Elevetion files don't have the right resolution

[ahcorde]

I have been checking sand_island and mcmillan_airfield worlds. There is an issue with the resolution of the elevation files. For example, sand_island is 62x52 which is wrong according with the documentation. The right resolution is 2^n + 1 x 2^n + 1, for example 129 x 129, 513 x 513, etc.

I have modified this line in the readme.md instrucctions:

gdalwarp -te $WEST $SOUTH $EAST $NORTH $SOURCE_DEM  $OUTPUT_DEM

to

gdalwarp -te $WEST $SOUTH $EAST $NORTH $SOURCE_DEM  $OUTPUT_DEM -ts 129 129

But the elevation file is still wrong.

[ahcorde]

The elevation file (3601x3601) downloaded from https://earthexplorer.usgs.gov/ looks like:

after using the command

gdalwarp -te $WEST $SOUTH $EAST $NORTH $SOURCE_DEM  $OUTPUT_DEM -ts 129 129

NOTE: You should visualize these images with qgis otherwise you will see something like:

This is the metadata generated by gdalwarp:

---- ExifTool ----
ExifTool Version Number         : 10.80
---- System ----
File Name                       : sand_island_elevation.tif
Directory                       : media
File Size                       : 34 kB
File Modification Date/Time     : 2020:04:15 15:16:35+02:00
File Access Date/Time           : 2020:04:15 15:16:39+02:00
File Inode Change Date/Time     : 2020:04:15 15:16:35+02:00
File Permissions                : rw-r--r--
---- File ----
File Type                       : TIFF
File Type Extension             : tif
MIME Type                       : image/tiff
Exif Byte Order                 : Little-endian (Intel, II)
---- IFD0 ----
Image Width                     : 129
Image Height                    : 129
Bits Per Sample                 : 16
Compression                     : Uncompressed
Photometric Interpretation      : BlackIsZero
Strip Offsets                   : 1629 9627 17625 25623 33621
Samples Per Pixel               : 1
Rows Per Strip                  : 31
Strip Byte Counts               : 7998 7998 7998 7998 1290
Planar Configuration            : Chunky
Sample Format                   : Signed
Pixel Scale                     : 8.99224806200556e-05 8.99224806201658e-05 0
Model Tie Point                 : 0 0 0 -157.89455503876 21.3179060387597 0
GDAL Metadata                   : <GDALMetadata>.  <Item name="DTED_CompilationDate">0002</Item>.  <Item name="DTED_DataEdition">02</Item>.  <Item name="DTED_DigitizingSystem">SRTM      </Item>.  <Item name="DTED_HorizontalAccuracy">0009</Item>.  <Item name="DTED_HorizontalDatum">WGS84</Item>.  <Item name="DTED_MaintenanceDate">0000</Item>.  <Item name="DTED_MaintenanceDescription">0000</Item>.  <Item name="DTED_MatchMergeDate">0000</Item>.  <Item name="DTED_MatchMergeVersion">A</Item>.  <Item name="DTED_NimaDesignator">DTED2</Item>.  <Item name="DTED_OriginLatitude">0210000N</Item>.  <Item name="DTED_OriginLongitude">1580000W</Item>.  <Item name="DTED_Producer">USCNIMA </Item>.  <Item name="DTED_RelHorizontalAccuracy">NA  </Item>.  <Item name="DTED_RelVerticalAccuracy">0010</Item>.  <Item name="DTED_SecurityCode_DSI">U</Item>.  <Item name="DTED_SecurityCode_UHL">U  </Item>.  <Item name="DTED_UniqueRef_DSI">J19 065        </Item>.  <Item name="DTED_UniqueRef_UHL">J19 065     </Item>.  <Item name="DTED_VerticalAccuracy_ACC">0008</Item>.  <Item name="DTED_VerticalAccuracy_UHL">0008</Item>.  <Item name="DTED_VerticalDatum">E96</Item>.  <Item name="UNITTYPE" sample="0" role="unittype">m</Item>.</GDALMetadata>.
GDAL No Data                    : -32767
---- GeoTiff ----
Geo Tiff Version                : 1.1.0
GT Model Type                   : Geographic
GT Raster Type                  : Pixel Is Point
Geographic Type                 : WGS 84
Geog Citation                   : WGS 84
Geog Angular Units              : Angular Degree
Geog Semi Major Axis            : 6378137
Geog Inv Flattening             : 298.257223563
---- Composite ----
Image Size                      : 129x129
Megapixels                      : 0.017

Relevant data

Bits Per Sample : 16
Sample Format : Signed

Is this format right for heighmaps?

@tfoote ote and @chapulina do you have some idea about what is going on here?