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Guest sgreenwood

What LOD do I get from 1:100 000 Topo

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Hi all,Happy to part of the comunity. :)I have just made my first Mesh scenery for my area (Svalbard). The mesh is made out from a 1:100 000 topo map, which is is scanned at 150DPI (16.9m pr pixel). Measuered in the MS LOD this would be about 10 or 11, but this would not be totaly true. On the scanned 1:100 000 map there is 50m between each hight line, and after Interpolating it's 0.1m. I know it's wrong to use the LOD10, but I'm not able to figure out the correct LOD. The LOD tables only reffere to LOD values as a result of distance in the xy(Lon/Lat) axis, not the z(elevation).Can sombody tell me exactly what LOD to use?At the moment I have found that LOD8 is best, this by comparing results for the different LOD.Note: The 1:100 000 TOPO is the best resolution for topo maps at Svalbard, so it's doesn't get better than this.Have fun,Finn-Aage

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Hi Finn-Aage,I haven't made mesh this way, but maybe I can help."but I'm not able to figure out the correct LOD. The LOD tables only reffere to LOD values as a result of distance in the xy(Lon/Lat) axis, not the z(elevation). Can sombody tell me exactly what LOD to use?"LOD specifies the horizontal spacing of the data points in the BGL, so I would suggest LOD10, since your source data is 16.9m per pixel. LOD11 matches better, but requires editing your cfg file to see it, and I'm not sure if it will look better. The default vertical scale (z axis) is in meters, although you can change this if your elevation values are not in meters, but this is rarely necessary. "there is 50m between each hight line, and after Interpolating it's 0.1m." What do you mean by "interpolating"? I assume you are loading it into a "paint" type program and viewing the elevations as a gray scale. Were you able to adjust the elevations of the individual points between contour lines to provide a smooth gradient? If the real vertical interval between elevations is 50m, then the lower lOD 8 value may be better since it will help hide the steep steps between elevation levels.Steve

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Hi Steve,and thanks for trying.I guess I should have been more precice in my question, and what I have done.The source I started with is a 1:100 000 paper map. This map has 50m vertical spacing (interval between each contour line).The horizontal spacing is depending on how I scan the map. I hav used 150DPI (16.9m), but I could as well have used 300DPI (8.45m) or 600DPI (4.225m). So deciding the LOD value from the horizontal spacing would not be 100% correct.My question should have been frased like this: "Is it posible to decide the LOD value out from my 50m vertical spacing?"My "Interpolating" is as you guessed, but done differently. My Contour lines are converted to Vectors and I then use John Childs program BlackArt for interpolation. The output is a gray scale image with, and when converted to USGSASCII DEM the vertical resolution is 1m (not 0.1m as I wrote earlier). This process is done to get ridd off the steep steps between elevation levels.Any suggestions?Regards,Finn-Aage

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Hi,"My "Interpolating" is as you guessed, but done differently. My Contour lines are converted to Vectors and I then use John Childs program BlackArt for interpolation. The output is a gray scale image with, and when converted to USGSASCII DEM the vertical resolution is 1m (not 0.1m as I wrote earlier). This process is done to get ridd off the steep steps between elevation levels."Very clever. :)"The horizontal spacing is depending on how I scan the map. I hav used 150DPI (16.9m), but I could as well have used 300DPI (8.45m) or 600DPI (4.225m)."So you increase the accuracy of the vector locations by increasing your scanning DPI. I am not familiar with John's program, but the resolution of the DEM he creates is the resolution you should be concerned with when creating the inf file, not your scanned resolution, unless they happen to be the same. And it is this resolution that we try to match to that of the LOD used. If you are providing the data for BlackArt in vector format there is probably no resolution information included. A quick check of his site and app Help file offered no insights about his output resolution. Does his app give you row/column information for the DEM? You may need to use these values and the boundary coordinates of the source data to calculate the spacing, much like we calculate the CellX and CellY dimensions.Steve

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