EDM Corrections

Within GeodePy, EDM corrections can be completed. To complete an EDM correction the following data is needed.

  • Carrier wavelength of instrument

  • Modulation frequency and unit length or reference refractive index

  • Distance measured

  • Zentith angle

  • Temperature

  • Pressure

  • Relative humidity

  • (Optional) Co2 ppm

Using these we can calculate the first velocity correction and reduce to a horizontal distance.

First, the variables need to be defined. Below is the values for a Lecia Viva.

import geodepy.survey

wavelength = 0.658 #micrometers
modFreq = 9.9902213*10e6 #hz
unitLength = 1.5 #m
dist = 145.265 #m
zAngle = 91.15678 #dec
temp = 26 #°c
pressure = 1010.8 #hPa
relHum = 37 #%
co2ppm = 345 #ppm

First Velocity Parameters

Now we can calculate the first velocity parameters.

params = first_vel_params(wavelength, modFreq, None, unitLength)

print(params)

>>(286.3433 80.6752)

First Velocity Correction

Using these parameters we can calculate the first velocity correction.

correction = geodepy.survey.first_vel_corrn(dist, params, temp, pressure, relHum)

print(correction)

>>0.0020656

Now this an be applied to the distance to get a corrected distance.

corrDist = dist + correction

print(corrDist)

>>145.2670656

The first velocity correction can also be calculated using the Co2 ppm. This gives a more accurate result but requires the co2 ppm and the wavelength.

correction2 = geodepy.survey.first_vel_corrn(dist, params, temp, pressure, relHum,
                                             wavelength=wavelength, CO2_ppm=co2ppm)

print(correction2)

print(dist + correction2)

>>0.0020756
>>145.2670756

Now the horizontal distance can be found using the zenith angle and corrected distance.

horzDist = geodepy.survey.va_conv(zAngle, corrDist)

print(horzDist)

>>(-1.15678, 145.2670656, 145.2374597, -2.9326875)

Where the third value in the tuple is the horizontal distance and the last value is the change in height.