OK, I asked this previously but solved it on my own last time. Same project, but differant shp files.

I recieved from a client shp files that were made in GPSeismic 2011. Upon recieving the shp files from client, he sent the 5 files (dbf, shp, shx, txt and sp1) as you can see in the screen shot.

The POREC did not have the prj (coordinates) so I put in the correct coordinates that are being used. I've tried the coords that we are currently using, "undefined" coords, even did the same with the surface shp file prj, switched that to 'undefined'. Nothing seems to work. The postplot keeps falling into the same place, just to the East even with differant coords.

What is going on with this, I make the coordinate changes in ArcCatalog as I have ArcView 9.3. I have two projects as this is the 2d one, the first one I had no problem with the coords as the client sent the shp files made with the GPSeismic software program. My Proj Manager could not get this to line up on her computer either.

Waht could be the problem AND SOLUTION? Could the SP1 file be the problem?

enter image description here

sp1 file below (partial)

enter image description here

  • PROBLEM SOLVED! This is what you do to fix the projection issue if your client is using GPSeismic software which at times has prj issues with ArcMap software. 1. Open ArcTool Box 2. Click DATA MANAGEMENT TOOLS 3. Click PROJECTION AND TRANSFORMATION 4. Double click DEFINE PROJECTION INPUT DATASET of FEATURE CLASS 1. Click the drop down and SELECT the POSTPLOT layter 2. Click the tiny box to the right of the COORDINATE SYSTEM 3. Select the correct proj NAD27….. NORTHERN ND …. 4. Click OK 5. GOOD TO GO, everything should line up. – Zoran Jul 19 '11 at 0:23
  • If you would, please don't use coords or coordinates when you mean coordinate system (aka coordinate reference system). I can't make out any details on the graphics. What coordinate system is the other layer using? I can see it's state plane but which one and on what GCS/datum? The GPS sp1 file includes NAD27 in its name. What coordsys is assigned to it? ArcGIS should ignore the .sp1 file; it's not a usual file, and doesn't have the same 'name' as the others. – mkennedy Jul 19 '11 at 0:24
  • roger, kennedy. I will use coordsys. It is using NAD_1983_StatePlane_North_Dakota_North_FIPS_3301_Feet... This is the first time I'm working with a Microseismic survey company doing 2D work so this was new. What exactly is .sp1 used for? thanks, Zoran – Zoran Jul 19 '11 at 0:26
  • No idea! It's not an Esri file. Is it text? What are the contents? – mkennedy Jul 19 '11 at 2:15
  • kennedy, i have the sp1 file contents at the bottom of the img's. – Zoran Jul 19 '11 at 3:42

I'm going to to go out on a limb here based on your new information. Your base data is using NAD 1983 State Plane North Dakota North zone, in US survey feet. The sp1 file for the GPS data says that it's using NAD 1927 State Plane North Dakota North zone, in meters. It's unusual to have NAD 1927 State Plane coordinates in meters. Here's what I think is happening. Between NAD 1927 and NAD 1983, the projection parameters are the same except:

NAD 1927 false easting: 2000000 US ft = 609601.2192 m

NAD 1983 false easting: 1968500.0 US ft = 600000 m

If the GPS data is really NAD 1927, but you defined it as NAD 1983 (both units matching), the one layer would be offset around 9.6km or 31500 ft east-west. There could be an additional 20-200 m offset due to the mistaken datum.

If that's what you're seeing, even though the sp1 file says meters, the data may be in feet.

Solution is to try to define the GPS data as the coordinate system that the sp1 file says. If it's really NAD 1927 ND North, in meters, you'll have to modify the existing NAD 1927 ND North definition.

  • kennedy, that makes great sense. i changed all them to NADS27. It was the microseismic surveryors software, gpseismic that was the issue. that program and arcgis at times don't talk to each other regarding projections. – Zoran Jul 19 '11 at 18:56

There are three items to look at when coordinates don't appear to match. The coordinate system, the datum the coordinates are expressed in, and the units. There are two US State Plane Coordinate systems, NAD83 and NAD27. NAD83 projection parameters are defined in meters and are referenced to the NAD83 datum while NAD27 projection parameters are defined in feet and referenced to the NAD27 datum. The header of the SP1 file shows that the coordinates are expressed in the NAD27 datum. If your coordinate system is NAD83, then the coordinates from GPSeismic have to be transformed from NAD27 to NAD83 to be match. It's that simple.

  • nice - thank you - i did not know that. – Zoran Nov 5 '11 at 23:34

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