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Hello,

I have global data read in from PostGIS which I want to clip out to any one of the 5000+ coordinate reference systems (the end user might request anything) and then export to FileGDB, Shapefile or Landmark Z-Map Grid. The data is in WGS84, clipped in WSG84, and then reprojected. Some data reprojects fine (maybe based on the CRS) but others don't and I can't see why.

 

The example image below shows some data that is projected into Minna.NigeriaMid projection. In the original data, the entire earth is covered by data, but no polygons overlap. Clearly, after reprojection they do. I believe most overlaps are caused by the data being 180 degrees away from the central meridian of the Minna.NigeriaMid projection, but cannot think of a way to easily get around this. If there was a way to find the central meridian of the projection the user requests and cut the clipper 180 degrees from that, it might solve the issue?

 

I have cut my clipper area so it doesn't go beyond -179.99, -89.99 etc., and I have tried projecting to from WGS84 to LL-360 and then to Minna.NigeriaMid as suggested in this post but this didn't work. https://knowledge.safe.com/articles/34013/dateline-problem.html

 

I have tried reading in the data (WGS84) and then reprojecting both the data and the clipper to my new projection before clipping, to no avail. I'm also always getting this message when reprojecting:

"Conversion outside of usable range of Multiple Regression definition; using fallback definition."

 

I think I might also look into the option of clipping the data in the PostGIS reader.

There will also be raster data for reprojecting which I'm sure will cause more headaches!

FME is happy to reproject to whichever coordinate system you pick, but a lot will only be relevant for a small part of the globe. The Minna.NigeriaMid one is probably only good for central Nigeria (seeing as how there's a Minna.NigeriaEast and Minna.NigeriaWest too)

If you go to the Coordinate System Gallery, select a coordinate system and check out the properties you'll see the min/max lat/lons:

 

CS_NAME: Minna.NigeriaMid

 

DESC_NM: Minna / Nigeria Mid Belt

 

DT_NAME: Minna

 

EPSG: 26392

 

GROUP: AFRICA

 

MAP_SCL: 1

 

MAX_LAT: 14.45

 

MAX_LNG: 11

 

MIN_LAT: 3.283333333333333

 

MIN_LNG: 6

 

ORG_LAT: 4

 

PARM1: 8.5

 

PROJ: TM

 

QUAD: 1

 

SCL_RED: 0.99975

 

SOURCE: EPSG, V6.3, 26392 SLarge and medium scale topographic mappi]

 

UNIT: Meter

 

X_OFF: 670553.98

 

ZERO_X: 0.0001

 

ZERO_Y: 0.0001

That TM stands for Transverse Mercator, those projections are only good for a small strip a few degrees wide along it's tangent longitude.

 

 

So long story short: while FME is happy to let you reproject global data to whatever you want, in reality you'll need to limit the choices a bit.

FME is happy to reproject to whichever coordinate system you pick, but a lot will only be relevant for a small part of the globe. The Minna.NigeriaMid one is probably only good for central Nigeria (seeing as how there's a Minna.NigeriaEast and Minna.NigeriaWest too)

If you go to the Coordinate System Gallery, select a coordinate system and check out the properties you'll see the min/max lat/lons:

 

CS_NAME: Minna.NigeriaMid

 

DESC_NM: Minna / Nigeria Mid Belt

 

DT_NAME: Minna

 

EPSG: 26392

 

GROUP: AFRICA

 

MAP_SCL: 1

 

MAX_LAT: 14.45

 

MAX_LNG: 11

 

MIN_LAT: 3.283333333333333

 

MIN_LNG: 6

 

ORG_LAT: 4

 

PARM1: 8.5

 

PROJ: TM

 

QUAD: 1

 

SCL_RED: 0.99975

 

SOURCE: EPSG, V6.3, 26392 SLarge and medium scale topographic mappi]

 

UNIT: Meter

 

X_OFF: 670553.98

 

ZERO_X: 0.0001

 

ZERO_Y: 0.0001

That TM stands for Transverse Mercator, those projections are only good for a small strip a few degrees wide along it's tangent longitude.

 

 

So long story short: while FME is happy to let you reproject global data to whatever you want, in reality you'll need to limit the choices a bit.

Hi @redgeographics,

Thanks for you reply. I'm aware certain projection systems are only relvant for smaller areas but we have global clients who have access to data in various parts of the world, so we'd ideally like to give them exactly what they request, even if it doesn't serve them well! Maybe this is the wrong approach and we should introduce more parameters and validation checks for the area and the CRS they request! :)

Hi @redgeographics,

Thanks for you reply. I'm aware certain projection systems are only relvant for smaller areas but we have global clients who have access to data in various parts of the world, so we'd ideally like to give them exactly what they request, even if it doesn't serve them well! Maybe this is the wrong approach and we should introduce more parameters and validation checks for the area and the CRS they request! :)

Yes, that would be highly recommended. I understand you want to give your clients what they're asking for but if they ask for the wrong thing you may end up spending a lot of time explaining why their data looks like that.

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