Discussion: blast2dem

Can you explain this step a little bit?

Is the end result an image file? If so, what format?

I don't seem to have blast2dem in my LAStools program. Is it an extension?

A few of the maps I've made recently were used with older LIDAR (2000), but King County just got fresh LIDAR from 2017, and besides contours and karttapullatin, I'd like to see some images where it might be possible to see exactly where the trails go in the woods.

Thanks!

For reference, here is the bach I usually hit when I have small area and one laz file. I tend to merge/crop with laszip (I use -merged option), never used lasclip.

C:\LAStools\bin\las2las -i tile.laz -o slope.laz -keep_class 2
C:\LAStools\bin\las2dem -i slope.laz -opng -slope -step 0.5 -gray -invert_ramp -set_min_max 0 45

C:\LAStools\bin\las2las -i tile.laz -o forest.laz -keep_return 1
C:\LAStools\bin\las2dem -i forest.laz -opng -slope -step 0.5 -gray -invert_ramp -set_min_max 0 75

C:\LAStools\bin\lasheight -i tile.laz -olaz -odix h -replace_z
C:\LAStools\bin\lasgrid -i tileh.laz -step 2 -elevation -highest -false -set_min_max 0 40 -opng

pullauta tile.laz
copy temp\out2.dxf contours.dxf /Y
copy temp\dotknolls.dxf dotknolls.dxf /Y
pullauta xyz2contours 0.625 xyz2.xyz null out.dxf
pullauta smoothjoin
copy temp\out2.dxf contours625.dxf /Y

As a result I'll have 0.625 m contours for field checking and some images. I tend to use first return instead of last like you do, I think I used to see fences or something better with that. May be data density issue.

I think there are different options for the image format. I save it as a .png with a .pgw for georeferencing.

Blast2dem came with LASTools. I guess you can probably get just blast2dem at: https://rapidlasso.com/lastools/

I can often get the trails by doing a slope image of just the ground points. Sometimes I do two slope images, one with the normal settings and another with the "z" exaggerated.

Another useful lidar tools is "RVT" https://iaps.zrc-sazu.si/en/rvt#v

I haven't used RVT for Slough Creek, but I used it for one of the areas at Clinton and was able to see a lot of the trails in the "sky view factor" image.

I tend to use first return instead of last like you do, I think I used to see fences or something better with that. May be data density issue.

I'll have to take a look and see what I get from the first returns.

Oh, looks like I do have it; it's just not listed in the GUI for LAStools (there's a las2dem there, though). Apparently it's a standalone. Now that I have it, I'll try playing around a little.

Ok, I'm finally playing around with blast2dem.

I have a point cloud LAZ file, but every output I get from blast2dem shows the top surface hillshade. How do I go about getting the last returns?

I tried using a filter of "last_only", but that ended up giving me the same result.

Here is the command that I use for one of the blast2dem images I like to use for mapping:

blast2dem -i "C:\Users\Michael\Documents\OMaps\TinyMaps\DanforthChapel\KPmap\Danforth1.laz" -last_only -slope -gray -odir "C:\Users\Michael\Documents\OMaps\TinyMaps\DanforthChapel\KPmap" -o "AllLastSlope1.png"

The result:

Slope image with all classifications but only last returns. The rectangular building on the west edge of the image is Fraser Hall on the KU campus. pic.twitter.com/b8lzR7PTp3

— okansas (@okansas) October 17, 2018

Hmmm... thanks! I'll try playing around a bit more. I'm working on some basemaps for some forested areas that have LIDAR, but I really haven't done a lot with KP or with LAStools in my other projects, where I just care about getting basic contours.

Some other questions... I have OOM, KP, and LAStools. When creating a basemap, I'd ideally like to have georeferenced data from OSM, photos, and contours.

I know how to get georeferenced OSM data into OOM. Some photos automagically become georeferenced in OOM as a template, but others aren't. Is there's a good place to get georeferenced photos now? USGS somewhere? I don't really care about quality because once I have something in there, I can add other photos and georeference them manually with the already-georeferenced ones.

And what about KP outputs? Is any of that stuff georeferenced well? I just tried to import one of the PNG files and it didn't work, and when I try to import KP DXF files, they show up who knows where, so I just bring them "at view center" and manually adjust them to fit. (I've had to manually adjust LIDAR contours for all of the maps I've made to date. It's doable, but if I'm going to be making a bunch of basemaps, I'd actually like to learn how to do this right. :-)

KP outputs - the various png files and the dxf files with contours - are all georeferenced. They pop into place properly if the map is georeferenced. I usuallly start projects by importing some OSM data and then geoferencing it (and often adjusting for magnetic north) and then open KP files and templates.

You shouldn't have to manually adjust any of the KP outputs unless there's something off with the georeferencing of the map.

The outputs from LAStools (like blast2dem) will generate a .png and .pgw file at the same time. So they will also be georeferenced.

I'm not really sure of the best sources for air photos. The National Map Viewer used to have pretty good photos, but I think the best you can get from that source now are the NAIP images. Those are ok, but not great.

I know it isn't helpful for you, but for Kansas they've got pretty good 2014 air photos with the leaves down at www.kansasgis.org

If you haven't done so, watching some of the LAStools turtorial vidoes might be worth doing. I found them pretty good and I remember that I learned from watching them and following along at the same time.

You might take a look at the Map Puzzle software: http://www.mappuzzle.se/

Map Puzzle lets you download georeferenced images from a bunch of sources, including Google and Bing. There's something odd about the way it georeferences if you click the UTM button. The work around is to use lat/long geoferencing and then use some other software (like Global Mapper or QGIS) to change it to UTM.

With some work to tweak settings and some good lidar data, I really find the vegetation mapping from KP useful. Especially in Kansas-terrain I can get shades of green that work pretty well. Since that's the hardest part of mapping around here, it is a big help.