my mesh with 24k DRGs. This really gives you a feel for how the mesh lines up and helps me in g2k. Other than that, what else can i do with this program relating to the sim?thanks for your input.

[Holger 0]

Hi Nanuk:I agree about Blackart; I'm just about done with a 3-arcsec SRTM mesh of Namibia and I used the batch mode to "clean up" all tiles. Since most of the holes were pretty small I used Laplacian only with 1000 iterations. For my other trials in more steep terrain, I found that 100 LSQR and 1000 Laplacian iterations provided the best results.One thing to remember is to always check John's site for updates; sometimes he posts several new versions per week ;-) Also, he does monitor this forum and responds to emails; anyone with specific questions or suggestions should contact him directly (and then, perhaps, report back to us here).Sorry, never tried interpolatiing 1-arcsec data. Also, I use a different commercial GIS (Idrisi) for most of my projects so I don't have much to offer regarding GM (other than it being the fastest translator between different projections I've seen!).Cheers, Holger

[Guest nanuk]

thanks holger,I will shoot John an email and see if its just me, or if 1arc is possible in blackart. I followed the same process as with 3arc and its not working.3arc will keep me happy till a solution comes up.@-@

[Guest nanuk]

here's some of my toying in GM.this overlay is on my srtm mesh. looks really nice in G2k. I can really carve out the shorelines with this background.http://forums.avsim.net/user_files/69845.jpgnot very good quality at 125kbshttp://forums.avsim.net/user_files/69846.jpgcolors and tranparency are all adjustable, plus just about everything else you can think of... lots of fun, i know im a geek. :-lolim also using your nice ketchikan backgrounds. nice addition to the library.you can never have enough data ;-)

[Guest nanuk]

back to 1arc and Blackartway at the bottom of the help file.10) BLACKART can open both 3 arc-second global SRTM files and 1 arc-second USA SRTM files. However, options for processing 1 arc-second files are limited at this point. The DTED0 merge option will not work. In addition, the extremely large internal arrays created by the 3601 by 3601 integer input file size will probably cause an out of memory error if you try to interpolate the entire file using LSQR iterations. You may be able to complete an interpolation if your computer has 1GB RAM but mine (with 256MB) crashed during an attempted interpolation. There are two possible work-arounds. The best is to use subset interpolation. Since this only processes a subset of the main array, even large input files will process relatively quickly. In the case of sea-level anomalies, you can use the clipping options without memory issues.In other cases, however, the missing data regions are two prevalent and too widely scattered for subset interpolation to be feasible. In this case it is possible to effect an interpolation using zero LSQR interpolations. Since the memory requirements for Laplacian interpolation are so compact, it is unlikely that memory will be a problem even for large 1-arc second SRTM files.----sounds like my answer, i havent tried it yet, but my problem was scrambled data, not crashing. I will give a try later.subset arrays when saved, clipped off 75% of the height field, bummer.nuk

[Guest nanuk]

blackarts v3.74 fixes the problem.but batch mode interpolation will not work for me yet with 1arc.nuk

[Holger 0]

Hi Nuk,nice images; that does look neat and helpful for G2K4 design.You might know this: when working with SRTM data you have to be aware of both errors of omission (voids) and errors of commission (incorrect spikes and dips, usually due to man-made structures). To check for those problems I find 3DEM - http://www.visualizationsoftware.com/3dem.html - extremely helpful. It has a neat 3D-view feature that allows for quickly spotting suspicious areas.Some of us also use 3DEM to take screenshots of a top-down colour-shaded image of the source data and then stitch several of those together to use as background images in Ground2K4. Obviously, this only works with data in lat/long format, such as the new Canadian CDED1 data. Don't have a screenshot handy but it works quite well for coastlines and rivers/streams.Cheers, Holger

[Guest nanuk]

Hi Holger,I passed a few emails back and forth with John Childs, and he fixed some errors with the 1arc batch interpolation and has posted a new version on his site.talk about service! amazing he isIm still playing with BA and GM and have had a lot of luck cleaning up srtm. I like how you can adjust the sea level to fix bumpy ocean.What i really like is when the topo is overlayed on your mesh, you can instantly see areas that are out of whack, and check for correct elevation and shorelines.thanks for the links.nuk

[Guest Giorgio]

Hi all.I've been using Blackart since a month, and i'm really amazed by the program, but the water despeckling option still gives me some headscratch.I'm trying to "clean" water bumps for my project (Cirenaica and Marmarica for CFS2), and I keep positive values very low (say, 0 in some hgts like harbors) to avoid draining away elevations in coasts, something that alas happens when you set such values higher. I've managed this way to have a clean sea in Blackart, but this does not correspond to the result: in TmfViewer (and in the sim) bumps are sadly still there. What to do? Is there any application that allows to frame given areas of the hgt, setting altitude values to zero inside your drawing, or is there any other solution in Blackart I've not yet discovered?Thanks for any help,Giorgio

[Guest nanuk]

im not sure how accurate this method is, but seems to work for me.IMAGE/ARRAY OPERATIONS/SET SEA LEVEL CLIPPING PARAMETERS-15 TO 15thenFIX SEA LEVEL ELEVATIONSit appears this zero's the sea level between the parameters idenitified.like i said it cleans the sea, but how accurate? dont know.maybe a better way?nuk

[Guest Giorgio]

Nanuk, this is just what I do but with different parameters (-30plus; 0). I'm keeping the positive value at 0 because higher numbers eat up the coastal mesh too, and considering that the scenery I'm doing is mostly made up with coastlines I'm trying to avoid any loss of data. Have you tested the "cleaned" meshes in a sim without default water flattens (like CFS2)? I don't know, it could depend on the parameters, but as I said the "clean" screen does not correspond with the visual result in the sim.Cheers,Giorgio

[Holger 0]

Hi Giorgio,just to clarify: are the elevations actually at zero after filtering in Blackart? Have you looked at the file in 3DEM or MicroDEM to check this?You can also do the levelling in MicroDEM, in two steps (both in the In/Out > Edit menu. First you use "specified Z value to missing" and then "set missing data to sea level". Obviously, you want to make sure first that you don't have any void (missing) areas elsewhere.Cheers, Holger

[Guest Giorgio]

No, they are obviously not: they just don't appear as fleckles on the Blackart program screen. For a beginner like me when the screen is black, well, it's fixed and let's go...Thanks for the tip on Microdem, it's really a mine of information, and I'm just playing with it. I'm using it now to discover the height average of SRTM bumps, so that I can fine-tune water despeckling in Blackart. Cheers, Giorgio