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How to input laser rangefinder data into GIS

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#1
Carri Marschner

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Greetings,

The lab I work for has most of their map data in laser-mapping format from a laser surveying tool (LTI Impulse). My task is to get this data into GIS. I have points that are both laser and GPS mapped throughout the data set, so I have reference points, but laser data is all in the format of x,y,z coordinates from an arbitrary starting point.

The questions are:

1) Is there an already-determined method/tool for doing this?

2) If I need to triangulate each point, I will be starting from a fixed point and placing each point (eg, five meters north, seven meters east, .2 meters up). Is there a place I can look up how to shift a given distance for each projection?

3) (Newbie question) I'm sure there's a term for what I'm trying to do - georeference a data set, perhaps? If there is a term, I'd be grateful to know what it is so I can search the archives more effectively.

4) Are there pitfalls I should be aware of during this process?

Thank you for taking the time to look at this question. I hope that I haven't overlooked an existing post covering this; if so, my apologies.

Sincerely,

Carri Marschner
Carri Marschner
Cary Institute for Ecosystem Studies
Millbrook, NY
www.caryinstitute.org

#2
Nick H

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Hi Carri,

Forgive me, I'm not sure exactly what what you wish to do. As I read it, you have some reference points (as eastings and northings) determined by GPS and some distances measured from the reference points, determined by using a laser range finder. What you want to do is to plot in GIS the positions of the points that you measured with the range finder?

My other assumption is that your range finder produces data that can be used to calculate horizontal distances from slope distances (such as when you are measuring distances up the side of a hill).

Do I have this somewhere about right?

Your Point (2) above suggests you might be doing a traverse of some kind, but I'm not sure about this :).

Regards, N.
Caversham, Reading, England.

#3
jrat

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It is late to say now, but it is possible to set up arcpad on your gps unit with a range finder and capture offset points on the fly.

In the data set you are working with you have a gps fix as the origin for each range finder shot, right?

I don't know of any existing tools that will do this for you. If all the data is in a grid format then a simple move by field script might work. (I have no Idea how to write it). Assuming your data has an x,y and Δx,ΔY for each entry.

#4
Nick H

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It is late to say now, but it is possible to set up arcpad on your gps unit with a range finder and capture offset points on the fly.


Ah... I see! (I think.) It's offsets from a base line connecting two reference points, that makes more sense. There's good, free software for handling data from surveys carried out by measuring offsets.

Map Maker has a good, simple set of features for handling survey data. A while ago I wrote a (quick and horrible) explanation of how to plot offset survey data in Map maker, see Page 4:

http://confound.me.u..._by_example.pdf

The free version of Map Maker will do all of this, but in fact as downloaded MM will work in fully-featured mode for 28 days.

Regards, N.
Caversham, Reading, England.

#5
Carri Marschner

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Thanks to both of you for your responses. I will look into the MapMaker and see if that will help.

For clarification, we are mapping all the trees on six one-hectare plots. The PIs opted for laser mapping when sub-meter accuracy in GPS wasn't readily available, and now would like to shift that data set into GIS. I'm attaching an file with data from one location (txt, tab delimited) and the associated map (power point, first slide), so you can see what it looks like. We have GPS points for the corners of the area, which are where the crew started mapping, so somehow I should be able to tie all the tree locations into the origin point (lower left, in this case).

I hope that makes the project clearer, rather than more confusing. Thank you for your input on this.

Sincerely,

Carri Marschner

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Carri Marschner
Cary Institute for Ecosystem Studies
Millbrook, NY
www.caryinstitute.org

#6
Carri Marschner

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Nick,

I'm afraid it's not offsets from a line, or open or closed compass points. It may be distances from a fixed point. I've attached a diagram of how the data were collected. -Carri

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Carri Marschner
Cary Institute for Ecosystem Studies
Millbrook, NY
www.caryinstitute.org

#7
Nick H

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Hi Carri,

Okay, I think I might understand :). It's compass bearings and distances measured from points of known position. One way of doing the calculations would be to use COPAN, it's free, see:

http://www.underhill...ws/CopanWin.php

and in particular:

http://www.underhill...20Azimuths.html

Excellent though it is I find COPAN fairly hard work and overkill for my needs so for a job like this I'd use Map Maker, see Page 237 of the manual:

http://www.mapmaker....oads/manual.pdf

Regards, N.
Caversham, Reading, England.

#8
Carri Marschner

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Nick,

I'm happy to hear that I'm starting to make some sense :) . It looks like either MapMaker or COPAN will help me map/place the points in relation to each other; will either program get them into, say, NAD 83 so I can place them in an .mxd?

Thanks so much for the advice. I think I'll probably go the MapMaker route if it can do what I need it to; it looks less intimidating.

Carri


Hi Carri,

Okay, I think I might understand :). It's compass bearings and distances measured from points of known position. One way of doing the calculations would be to use COPAN, it's free, see:

http://www.underhill...ws/CopanWin.php

and in particular:

http://www.underhill...20Azimuths.html

Excellent though it is I find COPAN fairly hard work and overkill for my needs so for a job like this I'd use Map Maker, see Page 237 of the manual:

http://www.mapmaker....oads/manual.pdf

Regards, N.


Carri Marschner
Cary Institute for Ecosystem Studies
Millbrook, NY
www.caryinstitute.org

#9
Darren Rattai

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Hello Carri,

My company uses high end laser range finders that talk to our Trimble GPS units via bluetooth that automatically updates to the exact location of the laser's point through determining slope distance, inclination and bearing.

I know this is a little late for this particular project, but if you would like some more information from me for future proejcts on the tech we are using, please let me know. This system has been working flawlessly for us so far.

Cheers,
Darren

#10
Carri Marschner

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Conclusion:

So I wound up collecting the data from the rangefinder and running it through some programs a scientist on staff had written; one did the basic trigonometry to change from bearing/distance/azimuth to x/y/z in UTM NAD 83 zone 18 and another hooked the trees to control points. It projected nicely. Thank you all for your help.
Sincerely,

Carri Marschner

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Carri Marschner
Cary Institute for Ecosystem Studies
Millbrook, NY
www.caryinstitute.org




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