Lidar

The Third Day of XYMas – GRASS

rjhale · Dec 18, 2019 ·

I know – I’m running behind. So look at these 12 days as either “hints” or “tools”….or both. Being a consultant I walk into some weird situations with data and clients – so it helps to take a full complement of tools into a situation….and a good attitude but that’s on Day 12.

So what do I give you on day 3? GRASS. Yeah and it’s the running joke EVERY.SINGLE.TIME. “I tried GRASS back in College”.

If GDAL is a swiss army knife and QGIS is my hatchet – this is my sledgehammer. I may not use it as much as I need to – but when I need it it works oh so well.

GRASS has been under some form of development since 1982. It was opened up in the mid 90’s and it’s still actively developed today. Python friendly. Command line friendly. It has it all – even a friendly gui so you can push buttons.

So what do I use it for? If you’re an active QGIS user you’ll see a lot of the tools exposed in the processing toolbox. You can gleefully play along with it there if you wish. I would encourage you to look at the tutorials the community has provided. If you’re dealing with a lot of raster data it’s pretty awesome. I’ve used it for drive time analysis with vector data. My one secret weapon with vector data has been the topology tools. If I receive some really bad vector data I’ll import it into GRASS and clean it up. Yes – for those of you that miss clean and build from your workstation days you can relive some of that excitement here.

A couple of years ago I had a call from a drone company. They wanted to leverage their raster data beyond the commercial software they were using. They wanted multiple products with multiple use cases and a lot of clients all from a server out in the “cloud”. My answer? Something really complicated involving some weird process? No – the Second worst programmer in existence (me) hammered out a process leveraging GRASS and python. We were adding and subtracting elevation models after some hefty discussion using the processes found in GRASS. which to me was somewhat poetic – this, probably the oldest piece of software I use, was working with Drones, probably the most disruptive thing to hit aerial imagery collection in forever.

Right now I’ve been using it with LIDAR data. TN freed up a lot of LIDAR data (points and a surface model) for people to work with. I have been known to download the data and mosaic it with GRASS. I’ve played with point clouds in here also. One of the best thing about GRASS is it’s rock solid. I’ve not crashed it often and I really have to do something super stupid to make it go down. If I want to toss a few hundred GB of raster data at it that’s fine as it will churn through that data without blinking.

On Day 3 – Try the Geographic Resources Analysis Support System software. The Ultimate why?

Captain Kirk said so….

Class, GRASS, and LAS – LIDAR in TN Part 3

rjhale · Jul 6, 2017 ·

And now for Part 3.

So something exciting happened. If you’ve been keeping up with the TN GIS Data site you’ll notice a lot more data has been released in uncomfortably HUGE zip files. I downloaded two counties worth and have been exploring the data. In the meantime I started getting a few emails of “hey we’re getting data on a hard drive”. The cool thing with that is I received a tile from a county and it’s in LAS. If you read through some of my other rants I’ve been annoyed by the fact this is in zlas format. If you do some digging on zlas it’s more or less ESRI going “Hey we’ve made a format that only we use” and you have to unlock it to make it useful by anything else. We’ll – the counties are getting unlocked data. Victory.

BUT – there’s one more Problem. In all my examples I’ve been using GRASS. So I tried to pull the data in and nothing good happened. Actually – nothing happened. It was then I started learning about liblas and the LAS Library Versions. The short story is GRASS will read the 1.2 LAS Version. The data provided by the state is in 1.4. So you can’t automatically use GRASS to do anything with the data.

EXCEPT PDAL TO THE RESCUE! Probably the one thing I’m learning is I’m not short on tools to use with LIDAR. I’m up to: GRASS, PDAL, SAGA, and LASTOOLS. I will spare you all the information on how to get PDAL – read about it on the website. For those of you on Windows: if you have QGIS from the OSGEO Network Installer, you can download PDAL painlessly and be quite happy. As I’m running Linux on everything I grabbed a copy and compiled it and have it locally. I’m also quite happy with that.

So the one thing you need to know is this: pdal translate inputlasfile outputlasfile . Issue that command from the OSGEO window. Something wonderful happens – you get a LAS file v 1.2 you can run through GRASS.

You can do things like making a map of the intensity values:

Or a hillshade for posterity:

To get from an LAS file to anything above is about 10 minutes. Maybe 12 minutes. I’m running this on a laptop with a lot of RAM – but I could do this on a much lower end machine.

I’ve covered GRASS and LAS….Oh Class! Read your metadata. If you read Part 2 above you’ll notice there is a change in Classification with the new data:

Classification	Value
Unclassified	1
Bare Earth	2
Low Noise	6
Water	9
Ignored ground	10
Bridges	17
High Noise	18

…and there – I finished my horrific joke of LAS, GRASS, and Class. I’m not explaining it.

It’s happening. LAS files for TN are out and about. My first thought is what can I do with this….my second is what are you TN Citizens going to do with it. My first two requests have been:

How do we get Tree Height?
Can we see Archaeological sites?

So – my next goal is to process A LOT of LIDAR at night. I’m going to set up a process to fix the format (unfortunately the data on the States website is still zlas), fix the library version, and then process a lot of data. Overnight? During the day? Who knows.

Georgia URISA Luncheon – January 10th 2016

rjhale · Jan 5, 2017 ·

LIDAR is a hot topic in Georgia these days. So – for the January 2016 Luncheon more LIDAR.

“LIDAR Updates – Changes in the Technology and Coverage”
Speaker Name: Ernie Smith

Presentation Summary: Like all Technology LiDAR has become very dynamic with new sensors and available data. We will talk about the advancements and availability of Sensors, Standards, and Data sets. There are many changes in the technology and unless you are working with it everyday, it’s difficult to keep up with all of the advancements.

Standards are also changing due to the sensor technology advancement which means practices and applications for LiDAR are growing. Also drones are being used for data collection and there are some things to be aware of for that use of Technology. We will present a map that gives our best understanding of where LiDAR data exists in Georgia as well.

Location:
Henry County Water Authority (Engineering Building)
100 Westridge Industrial Boulevard
McDonough, GA 30253

Georgia URISA November Luncheon November 8th 2016

rjhale · Oct 25, 2016 ·

Speaker Name: Jimmy Nolan

Speaker Bio: Mr. Nolan began working with GIS in 1994 when he was the chief appraiser for Morgan County. In 1999 Jimmy went to work as the GIS specialist for the Georgia Department of Revenue. In 2001 he became the local government project manager for the Information Technology Services division of the Carl Vinson Institute of Government at the University of Georgia. Since joining ITOS he has been instrumental in helping develop GIS in approximately 50 counties and has worked with local officials in many more counties and cities to enhance data or provide advice and training. Jimmy is the Cadastral Coordinator for the state of Georgia and was on the Federal Geographic Data Committee technical working group that developed the parcel data content standards for the eastern 31 states. He is the immediate past chairman of the Georgia GIS coordinating committee and a former Ga. URISA board member. He has extensive knowledge of how Computer Assisted Mass Appraisal systems model property values and how the data used in these models is organized as well as how these systems integrate with GIS.

Presentation Summary: The presentation will cover:

Current initiatives
Upcoming LiDAR acquisition projects
Coordination between multiple agencies at all levels of government
The 3DEP grant application that the state has submitted.

Additional Information:

Join WebEx meeting
Meeting number (access code): 927 999 105
Meeting password: URISA

Join by phone
+1-855-282-6330 US TOLL FREE
+1-415-655-0003 US TOLL
Location:
Hexagon Geospatial
5051 Peachtree Corners Circle
Norcross, GA 30092 USA

Adventures in LIDAR and GRASS in Tennessee: Part 2

rjhale · Aug 31, 2016 ·

Sometimes it takes a while to follow up on a blog post. A while back I wrote more or less “I got me some LIDAR what can I do with it?”. Well…..

First I need to learn about LIDAR and at some point (probably during Part 3) names will be named. There have been several people in the FOSS4G world helping me move along and learn.

Second thing I needed to do was ask questions. I asked a lot. I learned:

TN has been participating in 3DEP. So this LIDAR Data (as well as several other products) are coming from that program.
I need to read metadata.

So when I left you on my original post I was importing LIDAR into GRASS and somewhat failing miserably. After reading the metadata the point data was classified as follows:
Class 1 = Unclassified. This class includes vegetation, buildings, noise etc.
Class 2 = Ground
Class 7= Noise
Class 8= Model Key Points
Class 9 = Water
Class 12=Overlap Points (high scan angles)
Class 13= Bridge Deck Points

So this gets a little bit easier. Using v.in.lidar I can now build a DEM and pull the values coded for bare earth straight in.

Hillshaded for posterity:

Once I started “playing” fun things started happening. I know this isn’t 100% right because I have more to learn. What if I import LIDAR data coded as vegetation and subtract that from the DEM. I have Vegetation height. With the Ortho image I can shove more knowledge toward my foresters. I also have some negative values I’m going to investigate.

You may be going “Well that’s great you’re sitting here doing crap anyone can do”. Possibly. For a small entity with limited budget you can whip out GRASS and start doing things. This was a 10 minute endeavor for one tile. I also generated slope and I’m working on building a solar radiance map of the area. Now I want to process the entire county for elevation. Can I? I will also dump this out to QGIS because I can.

The big kicker in all of this THIS IS FREE DATA. Well – except for the zlas problem. State of TN – take the lead and open the format for the users. Switch to las.

So what am I doing for Part 3:

Upgrading GRASS to 7.2 (I’m running 7.0.4)
Count LIDAR points on the ground – the metadata claims one point per meter.
Will someone give me the RAW data? I’m attending a conference where people of influence will be – I’m going to ask.
UAV?
Building Height with elevation above ground?

I have a lot to learn and I am by no means an expert. LIDAR started getting popular about the time I walked out of my federal job and I never have clients that go “We’ve got this data sitting around”. I’ve never had to deal with it but now that I have a source to work with there’s a lot I can do. I have a community of people that will answer questions when I have them. Never stop learning.

Anyway – Part 3 is coming and it won’t take months for me to get to it.

Lidar

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