Hello Tech.
I'm working on a project that requires National level DEM data, and I'd like to thank ESRI for providing the imagery layer (https://www.arcgis.com/home/item.html?id=0383ba18906149e3bd2a0975a0afdb8e).
Shape * | Raster exported from USGS | Raster exported from ESRI_layer | USGS_Projected | ESRI_layer_Projected | Abs(Raster exported from USGS-Raster exported from ESRI_layer) | Abs(USGS_Projected (WGS-1984)-ESRI_layer_Projected (WGS-1984)) |
Point | 3071.917 | 3071.913 | 3032.042 | 3071.913 | 0.004 | 39.871 |
Point | 3268.988 | 3268.984 | 3297.935 | 3268.984 | 0.004 | 28.951 |
Point | 3496.321 | 3496.318 | 3488.198 | 3516.118 | 0.003 | 27.92 |
Point | 2501.627 | 2501.627 | 2527.583 | 2501.627 | 0 | 25.956 |
Point | 3253.484 | 3253.491 | 3246.843 | 3271.352 | 0.007 | 24.509 |
Point | 2932.126 | 2932.129 | 2932.126 | 2955.189 | 0.003 | 23.063 |
Point | 3088.094 | 3088.087 | 3088.094 | 3110.907 | 0.007 | 22.813 |
Point | 2760.626 | 2760.628 | 2789.526 | 2766.848 | 0.002 | 22.678 |
Point | 2647.81 | 2647.816 | 2625.496 | 2647.816 | 0.006 | 22.32 |
Point | 2546.791 | 2546.793 | 2568.551 | 2546.793 | 0.002 | 21.758 |
Point | 2973.761 | 2973.768 | 2955.436 | 2976.748 | 0.007 | 21.312 |
Point | 2899.172 | 2899.171 | 2910.918 | 2889.789 | 0.001 | 21.129 |
Point | 1535.169 | 1535.16 | 1535.169 | 1514.62 | 0.009 | 20.549 |
I tried various geographical transformations and resampling methods but received no improvement. What could be the cause of this, and how should I proceed?
Looking forward to hearing from You
Solved! Go to Solution.
Hi @Jaslam,
I might have an answer for you, but I need a bit more information before I write a proper reply.
In which Projected/Geographic and Vertical Coordinate Systems is your Raster exported from USGS and Raster exported from ESRI_layer data?
I assume your target VCS for both datasets is WGS 1984, WKID::115700. Is this correct?
Thanks,
Bojan
@Jaslam,
We look at your workflow and I might be able to provide you with an explanation.
These differences are caused by a resampling technique to source the projected rasters. In your case, this would be the Nearest Neighbor method. Since your USGS_1_n45w114_20130911 and ESRI_shape have different extents and raster grids, when they are projected to WGS84 Web Mercator, their projected grids aligned differently with the source raster grids and the Nearest Neighbor method picks different pixel to source its raster value. E.g. take your point with 3071.913 height from ESRI_shape_ProjectRaster layer and check all nearest 9 pixels round that point in USGS_1_n45w114_20130911. One of the pixels will have the height of 3032.042 as it is in USGS_Proj_NAD_1983_To_WGS_1984_5 layer. Differences vary based on the elevation changes in the point’s neighborhood. Some are higher, some lower, and some are exactly equal. Similar effect, but with a bit smaller differences happens with other resampling techniques for the same reason.
Please note that the Nearest Neighbor method is inappropriate for elevation surfaces. For more details, please check Project Raster online documentation page.
I hope this helps,
Bojan
Hi @Jaslam,
I might have an answer for you, but I need a bit more information before I write a proper reply.
In which Projected/Geographic and Vertical Coordinate Systems is your Raster exported from USGS and Raster exported from ESRI_layer data?
I assume your target VCS for both datasets is WGS 1984, WKID::115700. Is this correct?
Thanks,
Bojan
Thanks @BojanŠavrič
Raster exported from ESRI layer - XY = NAD_1983 Z=None
Raster exported from USGS - XY = NAD_1983 Z=None
Target Project coordinate system is WGS 1984.
For more info sharing data set:
Attached file info:
USGS_1_n45w114_20130911 - Raster Exported from USGS
USGS_Proj_NAD_1983_To_WGS_1984_5 - Projected Raster Exported from USGS
ESRI_shape - Raster Exported from ESRI (Clipping Geometry = ID2.shp)
ESRI_shape_ProjectRaster - Projected Raster Exported from ESRI (Clipping Geometry = ID2.shp)
ID2.shp - Lower Idaho state shape file
@Jaslam,
We look at your workflow and I might be able to provide you with an explanation.
These differences are caused by a resampling technique to source the projected rasters. In your case, this would be the Nearest Neighbor method. Since your USGS_1_n45w114_20130911 and ESRI_shape have different extents and raster grids, when they are projected to WGS84 Web Mercator, their projected grids aligned differently with the source raster grids and the Nearest Neighbor method picks different pixel to source its raster value. E.g. take your point with 3071.913 height from ESRI_shape_ProjectRaster layer and check all nearest 9 pixels round that point in USGS_1_n45w114_20130911. One of the pixels will have the height of 3032.042 as it is in USGS_Proj_NAD_1983_To_WGS_1984_5 layer. Differences vary based on the elevation changes in the point’s neighborhood. Some are higher, some lower, and some are exactly equal. Similar effect, but with a bit smaller differences happens with other resampling techniques for the same reason.
Please note that the Nearest Neighbor method is inappropriate for elevation surfaces. For more details, please check Project Raster online documentation page.
I hope this helps,
Bojan