Applying ground scale factor to coordinate system

[jaatagana]

I am working in a Missouri State Plane, East Zone, US Feet coordinate system. Our surveyor uses a modified state plane with a ground scale factor. They provided it to me and I tried following Alan Gilbert's video (https://www.youtube.com/watch?v=ceKHY64Xt1U&t=120s) to create a modified coordinate system. The problem is that when I do this, instead of my aerial matching my survey (aerial is georeferenced in and re-projected) it moves even further off. Instead of being a foot or two off, it's about 30' off. The aerial product I am using is Nearmap and MSDIS. Both do the same thing. The only aerials that ever lineup perfectly are the East-West Gateway aerials (https://msdis-archive.missouri.edu/archive/Missouri_Imagery/StLouisCo_Image_Consortium2018/) and they only work because they have a scale factor in their georeference that I cannot figure out how to apply to my other aerials. Any ideas? Thanks!

[Pointdump]

Hi Jervis,
Let's sort this out. Please post one of your surveyor's drawings and your NearMap or MSDIS image. (Zip 'em together)
Dave

[jaatagana]

Hi Dave,

Thank you for taking a look. Attached is an example file with some edge of pavement lines and utility concrete slabs. The slabs, in red, are the easiest to see the shift on. The MSDIS aerial is too large for me to attach, but here is a link to the zip file of the aerial from their site: https://msdis-archive.missouri.edu/archive/Missouri_Imagery/Statewide2015/ . It is the "Jefferson.zip" aerial.

[ChicagoLooper]

Hi @jaatagana 

Their are two issues you must be aware of when dealing with Near Map.

1. Your Near Map image is georeferenced. It is projected to WGS84.PseudoMercator, EPSG 3857. 

<<Warning: Different programs refer to this projection using different descriptions. Even though their projection may seem like another coordinate system altogether, they'll be the same. You can verify by examining their respective parameters.>>

Example: I've seen another program may refer to this as Mercator Google Maps (Sphere Radius 6378138).

2. The path to your Near Map image cannot exceed 128 characters. For example, beginning from C : \ to the jpg inYourImage.jpg, can't be more than 128 characters. 

You can view the Near Map instructions >>HERE<<.

[jaatagana]

Hi ChicagoLooper, thank you for taking a look. I was able to get the Nearmap aerial to come in correctly by setting the "image coordinates" to EPSG 3857 and shortening the name. It comes in correctly in state plane. I just can't figure out how to get it to adjust to the "modified" state plane coordinate with the ground scale factor.

[ChicagoLooper]

Hi @jaatagana 

As per the video you refer to in your opening post, did you create a 'duplicate' coordinate system for MO83-EF and did you modify that duplicate using the combined scale factor? Also, did you assign that duplicate CS to modelspace?

As per @Pointdump, it would help to get more info from you.

1. Can you upload your Near Map image?
2. Can you disclose the scale factor provided by the surveyor?

[jaatagana]

Correct I made a duplicate coordinate system with my ground scale factor. When I did that the aerial and survey went from only being a few feet off of each other to about 30' off. I believe I did all steps correctly. Attached is a screenshot of my settings for the duplicate system. The ground scale factor is 1.0000813762. The three items I changed in the duplicate system are highlighted in yellow. I took the original values from the original coordinate system and multiplied them by my ground scale factor. I can't attach the Nearmap but the MSDIS comes in at the exact same location. It is linked in message 3 and is named "Jefferson.zip". It is too large to attach here. The example survey file is attached there though.

[Pointdump]

Jervis,
I've watched Alan Gilbert's video, and am chewing on it. Maybe that's the right way to do it, but I've got doubts. The 0 False Northing bothers me. I'm going to experiment with a couple other ways.
That image is a monster. 7GB! How are you bringing the image into your drawing? MAPIINSERT, MAPCONNECT, Raster Tools?
I cropped it a bit in QGIS and am attaching it here in tif format. Geo-referenced to ESRI:102696 NAD83 SPCS Missouri East (Survey Feet).
Dave

[Pointdump]

Jervis,
Here's a different way. Duplicate, then edit, MO83-EF. Change it to "Transverse Mercator with Affine Post-Processor".
I had to use Raster Tools IINSERT to bring in the image. MAPIINSERT won't transform to the custom projection. You could also use MAPCONNECT.

ExampleSurvey_3 attached.
Dave

[jaatagana]

Hi Dave,

So I use Data Connect to bring the image in. The first screenshot with the red circle shows how the aerial comes in with me using the standard MO83-EF coordinate system. You can see it is shifted at the red slabs by about 2', like yours.

If I use the duplicate coordinate system according to that youtube video, I get pretty much the same result, still shifted.

 

I tried doing the version you just showed with the affine and it still comes in at the same spot with a couple foot shift.

It seems that no matter what it is either that 2' shift off or 30'

 

[Pointdump · Accepted solution]

Jervis,
Keep in mind the image might be off that much at that particular point. Or the linework might not be dead on.
The Transformation Tab is probably your best shot. You can bring in your imagery with either MAPIINSERT or MAPCONNECT.
Drawing ExampleSurvey_4 attached.
Dave

[ChicagoLooper · Accepted solution]

@jaatagana 

 As @Pointdump  has mentioned, the aerial photo can be off. The photo is not gospel.  

If you want to get it accurate, get numbers, such as numbers expressed in geographic Lat/Long or some other projection, e.g. a series of points consistent with 'edge of pavement' and individual points for telephone poles, electrical boxes, fire hydrants, etc.  You can connect dots in AutoCAD. Substituting an aerial photo for coordinates is risky especially when high precision is needed.

In your specific example, you can ignore the scale factor and use MO83-EF in your drawing.