Earthdata Forum

I am located at N36 W114. I have downloaded the complete state of Arizona for the purposes of Search and Rescue. This allows me to have terrain following data when in an area without cell or wifi service.

The problem that I am having is if I load the N36 W114 dem (dsm) file it doesn't fit the coordinates. If I load the N36 W115 dem (dsm) file, it works.

I need to have reliable data and can't spend time searching for a working file when on a search.

Can someone explain to me how this works or tell me the fix for the issue?

Hi @dnorth12 Can you please tell us which DSM you have downloaded and where you downloaded it from? There are several different DSM datasets offered from NASA. Knowing which specific one you downloaded will help us answer your questions. Thanks -- Danielle

Hi @dnorth12 I see in another email thread we have going that you mentioned ASTGTM. That is one of ours, we are looking into this. Thanks -- Danielle

This is the site that I downloaded from after signing in. https://search.earthdata.nasa.gov/search

@dnorth12 Our science team provided some guidance to your question. The coordinate in the granule/file refers to the center of the pixel at the lower left (southeast) corner of the granule. The granule N36W115 covers from 36 degrees north to 37 degrees north latitude and 114 degrees west to 115 degrees west longitude. The original file that the user downloaded would cover the same latitude but 113 W to 114 W.

From page 2 of the ASTGTM User Guide: https://lpdaac.usgs.gov/documents/434/ASTGTM_User_Guide_V3.pdf

2. Data Product Files
Each ASTER GDEM tile has two associated files: a DEM file with elevation information and a quality
assessment (QA) NUM file. Both files have a dimension of 3601 samples by 3601 lines, which
corresponds to 1 degree by 1 degree data area. The names of individual data tiles refer to the latitude
and longitude at the geometric center of the lower-left (southwest) corner pixel. For example, the
coordinates of the lower-left corner of the tile ASTGTMV003_N00E006 tile are 0 degree north
latitude and 6 degrees east longitude. ASTGTMV003_N00E006_dem and
ASTGTMV003_N00E006_num files accommodate DEM and QA data, respectively. The rows at the
north and south edges as well as the column at the east and west edges of each cell overlap and are
identical to the edge row and column in the adjacent cell.

The data coverage is north 83 degrees to south 83 degrees. The GDEM collection includes 22,912 tiles.
Please let us know if you have any further questions.
LP DAAC User Services Team

I read the explanation, but it still leaves me wondering why I had to pick the 115 file vs the 114 file when I was in the 114 coordinates. That does not make sense to me. It seems like the data isn't really where it says it is.

@dnorth12 We are waiting for further guidance from our science team.
Thank you,
Janice

hello @dnorth12 We will follow up with you via email. Thanks -- Danielle