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FSX USGS Projection

Z

Ztimbre

Messages
75
Country
unitedstates
Hi guys,

I'm hoping I can get some advice from the gurus here who are (fingers crossed) familiar with the current UGSG "National Map" orthoimagery setup.

http://nationalmap.gov/viewer.html

In the past, my projects were small enough, and the photo resolution was low enough, that one image would cover the whole project. However, some new high-resolution imagery has raised a few questions:

1. Has the USGS gone to WGS84 projection? Or do I still need to reproject my imagery? The metadata file from my download says that it is in NED83. However, the USGS site says that the base map and viewer are in WGS84 projection. Also, there is a file called "output parameters" with the following text in my download (notice that "Coordinate System ID Native" and "Coordinate System ID WGS84" are the same):

Code: 
Raster Download Information

Number of columns:  653
Number of rows:  379
Resolution in x direction:  0.299967676999973 Meter
Resolution in y direction:  0.299967676999973 Meter

Coordinate system ID Reprojected:  26914
Top edge Reprojected:  3248649.97 Meter
Bottom edge Reprojected:  3248536.16956614 Meter
Left edge Reprojected:  326139.596 Meter
Right edge Reprojected:  326335.474893081 Meter


Coordinate system ID Native:  4326
Top edge Native:  29.3550268365562 Degree
Bottom edge Native:  29.3539731640393 Degree
Left edge Native:  -100.791017492952 Degree
Right edge Native:  -100.788982526757 Degree


Coordinate system ID WGS84:  4326
Top edge WGS84:  29.3550268365562 Degree
Bottom edge WGS84:  29.3539731640393 Degree
Left edge WGS84:  -100.791017492952 Degree
Right edge WGS84:  -100.788982526757 Degree

2. Due to the high resolution of the imagery, USGS has broken up the download into several parts. I notice that the bounding coordinates are not consistent across the downloaded parts, and not consistent with the coordinates of the original selection area made in the USGS tool. (For example, the West edge coordinates change slightly between each image).

Does this mean I will need reproject each image separately? Or could I stitch them to together in Photoshop and reproject them all together?

Sorry for the long post. I expect that you may need some more details, but I don't want to bombard the thread up front. I'm glad to provide additional info/examples if what I have written is not clear.

Thanks!
Z
 
Last edited:
Ztimbre said:
Hi guys,

I'm hoping I can get some advice from the gurus here who are (fingers crossed) familiar with the current UGSG "National Map" orthoimagery setup.

http://nationalmap.gov/viewer.html

In the past, my projects were small enough, and the photo resolution was low enough, that one image would cover the whole project. However, some new high-resolution imagery has raised a few questions:

1. Has the USGS gone to WGS84 projection? Or do I still need to reproject my imagery? The metadata file from my download says that it is in NED83. However, the USGS site says that the base map and viewer are in WGS84 projection. Also, there is a file called "output parameters" with the following text in my download (notice that "Coordinate System ID Native" and "Coordinate System ID WGS84" are the same):

Code: 
Raster Download Information

Number of columns:  653
Number of rows:  379
Resolution in x direction:  0.299967676999973 Meter
Resolution in y direction:  0.299967676999973 Meter

Coordinate system ID Reprojected:  26914
Top edge Reprojected:  3248649.97 Meter
Bottom edge Reprojected:  3248536.16956614 Meter
Left edge Reprojected:  326139.596 Meter
Right edge Reprojected:  326335.474893081 Meter


Coordinate system ID Native:  4326
Top edge Native:  29.3550268365562 Degree
Bottom edge Native:  29.3539731640393 Degree
Left edge Native:  -100.791017492952 Degree
Right edge Native:  -100.788982526757 Degree


Coordinate system ID WGS84:  4326
Top edge WGS84:  29.3550268365562 Degree
Bottom edge WGS84:  29.3539731640393 Degree
Left edge WGS84:  -100.791017492952 Degree
Right edge WGS84:  -100.788982526757 Degree

2. Due to the high resolution of the imagery, USGS has broken up the download into several parts. I notice that the bounding coordinates are not consistent across the downloaded parts, and not consistent with the coordinates of the original selection area made in the USGS tool. (For example, the West edge coordinates change slightly between each image).

Does this mean I will need reproject each image separately? Or could I stitch them to together in Photoshop and reproject them all together?

Sorry for the long post. I expect that you may need some more details, but I don't want to bombard the thread up front. I'm glad to provide additional info/examples if what I have written is not clear.

Thanks!
Z
Click to expand...

As far as i now you must reproject each File, but currently im writing a Programm that does that automatic.

About downloading in WGS84 it would be great, but i dont know about it.


Regards Benjamin
 
Hi,

As far as I know they use UTM/LCC projections for the different states. A tool like gdalinfo would tell you this.

I have found that with multiple images it is sometimes easier to first mosaic them in the projection and then reproject the combined image to WGS84. Else you could get small seams due to the reprojection.
 
Thank you guys.

Arno - I had forgotten that gdalinfo would do that. I'll take a look.

Regarding reprojection, yes, I've had that problem before when combining reprojected images. So, if you reproject the whole mosaic, what would you choose for the bounding coordinates, since they differ slightly between individual images?

Thanks!
 
Hi,

I think the images will line up perfectly in their projected coordinate system, I guess it is just the lat/lon coordinates that do not.

If you use gdal_merge to make the mosaic you don't have to choose any bounding coordinates, it just uses the geo information already in the files.
 
Thanks Arno. I had just found my way to gdal_merge about an hour ago. Testing now. I appreciate your response, and will research more carefully before asking questions.
 
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