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May 02 2012

First Group Field Day

On Saturday 4/29/2012 we had the first field day of the semester. The goal was to begin mapping the trees at HR and to perfect our methods. However we soon discovered that our 5x5 meter plots that had been previously marked with PVC had much more error than we anticipated. To accommodate this we mapped the trees in the corners of 25x25 meter plots because they contained the known survey points.

We managed to get 8 of the 5x5 Meter plots surveyed and ready to document. Also, we have determined a new method to plot the 5x5 meter subplots. Our error came from one main source. When we were measuring the 5x5 subplots we started by marking the perimeter. Once this was done we laid out a string across the plot and measured along the string to mark our subplot points. While the points were 5 meters apart in one direction they were not in the other. The reference string did not provide enough accuracy and would lead to a line of points which fall to the left or the right of where they should fall.

To tackle this problem we purchased a straight line laser that can shoot up to 1000ft. The idea behind this is it will give us a perfectly straight reference line. We will shoot the laser across the plot from one known perimeter point to the next and than proceed to mark the points within the plot that lay on this line. This will hopefully do away with the error that accumulates while measuring along an inaccurate reference line.

At the end of the day we learned allot about our methods and what needs to be improved. This is all a part of field work to design, test, and redesign. Hopefully we will have another group field day soon with corrected subplots allowing much more mapping to be accomplished. I want to thank everyone from the ecosynth team and volunteers who made this day possible. 

Apr 09 2012

First Test of PVC Markers


On Thursday 4/5/2012 Jonathan and I went to HR with 2 other students to attempt to lay out the PVC pipe that will mark the 5x5 meter grid. Our plan was to lay a reference string between 2 of the serveyed points in the 25x25 meter grid. Once this was done we could measure 5 meters along this line with our wooden poles, string, and line levels to help ensure accuracy. We secured a string between the two wooden poles measured at 5 meters We would than insert PVC poles like the ones to the left at these 5 meter marks. However when we finished our first 4 points and came to the known survey point we were anywhere from 10 to 30 cm off. This was too much inaccuracy and we quickly saw that the string connecting the two wooden poles could flex, this being our cause of inaccuracy, we determined we needed a more rigid material to connect the poles. Back at the lab we found some thin metal wire and after attatching this to the wooden poles and retesting the same strategy as before the accuracy was greatly improved, at most we had a 1 to 2 cm innaccuracy with most of the corner points we plotted landing directly on the survey point.

Mar 27 2012

Topography and the Mapping Grid

There has been a new data sheet designed to address the specific needs of the forest we are working with. Because the method for mapping the trees has changed, the data sheets also needed to be altered. We are returning to the previous used method of laying out a 1x1 meter grid within our 5x5 meter grid. Once this is complete the location of the trees will be marked on the graph found on the data sheet. There has also been a "codes" column added to the data sheet to represent trees that may need special attention. This could include a leaning stem, a stem broken below breast hight, or as seen in the picture multiple stems from one trunk forming below breast height. However, before the trees can be mapped the grid must first be sectioned into 5x5 meter squares. Jonathan, fellow students, and I are hoping to get one of the 25x25 meter plots sectioned off so we can begin to test our tree mapping stratgies. We are also tackling the problems we may face concerning drastic elevation changes. In summary we have all of our supplies ready and in bags we just need to find a time to get dirty and see how our ideas work.


 

Mar 21 2012

Tree mapping Technique

There have been many methods for mapping the trees within our 25x25 meter grid that we have identified. The one certatinty we have decided on is the grid must be sectioned into a 5x5 meter grid before we can begin mapping. The picture on the left shows a method found in the field guide Methods For Establishment And Inventory Of Permanent Plots. This method involves usining geometry to determine the exact point of a tree and we thought it could be more accurate and faster than other ideas. However when we went to our forrest to test we discovered that it was not only more tedious but may not improve accuracy by a reasonable amount if at all. The problems arose when we needed to take measurments on unlevel surfaces. It would involve 3 or more people with much instruction and using handfulls of equpment, it was uneffective for our purposes. We plan on going on another test run before the week ends to try another method that will hopefully work for what we need. 

References:

Dallmeier, F. (1992). "Long-term monitoring of biological diversity in tropical forest areas." Methods for establishment and inventory of permanent plots. MAB Digest Series, 11. UNESCO. Paris

Nov 01 2011

Personal remote sensing goes live: Mapping with Ardupilot

Folks all over are waking up to the fact that remote sensing is now something you really should try at home!  Today DIYDrones published a fine example of homebrew 3D mapping using an RC plane, a regular camera, and a computer vision software: hypr3d (one I’ve never heard of).  Hello Jonathan!

 

PS: I’d be glad to pay for a 3D print of our best Ecosynth- hypr3D can do it, so can landprint.com

Oct 14 2011

Mikrokopter and Computer Vision/Photogrammetry used for Landslide Modeling

Researchers at the Universität Stuttgart, Institute for Geophysics in Stuttgart Germany, have used manually flown Mikrokopters and semi-automated photogrammetric software to generate high resolution photo mosaics and digital terrain models of a landslide area for tracking terrain displacement.  

An article published this spring in the journal Engineering Geology demonstrated the value of using remote controlled aircraft and off-the-shelf digital cameras for high resolution digtial terrain modeling.  The researchers used photogrammetry and computer vision software VMS to make 3D terrain models with aerial images and compared the results to aerial LIDAR and TLS terrain models.  A network of ~200 GPS measured ground control points were used to assist with image registration and model accuracy with good results.

The authors appear to agree with our sentiments that RC based aerial photography and 3D scanning has the benefits of low-cost and repeatability compared to traditional fixed wing or satellite based data collections.

Unlike our research, the authors of this study were interested in only the digital terrain model (DTM) and vegetation was considered noise to be removed for more accurate surface modelling.

Again...just one more reason for me to get cranking on that next paper!

Image source: http://commons.wikimedia.org/wiki/File:Super_sauze_landslide.JPG

Aug 03 2011

Kinect 3D Scanning for Archeologists

As we’ve seen before, Kinect 3D scanning keeps getting more popular all the time, including for outdoor work in the sciences:  “Archaeologists Now Use Kinect to Build 3-D Models During Digs”.

 

Still some clear and major issues with using the Kinect outside and for scanning forests, maybe it is time to give this a try in the lab?

Apr 07 2011

Open Source Terrain Processing

I am very excited by the current prospects of incorporating free, open-source terrain processing algorithms into our workflow.  While we are ultimately interested in studying the trees in our 3D scans, it is necessary to automatically derive a digital terrain model (DTM) that represents the ground below the canopy for the purpose of estimating tree height.

A recent paper in the open-source journal Remote Sensing, describes several freely available algorithms for terrain processing.  I am in the process of converting the entire ArcGIS workflow we used in our first paper into an automated Python workflow, and am excited about the prospect of incorporating other open-source algorithms into the mix.  Currently, by working with Numpy in Python, my processing code takes a input Ecosynth point cloud and applies two levels of ‘global’ and ‘local’ statistical filtering to remove outlier and noise elevation points in about a minute for 500,000 points.  This had previously taken hours with ArcGIS, but by formatting the data into arrays, Numpy effortlessly screams through all the points in no time. 

I am going to focus on two pieces of software.  One is the Multiscale Curvature Classification algorithm (MCC-LIDAR) by Evans and Hudak, at sourceforge here, that was mentioned in the recent paper in Remote Sensing.  The other is the libLAS module for Python, included with OSGeo, that can be used to read and write to the industry standard LAS data format for working with LiDAR data. Fun, fun!  This of course if going on in the meantime while I try to get my proposal finished.

Refs: 

Dandois, J.P.; Ellis, E.C. Remote Sensing of Vegetation Structure Using Computer Vision. Remote Sens. 2010, 2, 1157-1176.

Tinkham, W.T.; Huang, H.; Smith, A.M.S.; Shrestha, R.; Falkowski, M.J.; Hudak, A.T.; Link, T.E.; Glenn, N.F.; Marks, D.G. A Comparison of Two Open Source LiDAR Surface Classification Algorithms. Remote Sens. 2011, 3, 638-649.