target height w/ a C10

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Brandon_Vogt
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target height w/ a C10

Post by Brandon_Vogt » Wed May 09, 2018 6:36 pm

Greetings. This is my first post - nice to meet you all....

I have a C10, I only free-station, and I use the HDS system exclusively outdoors over natural landscape surfaces (to model gullies, fluvial deposits, archaeological sites) – mostly for graduate student projects. My questions are about best-practice for target use for registration:

1. With twin-target pole systems (I own three), is it advisable to select (using pull-down menu) target type (e.g., twin-target pole top / twin-target pole bottom)? I’m wondering about this because, over a rolling, rough landscape, how is it beneficial for Cyclone to know the (relative) height of the target top and/ or target bottom above a surface? I’ve struggled with this b/c height is not specified with, for example, blue tilt & turn targets, which I also use.

2. Related to question 1, for each twin-target pole, is it advisable to include both the top AND the bottom target on each pole system as targets? Maybe this helps with the scan-to-vertical element of registration?

Thank you anyone who can help shed some light on these basic ‘target’ questions.

Brandon Vogt
Colorado Springs, CO

Jamesrye
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Re: target height w/ a C10

Post by Jamesrye » Thu May 10, 2018 8:41 am

Hi Brandon,

You only need to record the height of a target if you're setting it up over a known point - to coordinate your data. We have a couple of those twin target pole systems - I really don't like them - much better to use a 6inch target on a normal tripod in my opinion. The larger target lets you scan it from further away and you wont pinch your fingers using that twin pole system.

James

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James Hall
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Re: target height w/ a C10

Post by James Hall » Thu May 10, 2018 5:42 pm

Hello Brandon,

I have found the C10 to be a little hit and miss with finding the center of targets and end up double checking the targets in Cyclone. (This is especially true for sphere targets) Often the residuals will be good in the C10 but the vertexes will be off in Cyclone. Check each of the HDS Target Scans to make sure the Vertex is centered and if it is not just refit it to the cloud.

In the field I prefer to use a fixed length rods and spheres. We shoot in the control points with RTK GPS and enter the coordinates into the C10. Do our first scan and switch to free station scanning. When I encounter my next pair of control points I set up near them (Within 30 ft) instead of doing a target scan with Entered coordinates. On the last scan I tie into two control points with entered coordinates from our GPS like with the first setup.

The control file from the GPS is added to Cyclone as the Home Scan would. I use the "Auto add control points ID only" command to line up the scans so automatic cloud to cloud constraints can be used to tie the seen together. For the free station scans with control I open the Control Space and add the targets by fitting to the cloud. (This is a quick process in the office and cuts my setup time down in the field) In the field I can get 8 to 12 setups an hour with this method. Entering coordinates for every setup slows me down to 3 or 5 setups an hour.

If you enter coordinates for every setup foresight and backsight the control need to be set at 100 to 150ft for 6 inch spheres and for the twin Target poles the control is set 60 to 80 feet max.

1. The twin-target pole. (Make sure you assemble the target correctly or is will not mach the predefined pull down) The height of target is predefined in the pull-down menu. Otherwise you need to enter the HI as with your Blue tilt and turn targets. If you are not occupying a control point the HI is not necessary.

2. I use the bottom target as it is closer to the ground with less error do to leveling the rod. I window scan the top target only as auxiliary control.

James Hall,

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Re: target height w/ a C10

Post by Brandon_Vogt » Thu May 17, 2018 3:48 am

James H and James R: Thank you very much for the replies. Some helpful tidbits of info. in your posts for sure. I'm very happy to have this new resource (laserscanningforum). Sincerely, Brandon Vogt

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