# ParaView struggling with negative values (need to use logarithms)
**URL:** https://discourse.paraview.org/t/paraview-struggling-with-negative-values-need-to-use-logarithms/10211
**Category:** ParaView Support
**Tags:** vtk
**Created:** [August 29, 2022, 1:26pm UTC](https://discourse.paraview.org/t/paraview-struggling-with-negative-values-need-to-use-logarithms/10211 "2022-08-29T13:26:27Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@WarinSpace\_Game](https://discourse.paraview.org/u/WarinSpace_Game)
#### Post date: [August 29, 2022, 1:26pm UTC](https://discourse.paraview.org/t/paraview-struggling-with-negative-values-need-to-use-logarithms/10211/1 "2022-08-29T13:26:27Z")
I’ve created a little Python script to produce VTK files from my data (3D spherical → XYZ). The plot looks OK when I use linear scaling:
**VTK file:** [pattern\_linear.vtk](https://discourse.paraview.org/uploads/short-url/fdhvdWXcrzTSG0faPp1iuo6bQSP.vtk) (423.2 KB)
However, if I convert the values to dB (i.e. use `log` when exporting to VTK), a lot of values will be negative. For some reason, ParaView does not seem to like this, and gives a very different shape:
**VTK file:** [pattern\_dB.vtk](https://discourse.paraview.org/uploads/short-url/2yPyEoWtlJ9A34pbo86LlYaTxbN.vtk) (425.6 KB)
Why is that? Is there a way to help ParaView properly parse the shape I want, and not struggle with negative values? Could I change something in the VTK files?
**Edit:** using `paraview version 5.10.0-RC1`
---
### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [August 29, 2022, 1:27pm UTC](https://discourse.paraview.org/t/paraview-struggling-with-negative-values-need-to-use-logarithms/10211/2 "2022-08-29T13:27:46Z")
ParaView only display the points where you place them, you probably have an issue in your dataset generation.
---
### Author:  [@WarinSpace\_Game](https://discourse.paraview.org/u/WarinSpace_Game)
#### Post date: [August 29, 2022, 1:30pm UTC](https://discourse.paraview.org/t/paraview-struggling-with-negative-values-need-to-use-logarithms/10211/3 "2022-08-29T13:30:31Z")
@mwestphal Thanks for your input! Notice anything obvious that would fail the (r, θ, φ) → (x, y, z) conversion for negative _r_ values (`farfield`) only?
```python
def DumpFF2VTK(filename, farfield, thetaRange, phiRange, scale=1):
try:
os.remove(filename)
except OSError:
pass
t = thetaRange*math.pi/180
a = phiRange*math.pi/180
with open(filename, "w+") as fid:
fid.write("# vtk DataFile Version 3.0\n")
fid.write("Structured Grid by matlab-interface of openEMS\n")
fid.write("ASCII\n")
fid.write("DATASET STRUCTURED_GRID\n")
fid.write("DIMENSIONS 1 "+str(int(len(t)))+" "+str(int(len(a)))+"\n")
fid.write("POINTS "+str(int(len(t)*len(a)))+" double\n")
for na in range(len(phiRange)):
for nt in range(len(thetaRange)):
fid.write(str("{:e}".format(scale*farfield[nt,na]*sin(t[nt])*cos(a[na])))+" "+str("{:e}".format(scale*farfield[nt,na]*sin(t[nt])*sin(a[na])))+" "+str("{:e}".format(scale*farfield[nt,na]*cos(t[nt])))+"\n")
fid.write("\n\n")
fid.write("POINT_DATA "+str(int(len(t)*len(a)))+"\n")
fid.write("SCALARS gain double 1\nLOOKUP_TABLE default\n")
dumpField = farfield.flatten("F")
for i in dumpField:
fid.write(str("{:e}".format(i))+"\n")
```
---
### Author:  [@WarinSpace\_Game](https://discourse.paraview.org/u/WarinSpace_Game)
#### Post date: [August 29, 2022, 1:55pm UTC](https://discourse.paraview.org/t/paraview-struggling-with-negative-values-need-to-use-logarithms/10211/4 "2022-08-29T13:55:57Z")
Aha, looks like I got it. This fixed it - I basically add the absolute value of the minimum value of `r` to the `r` array conversion calculator, and now everything looks ok:
```python
for na in range(len(phiRange)):
for nt in range(len(thetaRange)):
fid.write(str("{:e}".format(
(abs(np.min(farfield))+farfield[nt,na])*sin(t[nt])*cos(a[na])))+" "+
str("{:e}".format((abs(np.min(farfield))+farfield[nt,na])*sin(t[nt])*sin(a[na])))+" "+
str("{:e}".format((abs(np.min(farfield))+farfield[nt,na])*cos(t[nt])))+"\n"
)
```
Thanks!
---
### Author:  [@WarinSpace\_Game](https://discourse.paraview.org/u/WarinSpace_Game)
#### Post date: [August 29, 2022, 2:05pm UTC](https://discourse.paraview.org/t/paraview-struggling-with-negative-values-need-to-use-logarithms/10211/5 "2022-08-29T14:05:13Z")
@mwestphal Follow-up question:
I currently write `SCALARS gain double 1` to the VTK file, and the colorbar displays that. Is it possible to include space characters in the name, like so?
```auto
SCALARS gain (dBi) double 1
```