is it possible to create tin surface from DEM/SRTM file in bricscad?
Hi.
Is it possible to create a tin surface from DEM/SRTM in bricscad?
at the moment, I use QGIS to create contours from SRTM, then export those contours to DXF, save it as DWG file and crate a tin surface from those contours.
I'm looking for a way to eliminate the need for QGIS...
Thanks,
Ari.
Comments
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A DEM file is a GridSurface, not a TinSurface, so I seriously doubt you will ever see BricsCAD creating a TIN from it. Also beware that true DEM files are integer based so the elevations are rounded to the nearest meter. Not exactly quality!
Depending on your location, you may find some high quality government supplied Lidar, then you can use this free add-on to import that.
https://www.bricsys.com/applications/a/?lidartools-a1420-al2455
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@Terry Dotson
Hi and thanks for the reply.
I'm doing irrigation and water supply works - not municipal engineering, and that's set my accuracy determination.
First,
I'll try this free add-on you mentioned, Thanks!
second:
at the moment I use DEM from either https://earthexplorer.usgs.gov/ or from SRTM Downloader plugin in QGIS.
in your opinion - are those sources accurate?
thanks,
Ari.0 -
You will need to determine the accuracy (time limited here). All I know is the .DEM file format is integer based, that being the elevation values rounded to the nearest meter.
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@Terry Dotson
I've downloaded the Add-on.
the add-on required .LAS files and I get .GeoTiff files from usgs or qgis.
any advice on how to convert .Tiff files to .LAS files?
I've tried to google it but no good results...0 -
.TIF (Grid) Files are NOT Lidar (Point) Files. Look back, I never said the tool would help with your Grid Files. I said if you can obtain quality Lidar it would help.
However, since you have .TIF files instead of .DEM you shouldn't have to worry about rounding to the nearest meter.
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@Terry Dotson said:
.TIF (Grid) Files are NOT Lidar (Point) Files. Look back, I never said the tool would help with your Grid Files. I said if you can obtain quality Lidar it would help.However, since you have .TIF files instead of .DEM you shouldn't have to worry about rounding to the nearest meter.
@Terry Dotson
Thanks.
the add-on is good and when and if I will get .LAS files I'm Shure it will be good!
and about .tiff files - I will continue with QGIS...
and again - thanks for your help!
regards,
Ari.0 -
A late note - CloudCompare will very easily convert a downloaded .tif greyscale terrain height map (after trimming in QGIS) to any number of point cloud formats (.e52 seems most Bricscad-compatible), which POINTCLOUDATTACHes as nice wide-spaced (1x1m in my case) small-size point cloud in Bricscad, but annoyingly, not geolocated. It's relatively easy to MOVE from kms away (in Modelspace), ALIGN manually to the building model, and then readily produces a TIN.
However, I consider that Bricscad should be able to create both a point cloud, or at least a TIN, direct from a .tif, if only to preserve its geolocation data (if it's a Geotiff). The geolocation doesn't seem to survive the above conversions, or maybe it's just Bricscad's inadequate (?) dialog (not just crude command-line only, but lacking any GEOGRAPHICLOCATION-style data entry) - and the TIN>'create from file' dialog is even less useful.
Very interesting, my source offers both DSM (ground surface plus trees, houses etc) and DTM (bare ground surface only). As two TINs, they can be displayed superimposed simultaneously, switching between to compare. The ex-DTM TIN is ready to use
but the ex-DSM one makes trees look like the Rocky Mountains, just a useful diagram.
For me, these as part of my .dwg model (building model plus TIN) are for datasmith-export into Twinmotion but unfortunately so far TM refuses to import two TINs, just one, so am looking at converting the TINs to mesh before exporting.
Why then take the step of creating as TIN rather than direct to mesh? Because AFAIK a TIN is easier to correct and modify (with Bricscad tools) before converting to mesh (if I must) to send to TM.
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Problem gone away, both TINs now import to TM, display superimposed, no need to convert to mesh - don't know what …
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Re accuracy, just a comment we had access to tin models as part of our GIS CITY wide mapping from aerial flying, so we managed to compare to a road, manual field survey compared to the Tin data. We found that it was very reasonable around +- 20mm comparing points. But as we would work on roads that were around 1 in 400 slope a +20 mm was a huge pond on the road. So yes depends on what your doing how accurate you need. Don't fire your land surveyor just yet.
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Depending on where in the world you are, you might like to check the OpenTopography site.
This has the option of downloading topographical data in a variety of formats that can be utilised in BricsCAD. If your location is covered, the DEM file you're working with may well have been derived from this data.
Jason Bourhill
CAD Concepts Ltd
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I ought to check that source (again?). I found the UK Environment Agency/DEFRA data site by searching for 'better than Google Earth' or somesuch; its 1m resolution (LIDAR from aeroplane flyover) looks unbeatable, I'd think, compared to the (looks like) satellite data offered by OpenTopography for Europe? Half-metre is coming soon - already Netherlands have it.
Bricscad Support has just told me how to geolocate a point cloud - after POINTCLOUDATTACH - before making the TIN from that.
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Yes, for the UK, looks like you would go to the DEFRA Data Services survey portal to access LAZ data. For the USA and New Zealand (pre 2024), OpenTopography would be a good source. More recently Land Information New Zealand (LINZ) has added point cloud data to its LINZ Data Service portal.
A really useful feature is that this point cloud data is classified, meaning that you can filter between different point groups such as, ground, water, vegetation (low, medium and high), buildings and more. BricsCAD users (Windows only) that install the classifier libraries, can use the POINTCLOUDCLASSIFY to work with these classifications.
If your building a TIN surface from a point cloud this allows you to generate using just the points categorised to the ground.
Jason Bourhill
CAD Concepts Ltd
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