Non GPS Surveyor Ground Control Points

This is the file I received from surveyor. usually i get long lat coordinates but the last two surveyors I worked with last week both gave me “assumed coordinate system” “local coordinate system”
and ODM says…“Unknown projection undefined, please use a proj.4 string or UTM (for example, “WGS84 UTM 11N”) to define the projection.”
is there a code similar to WGS84 that ODM recognizes as custom or local?

GCP Label, Northing, Easting, Elevation

Thank You!

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Assumed coordinate systems won’t work. You need corrdinate systems based on lat and long. They can be projected to utm or state plane. Ask your surveyors if they can provide lat long or utm or state plane go the numbers they provided. Next time specify which coordinate system you need the results in.


To rest my interest, do they provide assumed coordinates to protect their business? The devices they use definitely provide long lat so why else would they only have x,y,z on a local system?

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They don’t really don’t do it to protect their business.Sometime it’s based on a previously used coordinate system requested by the client, other times they just grab two numbers 1000n , 1000e and elev 100.00. Assumed coordinates are usually ground based, assuming the the world is a plane. Ok for a small job but not able to be located by lat long on the globe.

Sometimes they base the assumed coordinates on a projected coordinate system and scale to the local ground elevation - making the coordinate system assumed. Using this assumption, on small projects, the measurements they make are true ground measurements. What you read on the tape measure is correct.
As we know the world isnt a plane, it curves away from us. On a larger project they project the curved surface of the earth onto a plane. So what you measure on the plane and not true ground distances. In UTM if you measure 1000 units with the tape measure the the actual ground distance is 999.6 feet. This scale factor is not a problem for most drone surveys ( because they are relatively small) but placing them at the correct lat long is possible and the true benefit of projected coordinate systems.
Projected systems are are global and all based on lat and long making them usable with the GPS on your drone. You can place the observations in their correct position on the globe and in ODM.

Long and short of it - tell those surveyors exactly which coordinate system you require. Cheers


I really appreciate that thorough response. I guess the “36 x 48 at 60 scale” from the surveyor makes more sense now. Thank You!

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So my location is
WGS 84 / UTM zone 19N
I’ve entered

gcp59 6468.8269161083 6169.5944555858 400.7160000000
gcp60 6649.3778439549 6069.9905220585 386.8187770000
gcp61 7012.7096492001 5987.0245669833 326.1902350000
gcp62 7438.3027456189 5887.2333072082 319.2472050000
gcp63 7123.2461589308 5604.1440108270 323.9407800000
gcp64 6669.0504706699 5677.5043252947 338.0509200000
gcp65 6043.8848973293 5789.3628157910 369.1215520000
gcp66 5821.5967880792 5801.8687345524 361.3151190000
gcp67 5447.8520975599 6150.5426034868 390.8503830000
gcp68 5066.7947944458 6327.3894582740 393.6515330000
gcp69 5325.6831500793 7080.4927353583 413.8143700000
gcp70 5955.8574242275 6892.0829472815 432.6887800000
gcp71 5817.2726350049 6451.0668640904 414.1748350000
gcp72 6164.9844632685 6293.8433482196 428.4066710000
gcp73 6468.8266001603 6169.5940588467 400.7156640000

and that works, however, its on the opposite side of the equator.
it looks like all the point are in the correct orientation, except they are in south america and not in NY.
any thoughts?

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It happened to me as well: my coordinates in France ended up in Ethiopia! You have to switch east and north coordinates before importing them in GCP Editor. So the rtklib post-processing and usual coordinates converters output “E, N, altitude” coordinates; the gcp_file.txt generated by GCP Editor itself is also “E, N, altitude” but the input in GCP Editor (positions of the GCP) needs to be “N, E, altitudes”.
I always found it suprising but never took the time to ask here about the reason. Does somebody know about that?


Those coordinates are not UTM.
If you want the process to be geographically located where it belongs, you must request the PROJ string that defines the custom projection to use it as the header of the GCPs list.


I think I would be able to take the output and geo locate it with QGIS. Is there a way to utilize the local coordinates with ODM so that I can have a GCP calibrated output?
Here is another set of GCP’s I received.


I"m away from my computer today. I have a hunch those are NY State plane east zone coordinates. If you could try loading those in a GCP program ( i like GCP_Editor_Pro) using this proj4 string

+proj=tmerc +lat_0=38.8333333333333 +lon_0=-74.5 +k=0.9999 +x_0=150000 +y_0=0 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=us-ft +no_defs +type=crs

Take a look and see if the gcp’s are in the right position for your project. Just a hunch. Let me know how it goes. M

To address your initial question, you could just process the photos through ODM without GCP’s and try to georeference the photo to the provided coordinates in QGIS. I’ve never had much luck georeferencing a geotiff in QGIS. But i’m a few versions behind.

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In Ohio(USA), the eastings are at 5 times the size number from Northings, throughout the zone(Lambert Conformal).

The coordinates shown look like a near square zone … one would have to look and is if a point is north of(or east of), another to be certain that the data is N, E, Z and not E, N, Z, I know surveyors, that use either, and sometimes both.

Also, Surveyors, with any sensibilities would never deliver data that is truly baseless … all forms of GPS require a base, even if it’s virtual.

Also, the only real liability for a surveyor, is to locate markers of any sort and make some declaration that a found monument/marker actually represents a specified boundary-related location that must be verified(and certified), or previously verified(and certified), by himself.

So giving you precise, accurate, valid “things”, including pins, government monuments, concrete corners, control monuments or other such things, related to a valid coordinate zone, is very low, if not truly miniscule, on the liability scale … unless what that surveyor is giving you, not certifiable. BTW, with NO certification, this is actually Mumble Jumbo, and you use it at your peril.

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