Sign in to follow this  
Guest jimkeir

Slartibartfast learning curve questions

Recommended Posts

Hello,Having grown comfortable with Ground2k and LWMViewer for enhancing lakes, I now want to learn Slarti, since Ground2k is a very labor-intensive tool when trying to enhance lakes for a larger region. However, I am struggling with a learning curve. I have read the Slarti manual a few times and have walked through the example, but I am stuck on the very first task involving the terrain data. I was successful in locating terrain data from the SRTM web site mentioned in the manual, but the reference lat/lon coordinates that I am supposed to put under the (Source) key in Slarti's INF file don't seem correct. Where do I get this value from the SRTM data file? From the name of the file? That doesn't seem to work, for when I use Slarti to produce a BGL file, then look at it in LWMViewer, the terrain mesh produced from that downloaded file is not properly aligned. The manual is a bit unclear about where the lat/lon value comes from, yet this is an important starting point to ensure the entire project is properly aligned with the sim's topography. Secondly, I am trying to locate the correct map off the LandSat web site linked in the help document that I can use for the lakes. What map do I download? I have to admit that I am using the example in the Slarti manual as a guide to starting with my project, which is to replace the lakes of the Adirondack Mountains of NY state (US).Incidently, has anyone else had problems with Ground2k's accuracy? I have been using the 16m resolution topo maps from MS's TerraServer as a background to creating lakes, but occasionally the lakes I create are off by as much as 1/2 mile in spots. I know this goes back to ensuring that I use correct lat/lon values for a northwest and southeast point, but it seems I am getting very accurate lan/lon coordinates from Terraserver. What would be causing this error.Thank you very much for any help you may have to offer. I really wanted to contribute the finished scenery to the sim community, but I want it to be of good quality. Right now, the G2k scenery files are pretty good, but I want them to be better and covering a larger area.

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

Hi Peter,Adirondack Mountains sounds like a neat project!First off, the TerraServer maps are not in the correct projection, which explains the offset. Most likely, they are in UTM projection whereas FS requires geographic lat/long. There's a thread here in the forum about freeware tools and methods to achieve a proper reprojection for TerraServer maps compiled with USAPhotoMaps.The SRTM mesh files come in 1x1 degree tiles (unless you download larger areas from the USGS or GLCF websites), and the reference point is the lower left corner. For example, the coordinates of the lower-left corner of tile N40W118 are 40N 118W. Thus, the inf file, which requires NW corner, would need to be set to lat 41, long 118. However, mesh files are compiled into the fixed LOD grid system of FS, which means that compiling single 1x1 degree tiles leads to gaps in between adjacent tiles (see http://www.fs-traveler.com/tips-d.shtml ). It's necessary to first develop a "master" mesh file for the entire project area and use that instead.However, since you're working in the US it's much better to NOT use the SRTM data but rather the seamless USGS NED 30-m data available here: http://seamless.usgs.gov/ They are of better quality and you can download large chunks with boundaries defined by yourself. I believe that Slarti can read the BIL format directly but you need to double-check the manual for that.Hope that helps.Cheers, Holger

Share this post


Link to post
Share on other sites

Hi.> Where do I get this value from the SRTM data fileThere's some information on this on p.25 of the manual. For SRTM, the information is all in the filename if you download the 1 degree tiles I used in the example. If you download from the USGS, the information will be separate depending on what you download. Make sure you change the file format from the default to 'TIFF'.You should be able to load BIL directly, it's basically just raw data. I can't remember what byte-order it's in so if "Type = ElevS16LSB" looks strange, try ElevS16MSB instead. Or the other way round :)For landsat, you should be able to more or less follow the example. On the GLCF interface, pick "ETM+" and/or "ETM+ Mosaics". Then just click on the map to zoom in to the area you need. When you get there, click on the 'Select' tool - an arrow with a + next to it - and pick the maps you want.Choose 'Preview and download'. You'll get a list of images, with previews of each. Try and pick the image(s) with the least amount of cloud because clouds need manual fixing. For each image, select 'Download' and take the *nn40.tif or *nn50.tif images, and the matching .met file. There's information on how to get the right values from this file on p24 of the manual.If you need anything else, just post here. Do let me know if there's anything that you think should be improved in the manual, too. Cheers,Jim

Share this post


Link to post
Share on other sites

Thank you both Jim and Holger. You have definitely given me some great information that has moved me past my initial problems.Jim, there was some great information in your manual that I simply overlooked. I think I initially filtered it in an attempt to get moving quickly.I'll post back if I encounter any other show-stoppers. Thank you both for taking the time to help.

Share this post


Link to post
Share on other sites

>If you need anything else, just post here. Do let me know if >there's anything that you think should be improved in the>manual, too. Jim, after spending the morning working with Slarti, it seems to me that a "known error messages and possible resolutions" section for your manual would be a good addition.As it is, I am stuck on the following error (output from STRIP) while trying to create a mesh-clinging watermap. I used Paintshop Pro to crop out a small subsection of a reprojected TIF file (as per Holger's recommended steps in the July 04 topic), then saved the file as a TIF with no alpha channels, but this is the error I am receiving:-------------- start output --------------------- Slartibartfast build Aug 16 2004 22:45:10 - Freeware*** Disabling ExpandMesh - no mesh loaded.*** Disabling NormalMesh - no mesh loaded.===== Reading config and data =====This program uses FreeImage, a free, open source image library supporting all common bitmap formats. See http://freeimage.sourceforge.net for detailsLatitude : N44* 14.7317'Longitude : W75* 7.1917'Width : 3940Height : 1768Cell Width : 0.000257Cell Height : 0.000257Raster Smooth : 2.500Vector Smooth : 6.000Peak memory usage will be around 33MbReal boundary area: Lat : 44.29687500 -> 43.59375000 (C130 -> C131) Long : -75.46875000 -> -74.06250000 (C223 -> C225)6 (3x2) cells to be processed.--> Loading water dataScaling "D:Application DataSlartiRacquetteSourceRacquette.bmp" Promoting image type 1 to 16-bit***Failed to promote image to 16-bit. Check that it has noalpha channel. e.g. in Photoshop, select 'Layer->Flatten Image'.This will be fixed soon!*** Failed to load image.The watermask only has a single value - ignoring it completely!*** Problem preparing watermap - erasing it.*** Failed to load source file(s).Now you can build the project using Racquette.bat .===== Statistics =====Points considered : 0Points used : 0VTP lines : 0LWM Polys : 0Raster Smoothing : 2.500Vector Smoothing : 6.000Total runtime : 0:00----------------- end STRIP output ------------------------Thank you for your time in helping me get started. I am really committed to learning this excellent tool, and I just need an occasional shove in the right direction. :)

Share this post


Link to post
Share on other sites

Whoops, that output is from my attempt at using the image in BMP format. I originally tried the TIF format, but received the same error message.

Share this post


Link to post
Share on other sites

Disregard this error; I figured it out. I also encountered another error having to do with too many values and no land found but I was able to figure that one out, too.As I stated before, the Slarti manual could use an errors and messages section, with common errors and possible solutions. That would be a big time saver. :)At 2:00 am local time, after working pretty much all day, I finally got a working scenery file containing lakes for a large portion of the Adirondacks using Slarti. With one quick position tweak, I was able to align the entire lake scenery almost perfectly with FSGenesis' 38m mesh.Over the next few days I need to clean up the Slarti-generated lakes (remove the ones that are too small, decide on a shoreline width, etc) but it looks like this will work.Great utility, Jim!

Share this post


Link to post
Share on other sites

Hi.Good to hear you got going, especially getting a usable scenery package so quickly once the initial problems were solved. An 'Errors and Fixes' section is a good idea. In fact, I did add an FAQ section the the website a while ago but it's not advertised anywhere so it's not surprising you didn't find it.The watermapping/masking process is definitely the most complex part of the whole thing. Having to back up and retry a few times is hardly unusual! Once you're set up, modifying the lakes is really pretty simple. You just load the bitmap/tiff/whatever into an editor and paint out the ones you don't want! The smallest ones can look a bit strange, especially with shorelines. Slarti will happily pick out details that are really too fine to be displayed well in the sim.Quick tip : one of the most persistent problems I had was dealing with inappropriate lakes. Quite often steep cliffs show up as very dark on the Landsat image, and these of course get taken as lakes. With a little practise you can usually spot these in Photoshop, but it's worth taking some time to check visually in the sim too. Again, you just paint them out of the mask and re-process.Have fun,Jim

Share this post


Link to post
Share on other sites

> Have fun,LOL! I am afraid it has moved past the fun stage and into "obsession world." One more quick question: Am I correct in my interpretation of your manual that the *only* way to guarantee fixed and correct lake elevations is to edit the BGS file (source file) afterwards?It seems that when using elevation mesh and a water mask, your manual states that there is a risk of water "step-downs" in larger lakes.Using the mesh-clinging option to create lakes is certainly easy, but I am concerned that the sim community will not accept a freeware enhancement that has lakes with uneven water (more common near the shoreline). Even FSGenesis' higher resolution mesh does not have completely flat areas where lakes are located, so mesh-clinging does result in lots of water level problems. Thank you for the tips and support.

Share this post


Link to post
Share on other sites

Hi Peter,I was very sceptical at first about Slarti's option to auto-determine lake elevation from the mesh and did the painful manual editing for quite a while. However, when I finally gave it a try it turned out that this feature works amazingly well. I used it for an extremely complex project with thousands of lakes and for most of the area (SE Alaska) I only had 60-m USGS elevation data. Because the lake polygons are often split into several LOD13 subsections I expected major steps. Yet, only about 20% of the larger lakes required hand-editing and most of those had steps of less than 5m, which were visible from the air only at very low sun angles.In short, if you're using USGS 30-m data as a base for your project, I highly recommend to let Slarti do the altitude determination. There seem to be a number of commercial US-wide lakes & rivers projects in the works and I'm very curious to see how they manage to deal with the elevation issue. Cheers, Holger

Share this post


Link to post
Share on other sites

>In short, if you're using USGS 30-m data as a base for your project, I highly recommend to let Slarti do the altitude>determination. Thanks for the suggestion. FOr the very short interim I am either hand-editing lake elevations for large lakes or using the mesh-clinging option. However, letting Slarti determine the elevation from underlying mesh is very high on my "must learn and use" list for this incredible scenery tool.>There seem to be a number of commercial US-wide lakes & rivers projects in the works and I'm very curious to see how they>manage to deal with the elevation issue. I imagine there are. I just hope I can release an acceptable package to the freeware section of Avsim well before one or more of these payware packages "hits the streets" (is released). Otherwise all of this work will be for nothing.

Share this post


Link to post
Share on other sites

Hi.> large lakes or using the mesh-clinging option. However, letting Slarti> determine the elevation from underlying mesh is very high on my "must> learn and use" list for this incredible scenery tool.Basically just load some mesh and set LWM mode 3! There are some gotchas you need to be aware of, though. The lake heights are set by the elevation of the points around the edge. If the terrain slopes *at all*, these will be different. Most of the time Slarti will pick this up, even on larger lakes, and pick a low value to use as the height of the entire lake. Sometimes though it can't work out what's a lake and what isn't. In that case, your lake will be assumed to be a river and won't have a flat surface. The only way to fix this is edit it yourself, after you're happy with everything else.Cheers,Jim

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this