[GRASS-user] v.what.vect confusion

[Tyler Smith]

Hi again,

I'm still struggling with how to add the attribute values from a polygon map to the table for a point map. I've tried v.what.vect, as documented in my previous message. Any suggestions would be appreciated!

Thanks,

Tyler


On March 14, 2014 2:29:49 PM EDT, Tyler Smith <tyler at plantarum.ca> wrote:
>Hello,
>
>I have a vector point map, amelanchier, and a vector polygon map,
>hwSoil. I tried to extract data from hwSoil for each point in
>amelanchier as follows:
>
>v.db.addcol map=amelanchier columns="T_GRAVEL double precision"
>v.what.vect vector=amelanchier qvector=hwSoil qcolumn=T_GRAVEL \
>column=T_GRAVEL
>
>I've repeated this process for a few dozen columns.
>
>However, I'm not getting the right values. If I investigate a single
>point using d.what.vect, notice that the values for T_GRAVEL in
>amelanchier is not the same as that in hwSoil. I've included some of
>the other columns that also show small discrepancies.
>
>d.what.vect -t
>
>82:13:46.5625W(E) 36:23:46.875N(N)
>
>     hwSoil in PERMANENT  Area
>Size - Sq Meters: 10269585820.955 Hectares: 1026958.582
>           Acres: 2537669.922 Sq Miles: 3965.1093
>Layer: 1
>category: 4608
>driver: sqlite
>database: /home/tws/grassdata/hwSoilsDB/PERMANENT/sqlite.db
>table: hwsdData
>key column: MU_GLOBAL
>ADD_PROP : 0
>T_GRAVEL : 10
>T_SAND : 49
>T_SILT : 27
>T_CLAY : 24
>T_USDA_TEX_CLASS : 10
>T_REF_BULK_DENSITY : 1.4
>T_BULK_DENSITY : 1.4
>
>amelanchier in PERMANENT  Point
>Layer: 1
>category: 668
>driver: sqlite
>database: /home/tws/grassdata/hwSoilsDB/PERMANENT/sqlite.db
>table: amelanchier
>key column: cat
>cat : 668
>accession : 10-217
>species : ARB
>country : USA
>state : TN
>y : 36.3966
>x : -82.22792
>ADD_PROP : 0
>T_GRAVEL : 11
>T_SAND : 44
>T_SILT : 33
>T_CLAY : 23
>T_USDA_TEX_CLASS : 9
>T_REF_BULK_DENSITY : 1.39
>T_BULK_DENSITY : 1.35
>
>What have I done wrong here? Is v.what.vect doing some kind of
>interpolation? I've attached a small section of my map, so you can see
>that the individual points are placed within large polygons, so I
>don't think there's a chance that I'm clicking in a different polygon
>than the one the point is in.
>
>Thanks for your help!
>
>Tyler
>
>
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