Unknown coordinates from ASCII file

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11-12-2013 10:07 AM
JosselineLou
New Contributor
Hello,
I have a problem here, indeed, I used an ASCII file from LIDAR data but I want now to define a coordinate system. When I open the ASCII file, it gave me a list of numbers :

545023.50 299909.50 8.33
545024.50 299909.50 8.70
545025.50 299909.50 8.80
545026.50 299909.50 8.79
545027.50 299909.50 9.01
545028.50 299909.50 8.41
545029.50 299909.50 8.52
545030.50 299909.50 8.54
545031.50 299909.50 9.11
...

I understand that it is X, Y and Z coordinates but I don't know in which coordinate system. Does anyone have an idea ?
(It is supposed to be in the North of France, on the coast)

Thanks in advance,
Take care,

Joss
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MelitaKennedy
Esri Notable Contributor
Hi Joss,

Well, I tried both, and neither looks too hopeful. One landed offshore in the Channel (north of Le Havre) and the other in the middle of northern France. Here's how I did it. I added the points as an event layer using Add XY Data in ArcMap. When setting the coordinate system, I choose WGS 1984 UTM Zone 31N, but then modified it to have a false northing of -5000000. Then I added the data again, but switched columns for the x and y values, again using the modified false northing.

Can you narrow down the location beyond the coast of northwest France? Depending on how I look at it, I think it could be anywhere between Brest and Le Havre. 

Melita

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JoeBorgione
MVP Esteemed Contributor
Have you checked with the data provider?
That should just about do it....
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RobertBorchert
Frequent Contributor III
Looks like UTM Meters.  I tried to place them and came up with a location to the west of Marseille.

You should go back to the source where the Lidar Data came from there should be Metadata that tells you the projection/coordinate system used.

Hello,
I have a problem here, indeed, I used an ASCII file from LIDAR data but I want now to define a coordinate system. When I open the ASCII file, it gave me a list of numbers :

545023.50 299909.50 8.33
545024.50 299909.50 8.70
545025.50 299909.50 8.80
545026.50 299909.50 8.79
545027.50 299909.50 9.01
545028.50 299909.50 8.41
545029.50 299909.50 8.52
545030.50 299909.50 8.54
545031.50 299909.50 9.11
...

I understand that it is X, Y and Z coordinates but I don't know in which coordinate system. Does anyone have an idea ?
(It is supposed to be in the North of France, on the coast)

Thanks in advance,
Take care,

Joss
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MelitaKennedy
Esri Notable Contributor
Robert,

How did you manage to use UTM? Northing values in northern France should be around 5.5million. So if I swap the order of the coordinates so that they're in northing easting z order, and add 5 million to the northings, than UTM 31 North looks like it might work.

Other French systems just don't seem to fit, even if I swap the xy values.

Melita
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JosselineLou
New Contributor
Have you checked with the data provider?


Unfortunately, I'm studying right now and the teacher who gave me the data is unable to give any precisions. In fact, the data come from those who collect the them but we don't know who and how to reach them.
Three files has been given, two ASCII files (mnt and mne) and one shema.ini file that contain :
[authie_mne.asc]
Format=CSVDelimited
[authie_mnt.asc]
Format=CSVDelimited

Nothing more has been given to us so we've got a hard time to figure the coordinates system.


Robert,

How did you manage to use UTM? Northing values in northern France should be around 5.5million. So if I swap the order of the coordinates so that they're in northing easting z order, and add 5 million to the northings, than UTM 31 North looks like it might work.

Other French systems just don't seem to fit, even if I swap the xy values.

Melita


Personnaly, the point cloud appears offshore of Nigeria when I use WGS84 UTM 31N coordinate system. How can I swap order of the coordinates or add 5 millions to the northings ?
The point cloud looks like it is on the right longitude but on the wrong side of the equator...

Thanks for your answers,
Take care,

Joss
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MelitaKennedy
Esri Notable Contributor
Hi Joss,

Well, I tried both, and neither looks too hopeful. One landed offshore in the Channel (north of Le Havre) and the other in the middle of northern France. Here's how I did it. I added the points as an event layer using Add XY Data in ArcMap. When setting the coordinate system, I choose WGS 1984 UTM Zone 31N, but then modified it to have a false northing of -5000000. Then I added the data again, but switched columns for the x and y values, again using the modified false northing.

Can you narrow down the location beyond the coast of northwest France? Depending on how I look at it, I think it could be anywhere between Brest and Le Havre. 

Melita
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JosselineLou
New Contributor
Hi Joss,

Well, I tried both, and neither looks too hopeful. One landed offshore in the Channel (north of Le Havre) and the other in the middle of northern France. Here's how I did it. I added the points as an event layer using Add XY Data in ArcMap. When setting the coordinate system, I choose WGS 1984 UTM Zone 31N, but then modified it to have a false northing of -5000000. Then I added the data again, but switched columns for the x and y values, again using the modified false northing.

Can you narrow down the location beyond the coast of northwest France? Depending on how I look at it, I think it could be anywhere between Brest and Le Havre. 

Melita


Thank you for the help, I hope you didn't spend too much time on that, the spot is located at the end the Authie river. I finally managed to find the right coordinates system, indeed, it was NTF Lambert North France. It's kind of weird that they didn't gave us the coordinate system in the first place.

Thanks for the tips, it surely will get useful in future,
Take care,

Joss
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