How to get my projections and transformations to work together to produce the results I am needing in Collector and AGO

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09-05-2019 01:31 PM
LisaRayburg
New Contributor

ArcMap is shifting my GPS points that I collect in the Collector App to the South East about 2-6 feet.

I am comparing my shots with Survey points from my survey department.

I have tried numerous GCS and projections....i am seriously running out of steam here.... I do not know what else to GOOGLE to give me the answers i need. No one seems to have the answers. I had my trimble Rep here trying to help me, i have a Case open with ESRI, no one seems to know whats going on...

to say i am frustrated is understatement.

Anyone else run into this issue in the past?

We use a local SITE coordinate system... and not many people use these... if this is something that rings a bell to you, can you please help me out? Lance Cole‌ i was thinking from reading your stuff that you may be someone who has used a Site coordinate system before...

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5 Replies
LanceCole
MVP Regular Contributor

Lisa, 

The joys of coordinate systems and transformations.  For most, persistence has payed off but this can take some time, a lot of time.  There is a lot going on with a high accuracy GPS and Collector.  First there is your GPS that is working on a given coordinate system and datum, you are then applying a local site correction to this data to zero in the accuracy and/or use a custom coordinate system, this data is then passed to Collector either directly or with an initial transformation within the GPS or its application, Collector then takes this information and applies additional transformation(s) to display the data and/or post it to AGOL or your own enterprise site,  then you are accessing this data and again applying more transformations to get the data where it needs to be.  Lots of room to loose track of everything that has been applied so understandable that it is confusing.

Here are some thoughts as I think through the issue you described.  You do not really need to answer but you are welcome to.

1) I have not had the opportunity of working with a local site system using Collector.  We do have a site system setup for our surveyor but for GIS we typically run off the State VRS system.  However, the first thing I would confirm is that your local corrections are getting applied to your base coordinate system and this info is getting sent to Collector and not just the raw GPS data.  Especially if these corrections are close the error you are observing. The error is rather large and I would guess your corrections are not that large unless you are also including a transformation at that point.

2) Was the correct base coordinate system selected for your GPS and was the local site configured correctly? Also look at units such as meters vs international feet vs US feet.

3) How does collector work with local site corrections? Is it exclusively handled in the Trimble software before passing the data to collector?  What data is being passed to to Collector? Is the corrected data getting passed or the uncorrected?

4) What data is stored in the ESRI GNSS metadata (Latitude, Longitude, Altitude) when collecting a point?  Is it the base coordinate system data or the local site corrected data?  Have you tried restoring the points back from the metadata to see how they place in relation to your surveyors control data.  

Other considerations

1) confirm the coordinate system your surveyor is using and that these points are correct once brought into the GIS system you are working with to view the data. Do you have imagery of high enough accuracy to confirm against?

2) confirm what coordinate system the data being stored in the ESRI GNSS metadata for Latitude, Longitude and Altitude.  This is the raw coordinate data from the GPS less any transformations and will be height above ellipsoid for the altitude data, not elevation.  I do not know if this will contain the corrections for your local site.  You may want to check with Trimble on that item.  I really need to get a loaner from Trimble this winter to learn more about their units.

3) try and use this raw data and applicable transformations to get your data into your system with minimal transformations being applied.  The ProjectZ tool is great for this initial process.  This typically eliminates anything that may have been applied by Collector, AGOL or when pulling your data back into a local system.

4) load in your surveyors control data and have your coordinate system set for the data frame first.  Bring in your problematic GPS data and experiment with different transformations on your raw data. I prefer to do this using ArcGIS Desktop 10.x as you have more fixed control of the transformation being applied (may just be me and having used Desktop for decades).  ArcGIS Pro can automatically apply transformations that are not necessarily the correct one to be using.

5) note how the different transformations shift your data.  You may just find one that works.  You may note one moves the data up and down, another moves the data left and right.  You may need to perform one to move the data up and down then apply one that moves the data left and right.  That is how we found we needed to use two transformations to go from NAD83 to NAD83(2011) for our State Plane System.

6) use logic, there are hundreds of transformations out there but most can be eliminated by simply looking at what system am I starting from and where do I need to go.  

7) any chance your local site corrections or a transformation is getting applied twice?

If you can provide a sample of your data, surveyor control data and the coordinate system info I would be glad to take a look.  That’s what weekends are for, right.  Sorry, I do not have a specific solution but you can do this.

Have a great evening.

LisaRayburg
New Contributor

Lance Cole Thanks for the response!

#1 - I do not have the SITE set up to be used in Collector. I have not figured out how to do so.. (ESRI is looking into this). I also connect to the VRS. Do you use SPace as the means of connecting to the VRS while using Collector? I would think i am doing the process correctly when checking to make sure the local corrections are being made.. i check inside of the SPace app.... I check for the connection to be made... If there is another way, just let me know...

#2- The local site was not used in Collector. I have created soooo many location profiles inside of collector, I've probably tried every option!! JK but to name a few that I have used - WGS 1984 Web Mercator Auxilary Sphere, NAD 1983 2011 UTM Zone 17N, NAD 1983 HARN StatePlane Ohio North FIPS 3401, NAD 1983 StatePlane Ohio North FIPS 3401, and the default....

#3 - this was answered in above statements

#4 - this will sound silly, but how do i restore the points back from the metadata..( i guess i could google it...). it is something that i would be willing to try....

Other Considerations: 

#1 - I have confirmed with the survey manager. We worked on this yesterday extensively. His survey points do not match our imagery photo exactly because it isn't projected the same as his points are.... he uses survey feet, and our image doesn't.... i was able to get my points to match an aerial image we have, but i can't get that shift to happen on my points.... THIS is so confusing!! I am sorry. I think it has something to do with the survey feet vs just Feet???

#2 - just reading this... i have to be honest, i do not know how to do all this without googling it.. i have been self teaching myself everything pertaining to this topic as i go.. i think that is why i am getting so frustrated.... (and the fact that the "i" isn't auto populating as a capital letter is starting to get to me as well... haha)

#4 - i am using the desktop 10.5 . do not know enough about Pro yet.

#7- there is a total possibility that things are getting applied numerous time... I am in this hole i got myself in.... and do not see the light!! haha

You can also email me at my work email for easier means of communication lisa.rayburg@toledo.oh.gov

i can provide data that way

thanks for your help

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LanceCole
MVP Regular Contributor

Thanks Lisa for the additional information. Just for clarification, I have a few more questions:

  1. You even have not been able to get your GPS to work with just the State VRS system to the accuracy needed, excluding a site system? 
  2. You do have an account for the State VRS, correct. 
  3. Which Trimble GPS model do you have? 
  4. I assume you are using Collector Classic not the beta of Collector for ArcGIS (Aurora) on an Android device since you are using the SPace App for your RTK?
  5. What coordinate system do you ultimately want your data to be in?
  6. What coordinate system is your feature service published to AGOL?
  7. What coordinate system is your surveyors control data?
  8. Are you using ESRI basemaps or your own in Collector? If your own, what coordinate system is the basemap? 
  9. Do you need Z (elevation) data or you only working with 2D XY data?

Once you reply to these questions, I am willing to work with you to take a big step backwards and see if we can get this working for you using small steps forward.  I am a little at a handicap as I only have access to iDevices and we are using Leica equipment. So I may have a few dumb questions.

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MiaogengZhang
Esri Regular Contributor

The datum transformation can happen at multiple places: from GPS point to webmap (defined by location profile), from webmap to feature layer, from feature layer to your own geodatabase. While you tried with location profile, pay attention to other places: basemap choice, coordinate system and datum transformation setting at data frame at ArcMap. Here is a video discussed about some consideration

Collector for ArcGIS: Working with High Accuracy Data - YouTube  

LanceCole
MVP Regular Contributor

Miaogeng Zhang‌,

Excellent video...