This is a simple ASCII format whose main purpose is to easily read coordinates of discretely sampled astrophysical surveys (e.g. such as an SDSS galaxy catalog). It should be considered when using spherical coordinates systems or if distance is measured by redshift for instance.
In this format, particles properties are encoded in an ASCII array where each row corresponds to one particle and each column to one property. Each column must have a name defined in the header (the first line of the file, starting with character #). An survey_ascii file may look like this:
# ra dec z my_field +2.115401e+02 +6.313433e-01 +2.666800e-01 1 +2.115633e+02 +7.550188e-01 +1.259900e-01 0 +2.115687e+02 +8.108763e-01 +3.646600e-01 0 +2.117158e+02 +6.393598e-01 +1.143600e-01 1 +2.116826e+02 +6.528485e-01 +2.455700e-01 1 +2.116993e+02 +6.509297e-01 +1.199000e-01 0 +2.115738e+02 +7.772653e-01 +3.240600e-01 0 +2.116198e+02 +6.950604e-01 +1.987300e-01 0 +2.116773e+02 +7.085776e-01 +2.561900e-01 1
The name of a column defines its role if it matches one of the following keywords:
| Keyword | Meaning |
| px | X coordinate of the particle |
| py | Y coordinate of the particle |
| pz | Z coordinate of the particle |
| vx | X component of the velocity |
| vy | Y component of the velocity |
| vz | Z component of the velocity |
| id | an index associated to the particle |
| ra | The right ascension of the particle |
| dec | The declination of the particle |
| z | The redshift of the particle. |
When particles coordinates are defined with ra, dec or z (redshift), DisPerSE automatically transform them into cartesian coordinates using the standard LCDM model to compute distances (Omega_m=0.27, Omega_L=0.73 ). This transformation can be inverted on the output skeletons and networks using options -toRaDecZ and -toRaDecDist of skelconv and netconv.