DVO provides several ways to access the photometry information stored in the database. Several simple commands allow the user to extract 1 dimensional information directly from one of the primary database tables. The commands are:

- imextract
- avextract
- mextract
- imsearch
- detsearch

### imextract

This command allows the user to extract one of the columns from the image table, applying filtering as desired:

      dvo: imextract
      USAGE: imextract (value) [-region] [-time start range] [-photcode photcode]
      dvo: imextract help
      value may be one of the following:
       ra dec airmass Mcal dMcal Xm photcode time fwhm exptime nstar ncal sky flag

The extracted data is saved in a vector with the same name used to select the column. The vector name will have the same case as the choice given, but the column selection is case-insensitive (since there are no ambiguities in the database columns names by case).

### avextract

This command allows the user to extract data from one of the Average table columns:

      dvo: avextract
      USAGE: avextract (from) (value) [options]
        from: cpt name or 'all'
        value: average.parameter or photcode
      dvo: avextract all help
      value may be one of the following:
       ra dec dmag Nmeas Nmiss Xm Xp Nphot Ncode flag type

This command takes as the first argument the name of one of the database regions. Alternatively, all regions currently displayed may be selection with the word 'all'. The second option specifies which column to select from the Average table. In addition to the basic data columns (ra, dec, etc), the magnitude-related average values (mag, dmag, Xm, Nphot, Ncode) are coupled to a photcode, which is thus required for these selections. The value 'mag' may also be subsituted with a primary or secondary photcode. Eg:

      avextract all ra : select ra for all objects in displayed region
      avextract all g  : select g magnitudes
      avextract all mag -photcode r : select r magnitudes
      avextract all Xm -photcode r  : select chisq values for r average mags

### mextract

This command allows the user to extract data from one of the Measure table columns:

      dvo: mextract
      USAGE: mextract (from) (value) [options]
        from: cpt name or 'all'
        value: measure.parameter or photcode
      dvo: mextract all help
      value may be one of the following:
       ra dR dec dD mag dmag Mrel Mcal photcode time fwhm dophot xccd yccd xmosaic ymosaic flags

This command takes as the first argument the name of one of the database regions. Alternatively, all regions currently displayed may be selection with the word 'all'. The second option specifies which column to select from the Measure table. In addition to the basic data columns (ra, dec, etc), the magnitude-related average values (mag, dmag) are coupled to a photcode, which is thus required for these selections. The value 'mag' may also be subsituted with a primary or secondary photcode. Eg:

      mextract all ra : select ra for all objects in displayed region
      mextract all g  : select g magnitudes
      mextract all mag -photcode r : select r magnitudes
      mextract all Xm -photcode r  : select chisq values for r average mags

### option filtering

The following extraction options allow the user to restrict the selections:

`-time (start) (range)`
select data for images within the given time range. The start date is given in the format YYYY/MM/DD,hh:mm:ss (any of these element may be dropped, in which case they default to 00 [for hh,mm,ss] or 01 [for MM,DD]). The date may also be written as a number of days followed by j (JD) or J (MJD). The two special date names "now" and "today" are also valid. The range is written as a number followed by a unit, with valid units of s (seconds), m (minutes), h (hours), d (days). Times are in UT. For example:``

     -time 2001/1/1 30d : select the range starting at midnight on 2001/1/1
      and ending 30 days (86400*30 seconds) later.

     -time now -3h : select the time range starting three hours ago and
      ending now.

`-region`
restrict the selection to the currently display portion of the sky. This filter expects a portion of the sky to be plotted, and will only select data for images in the part of the sky. The algorithm for selecting the displayed region may not be perfect, so images near the boundaries may be unexpected included or excluded (this depends on the exact overlap details). Multiple queries with the same region will result in the same subset of images selected. `-photcode (photcode)`
This restricts the selection to the given photcode. Images may only have photcodes of 'Dependent' type (eg, CFH12K.R.00). This filter allows the selection of images by exact match (selected photcode is Dependent type) or by equivalence match (selected photcode is Primary or Secondary type). Thus, selecting images based on CFH12K.R.00 will ignore images with photcode CFH12K.R.10, while selecting images based on photcode 'r' will return all images with CFH12K.R.*, since all are equivalent to 'r'. (NOTE: these details depend on the layout of the photcode table). fill this out with all other restrictions provided by photometry.c``