I'm still developing a control network upon which to base a detailed topo gathering project, as part of my on-going education. I've been bringing traverse segments into the survey in bits and pieces, and putting them together. I decided to try to apply what I've read on coordinate transformation, (grid/ground, SPC, etc.) to practical use and need some guidance. Project is small (2000' end to end); That might be a factor, in that I want to learn proper procedure more than having numbers accurate to 6 digits. I've played with the factor though and can see what might be significant differences for long shots (500' or so).
I've moved the survey to Vermont NAD83 Conus; it comes up with a scale factor of .999964286. I've output some of the points in the survey as Control points, and now that the survey has been moved, so too are the control points.
But in SurvCE, the "localization" screen says:
"For most applications, the Scale Factor should be set to 1.0 to work on the ground with a total station. The scale factor represents the combined grid/elevation factor that reduces ground distances to grid."
I'm obviously measuring ground distances, but is the fact that the control point coordinates have been calculated using the SPC scale factor mean that this is improper? Should I apply the same scale factor in the DC when gathering new data? I have read that it's way better to "just deal with this in the office", but what is the best practice for moving points back and forth from office to field?
RFC,
There are more ways to accomplish what you are doing than members on this board. We each no doubt have favorites. In reality we should all probably be using a variety. letting the circumstances drive the method.
It is getting very common for the field 'crew' to gather raw data in whatever format is most convenient, then let the office guys smash it up. That can be a profitable business model in some places but it doesn't teach the crew anything.
We run most of our jobs on State Plane Grid or custom projections. If on Grid we apply the CAF in the field. This maintains a good working grid file and expresses things at ground for the crew. The raw data is unadulterated raw.
You want to be careful with your terms and associated numbers. If you key in the factor (in the version we use anyway) it is keyed in as the inverse of the combined factor. As I recall you can reverse this setting. The idea is to get working ground information while in the field but have clean data for the office to process and QC. Regardless of how the crew views our data is collects the 'as-measured' data.
Hope that helps, Tom
rfc, post: 326000, member: 8882 wrote: I'm still developing a control network upon which to base a detailed topo gathering project, as part of my on-going education. I've been bringing traverse segments into the survey in bits and pieces, and putting them together. I decided to try to apply what I've read on coordinate transformation, (grid/ground, SPC, etc.) to practical use and need some guidance. Project is small (2000' end to end); That might be a factor, in that I want to learn proper procedure more than having numbers accurate to 6 digits. I've played with the factor though and can see what might be significant differences for long shots (500' or so).
I've moved the survey to Vermont NAD83 Conus; it comes up with a scale factor of .999964286. I've output some of the points in the survey as Control points, and now that the survey has been moved, so too are the control points.
But in SurvCE, the "localization" screen says:
"For most applications, the Scale Factor should be set to 1.0 to work on the ground with a total station. The scale factor represents the combined grid/elevation factor that reduces ground distances to grid."I'm obviously measuring ground distances, but is the fact that the control point coordinates have been calculated using the SPC scale factor mean that this is improper? Should I apply the same scale factor in the DC when gathering new data? I have read that it's way better to "just deal with this in the office", but what is the best practice for moving points back and forth from office to field?
In the DC, everything is on the surface (conventional traversing). It keeps everyone doing what they already know. However, when I reduce the raw data in Carlson, I tell it to apply the scale factor and calculate it at each segment. That way, that which is collected is surface and that which is in the computer is on the grid. I do not mix and match, even with a scale factor like you have.
Kris Morgan, post: 326019, member: 29 wrote: In the DC, everything is on the surface (conventional traversing). It keeps everyone doing what they already know. However, when I reduce the raw data in Carlson, I tell it to apply the scale factor and calculate it at each segment. That way, that which is collected is surface and that which is in the computer is on the grid. I do not mix and match, even with a scale factor like you have.
I guess what I'm asking is this: I set up on the last point from the previous day and backlight to the second to the last point from the previous day, both of which have been brought in, transformed and output as "control points". So let's say they were 1000,1000 and 2000, 2000 when they went in, and 999.999,999.999 and 1999.999, 1999.999 (just making up numbers) when they show up in the control file on the DC.
If I measure the backsight distance between them, it's going to be "wrong", wouldn't it? Are you saying:
A) "don't worry about it, because when the new ground distances come into the office, they'll be similarly adjusted"...or
B) "adjust away in the office, but when you send control points back out to the DC, 'unadjusted them' (by doing a "grid to ground" transformation)".
Firstly, I try to complete the field work in stages, i.e. collect all data and then reduce.
On the rare occasions where I HAVE to calculate and then go back to the field the next day, I'm using method "A" because it won't adjust those values again, only the new observations from those points when I reduce the data.
Does that make sense?
If we are talking about a control loop, then I don't do anything until I get it in the office other than field calculations for looking for corners or something.
I'm way better with a cold Dr. Pepper at my drafting desk than I am in the field sweating like Fat Elvis trying to keep production going, as far as calculating goes.
rfc, post: 326000, member: 8882 wrote: .....I've moved the survey to Vermont NAD83 Conus; it comes up with a scale factor of .999964286. ....But in SurvCE, the "localization" screen says:
"For most applications, the Scale Factor should be set to 1.0 to work on the ground with a total station. The scale factor represents the combined grid/elevation factor that reduces ground distances to grid."
As I understand it, you have control coordinates that are on NAD83 Vermont State Plane, and you wish to collect data and get coordinates that are on NAD83 Vermont State Plane.
Set the projection in your dc to NAD 83 Vermont State Plane. (DO NOT try to force some scale factor.) Your dc will make the appropriate calculations and your resultant coordinates will be "on the grid". The raw data will be ground measurements .
I checked the "System" tab in "Job Settings", and it's been on "USA/NAD83/VT" all along. If I understand it correctly, I'm "good to go" the way I'm doing this, according to your comment.
I'm not sure what the "scale factor" under the instrument tab is then, unless it has to do with the "curvature and refraction" and/or "sea level correction".
I'll leave that at 1.00000
As for Kris' comment about "collecting all the data, then reducing": in my case that's just not an option. I have only nights and weekends to do this, and as it turns out, most of the time lately has been in the office trying to correct the screw-ups I made in the field. So back in the field I go to correct the errors and around and around we go (until I get to a point that I have a good, methodical, proper process down, anyway).
